Demis MSc. thesis final

INFLUENCE OF NITROGEN AND PHOSPHORUS FERTILIZER
RATES ON SEED YIELD, QUALITY AND NUTRIENT UPTAKE OF
ONION (Allium cepa L.) AT KULUMSA IN ARSI ZONE, SOUTH
EASTERN ETHIOPIA
MSc. THESIS
DEMIS FIKRE LIMENEH
HAWASSA UNIVERSITY
COLLEGE OF AGRICULTURE
HAWASSA, ETHIOPIA
OCTOBER, 2018

INFLUENCE OF NITROGEN AND PHOSPHORUS FERTILIZER
RATES ON SEED YIELD, QUALITY AND NUTRIENT UPTAKE OF
ONION (Allium cepa L.) AT KULUMSA IN ARSI ZONE, SOUTH
EASTERN ETHIOPIA
DEMIS FIKRE LIMENEH
MAJOR ADVISOR: HUSSEIN MOHAMMED (PhD)
CO-ADVISOR: FEKADU GEBRETENSAY (PhD)
A THESIS SUBMITTED TO
THE SCHOOL OF PLANT AND HORTICULTURAL SCIENCES
COLLEGE OF AGRICULTURE
HAWASSA UNIVERSITY
IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN
PLANT AND HORTICULTURAL SCIENCES (HORTICULTURE)
HAWASSA, ETHIOPIA
OCTOBER, 2018

SCHOOL OF GRADUATE STUDIES
HAWASSA UNIVERSITY
ADVISORS’ APROVAL SHEET
(Submission Sheet – 1)
This is to certify that the thesis entitled “Influence of Nitrogen and Phosphorus fertilizer
Rates on Seed Yield, Quality and Nutrient uptake of Onion (Allium cepa L.) at Kulumsa
in Arsi Zone, South Eastern Ethiopia” submitted in partial fulfillment of the requirement
for the degree of Master’s of Science with specialization in HORTICULTURE of the
Graduate Program of the School of Plant and Horticultural Science, Collage of Agriculture,
Hawassa University, is a record of original research carried by DEMIS FIKRE LIMENEH,
under our supervision, and no part of the thesis has been submitted for any other degree or
diploma.
The assistance and help received during the course of this investigation have been duly
acknowledged. Therefore, I/we recommend that it be accepted as fulfilling the thesis
requirements.
Hussein Mohammed (PhD) ________________________ ________________
Major Advisor Signature Date
Fekadu Gebretensay (PhD) _______________________ ________________
Co-advisor Signature Date
i

DEDICATION
I dedicate this thesis to my beloved and respected family members; especially my mother
Almaz Haile, my father Fikre Limeneh and my brother and sisters, for their love, support and
partnership in the success of my life.
ii

STATEMENT OF THE AUTHOR
First, I declare that this thesis is my bonafide work and that all sources of materials used for
this thesis have been duly acknowledged. This thesis has been submitted in partial fulfillment
of the requirements for an MSc degree at the University of Hawassa and is deposited at the
university library to be made available to borrowers under rules of the library. I solemnly
declare that this thesis is not submitted to any other institution anywhere for the awards of any
academic degree, diploma, or certificate.
Brief quotations from this thesis are allowable without special permission provided that
accurate acknowledgment of source is made. Request for this manuscript in whole or in part
may be granted by the head of the major department or the dean of the School of Graduate
Studies when in his or her judgment the proposed use of the material is in the interest of
scholarship. In all other instances, however, permission must be obtained from the author.
Name: Demis Fikre Limeneh
Signature: ____________
Place: College of Agriculture, Hawassa University, Hawassa
Date of Submission: ______________________
iii

ACKNOWLEDGEMENTS
First and foremost, I offer my obeisance to the ‘Almighty God’ for his boundless blessing,
which accompanied me in all the endeavors.
I would like to express my special gratitude and heartfelt thanks to my major research advisor
Dr. Hussein Mohammed for his encouragement, constructive suggestions and moral support
from the very beginning in executing the research work and in the write-up of this thesis. I
wish to take this opportunity to extend special gratitude and indebtedness to my research coadvisor
Dr. Fekadu Gebretensay for his inspiration, thoughtful guidance and suggestions
throughout preparation of this thesis. I would like to appreciate their patience for close follow
up of this work from the very beginning to the end. Without their dedication this work would
not have been completed on time. I also extend my sincere appreciation to staff of Melkassa
and Kulumsa Agricultural Research Centers Horticulture division, Mr Zewuge Beharu, Mr.
Gizaw wogayehu, Mr. Awoke Ali, Mr. Jibicho Geleto, Mr. Desta Tsegaye, Mr.Getachew
kebede, and Miss.Tsehay Tesema for their help in preparing experimental material, planting
and recording data.
I would like to thank of Ethiopian Institute of Agricultural Research for financial support and
also Crop Research process for giving me study leave. I am also thankful to the Management
of KARC, Center manager, Finance and Administration and Crop research process staff for
their effective and efficient services required for the implementation of my thesis research.
I am extremely grateful to my mother, my girl friend, my sisters and brothers for their
understanding and help in using whatever resources they have. I never forget their care for me
that brought me to this success.
Finally, I wish my humble thanks to one and all who have directly and indirectly contributed
to the conduct of the study.
iv

ABBREVIATIONS AND ACRONYMS
AE
ANOVA
AR
CIMMTY
CSA
EIAR
ESE
FAO
KARC
MARC
MRR
NFUE
NUE
PE
RCBD
SNNP
TSP
TSS
TSW
Agronomic Efficiency
Analysis of Variance
Apparent Recovery
International Maize and Wheat Improvement Center
Central Statistical Agency
Ethiopian Institute of Agricultural Research
Ethiopian Seed Enterprise
Food and Agricultural Organization
Kulumsa Agricultural Research Center
Melkassa Agricultural Research Center
Marginal Rate of Return
Nitrogen Fertilizer Use Efficiency
Nutrient Use Efficiency
Physiological Efficiency
Randomized Complete Block Design
South Nation Nationalities and Peoples Regions
Tri- Supper Phosphates
Total Soluble Solids
Thousand Seeds Weight
v

TABLE OF CONTENTS
Content
Page
STATEMENT OF THE AUTHOR ...................................................................... iii
ACKNOWLEDGEMENTS ................................................................................... iv
ABBREVIATIONS AND ACRONYMS ............................................................... v
TABLE OF CONTENTS ....................................................................................... vi
LIST OF TABLES ................................................................................................. ix
LIST OF FIGURES ................................................................................................ x
LIST OF TABLES IN THE APPENDICES ........................................................ xi
ABSTRACT ........................................................................................................... xii
1. INTRODUCTION ............................................................................................... 1
1.1. Background and Justification ................................................................................................... 1
1.2. General objective ...................................................................................................................... 4
1.3. Specific objectives .................................................................................................................... 4
2. LITERATURE REVIEW ................................................................................... 5
2.1. Description of Onion Crop and Distribution ............................................................................ 5
2.2. Onion Production Status in the World ...................................................................................... 5
2.3. Importance and Production Status of Onion in Ethiopia .......................................................... 6
2.4. Climate and Soil Requirements of Onion ................................................................................. 6
2.5. Flower Development and Seed Formation ............................................................................... 7
2.6. Seed Production Potential of Onion ......................................................................................... 8
2.7. Factors Affecting Seed Quality and Quantity of Onion ........................................................... 8
2.8. Components of Seed Yield ....................................................................................................... 9
2.9. Nitrogen in Plant Growth and Development .......................................................................... 10
2.9.1. Nitrogen in soils and its availability to plants .............................................................. 10
2.9.2. Role of nitrogen in onion crop ..................................................................................... 11
2.9.3. Response of onion to nitrogen fertilization .................................................................. 11
2.10. Phosphorus in Plant Nutrition ............................................................................................... 12
vi

2.10.1. Phosphorus in soils and its availability to plants ........................................................ 12
2.10.2. Roles of phosphorus in plant nutrition ....................................................................... 13
2.10.3. Phosphorus requirement of onion seed production ................................................... 14
2.11. Effect of Nitrogen and Phosphorous Fertilization on Seed Yield and Quality .................... 14
2.12. Nutrient Uptake, Concentration and Use Efficiency of Onions ........................................... 17
3. MATERIALS AND METHODS ..................................................................... 19
3.1. Description of the Study Area ................................................................................................ 19
3.2. Experimental Materials and Bulb Production ........................................................................ 21
3.3. Experimental Design and Procedure ...................................................................................... 21
3.4. Soil Sampling and Analysis .................................................................................................... 22
3.5. Plant Tissue Analysis.............................................................................................................. 23
3.6. Calculation of Plant Nutrient Uptake and Use Efficiencies ................................................... 24
3.7. Data Collection and Measurement ......................................................................................... 25
3.7.1. Crop phenology and growth parameters ...................................................................... 25
3.7.2. Seed yield and yield components ................................................................................. 25
3.7.3. Seed quality parameters ............................................................................................... 26
3.8. Data Analysis .......................................................................................................................... 27
3.9. Partial Budget Analysis .......................................................................................................... 27
4. RESULTS AND DISCUSSION ....................................................................... 29
4.1. Phenology and Growth Parameters ........................................................................................ 29
4.1.1. Days to bolting ............................................................................................................. 29
4.1.2. Days to flowering ......................................................................................................... 30
4.1.3. Days to maturity ........................................................................................................... 31
4.1.4. Plant height ................................................................................................................... 33
4.1.5. Flower stalk height and diameter ................................................................................. 34
4.2. Yield and Yield Components ................................................................................................. 38
4.2.1. Number of flower stalks per plant and flowers per umbels ......................................... 38
4.2.2. Umbel diameter ............................................................................................................ 40
4.2.3. Number of umbels per plant ......................................................................................... 41
vii

4.2.4. Number and weight of seeds per umbel ....................................................................... 43
4.2.5. Seed yield per plant and per hectare ............................................................................. 46
4.3. Seed Quality Parameters ......................................................................................................... 50
4.3.1. Thousand seeds weight ................................................................................................. 50
4.4.2. Percentage of seed germination one month later after harvest ..................................... 51
4.4. Correlation Analysis of Agronomic and Yield Components .................................................. 52
4.5. Concentration of Nitrogen (N) and Phosphorus (P) in Soils after Harvest ............................ 53
4.5.1. Total nitrogen concentration in soil ............................................................................. 53
4.5.2. Available phosphorus concentration in soils ................................................................ 54
4.6. Nutrient Accumulation of N and P in Plant Tissues and Their Uptake of Onion Plants........ 56
4.6.1. Nitrogen concentration in plant tissues ........................................................................ 56
4.6.2. Phosphorus concentration in plant tissues .................................................................... 56
4.6.3. Nitrogen uptake by leaves and seeds ............................................................................ 58
4.6.4. Whole plant nitrogen uptake ........................................................................................ 60
4.6.5. Phosphorus uptake by leaves and seeds ....................................................................... 61
4.6.6. Whole plant phosphorus uptake ................................................................................... 63
4.7. Nutrient Use Efficiency (NUE) .............................................................................................. 65
4.7.1. Agronomic efficiency (AE) of nitrogen and phosphorus ............................................. 65
4.7.2. Physiological efficiency (PE) of nitrogen and phosphorus .......................................... 67
4.7.3. Apparent recovery (AR) of nitrogen and phosphorus .................................................. 68
4.8. Correlation of N and P Concentrations in Plant Tissues, Agronomic and Yield of Onion
Uptake ......................................................................................................................................... 70
4.9. Partial Budget Analysis .......................................................................................................... 72
4.9.1. Dominance analysis, net benefit curve and marginal rate of return ............................. 75
5. SUMMARY, CONCLUTION AND RECOMMENDATIONS .................... 77
6. REFERENCES .................................................................................................. 80
7. APPENDICES ................................................................................................... 91
BIOGRAPHICAL SKETCH ............................................................................... 99
viii

LIST OF TABLES
Table
Page
1. Treatment rates of nitrogen and phosphorus fertilizer rates. .............................................. 22
2. The interaction effect of N and P fertilizers on days to bolting, days to flowering, plant
height and flower stalk diameter grown at Kulumsa in 2017/2018 .................................. 37
3. The interaction effect of N and P fertilizers influenced on number of flower stalk per
plant, umbel diameter and number of umbels per plant grown at Kulumsa in
2017/2018. ......................................................................................................................... 42
4. Main effect of nitrogen and phosphorus fertilizers affected on number of flowers per
umbel and number of seeds per umbel onion seed grown at Kulumsa in 2017/2018. ...... 45
5. The interaction effect of N and P fertilizers on seed yield per umbel, seed yield plant
and seed yield per hectare grown at Kulumsa in 2017/2018. ........................................... 49
6. The interaction effect of nitrogen (N) and phosphorus (P) fertilizers on Concentration
of total nitrogen (%) and available P in the soil after harvest in 2017/2018. .................... 55
7. Phosphorus conc. in plant tissues affected by the main effect of nitrogen and
phosphorus fertilizers grown at Kulumsa in 2017/2018. .................................................. 58
8. Interaction effects of N and P fertilizers on nitrogen concentration in leaves,
seed and up take in seed grown at Kulumsa in 2017/2018. .............................................. 62
9. The main effect of nitrogen (N) and phosphorus (P) fertilization affected on plant
uptake of N and P (kg ha -1 ) at kulumsa in 2017/2018. ...................................................... 64
10. The main effect of N and P fertilizers affected on agronomic efficiency, physiological
efficiency, and apparent recovery onion seed production in 2017/2018. ......................... 70
11. Economic analysis due to the application of N and P fertilizer levels seed yield of
Nafis onion grown at Kulumsa in 2017/2018. .................................................................. 74
12. Dominance analysis and marginal rate of return of the application of N and P
fertilizer rates on onion seed production at Arsi in 2017/2018. ........................................ 76
ix

LIST OF FIGURES
Figure
page
1. Location map of the study area ............................................................................................. 20
2. Mean monthly rain fall, maximum and minimum temperature of the study area in
2017/2018. ......................................................................................................................... 20
3. Effect of nitrogen (A) and phosphorus (B) fertilizers days to maturity of onion at
kulumsa in Arsi Zone, South Eastern Ethiopia in 2017/2018. .......................................... 33
4. Main effect of nitrogen (N) fertilizer influenced on flower stalk height of onion
grown at kulumsa in Arsi Zone, South Eastern Ethiopia in 2017/2018. ........................... 35
5. The main effect of phosphorus (P) fertilizer affected 1000 seed weight of onion at
kulumsa in Arsi Zone, South Eastern Ethiopia in 2017/2018. .......................................... 51
6. Percent of seed germination affected by the main effect of nitrogen (A) and phosphorus
(B) fertilizers on onion plant at kulumsa in Arsi Zone, South Eastern Ethiopia in
2017/2018. ......................................................................................................................... 52
x

LIST OF TABLES IN THE APPENDICES
Appendix Table
Page
1. Mean square values for yield and other agronomic traits of onion as affected by main
and interaction effects of nitrogen and phosphorus fertilization in 2017/2018 ................ 91
2. Mean estimation of P and N nutrient in the soil and onion plant tissue in response to
nitrogen and phosphorus fertilization ................................................................................ 92
3. Pearson Correlation among agronomic and yield components of onion crops in
2017/2018. ......................................................................................................................... 93
4. Pearson Correlation among N and P concentrations in soils and plant tissues and
uptake parameters in 2017/2018. ...................................................................................... 94
5. Correlation coefficients (r) among selected and related characters of N and P uptake
and their concentration in the plant tissues with agronomic and yield components in
2017/2018. ......................................................................................................................... 95
6. Main effect of nitrogen and phosphorus on plant growth and seed characters of Nafis
onion Cultivar in 2017/2018 ............................................................................................. 96
7. Soil physical and chemical properties of the surface soil (0-30 cm depth) of the
experimental site before planting in 2017/2018 ................................................................ 97
8. Weather conditions in 2016, 2017 and 2018 main cropping season at Kulumsa in
2017/2018. ......................................................................................................................... 98
xi

Influence of Nitrogen and Phosphorus fertilizer Rates on Seed Yield,
Quality and Nutrient uptake of Onion (Allium cepa L.) at Kulumsa in Arsi
Zone, South Eastern Ethiopia
ABSTRACT
Demis Fikre (BSc. in Horticulture)
Advisor: Hussien Mohammed (PhD)
Co-advisor: Fekadu Gebretensay (PhD)
Onion is an important vegetable crop commercially grown both by large and small scale
farmers in Ethiopia. Its production is constrained by a number of problems including
declining soil fertility and inappropriate fertilizer application. A study was conducted to
investigate the effects of nitrogen (N) and phosphorus (P) fertilizer rates on onion seed yield,
seed quality and nutrient uptake of onion. The experiment was conducted at Kulumsa, South
Eastern Ethiopia, using four different levels of N (0, 50,100 and 150 kg N ha -1 ) and four
levels of P (0, 35, 70 and 105 kg P 2 O 5 ha -1 ) fertilizers arranged in 4 X 4 factorial
arrangements in randomized complete block design with three replications. Selected physical
and chemical properties of soil were measured before and after planting. The available P was
increased after harvest due to the application of N and P fertilizer at the rates of 100 or 150
kg N ha -1 and 70 or 105 kg P 2 O 5 ha -1 . The result of the study revealed that almost all of the
yield and yield component parameters considered were significantly affected by the
treatments. The crop phenology, growth and yield components were significantly influenced
by the rate of N and P fertilizers and their interactions. More specifically, seed yield, seed
quality, nutrients concentration and nutrient uptake were significantly (P<0.01) varied
among treatment combinations and nutrient use efficiency was decline by increasing N and P
after optimum rates. The combination of N at 100 kg N ha -1 and P at 70 kg P 2 O 5 ha -1 gave the
highest seed yield (1858.82 kg ha -1 ) with yield increment of about 57.72% over the control
onion plants. As main factors each of N and P fertilizers at rates of 100 kg N ha -1 and 105 kg
P 2 O 5 ha -1 resulted in highest germination percentage. The higher physiological efficiency of
N (53.47 kg kg -1 ) and P(580.41 kg kg -1 ) and the highest apparent recovery of N (19.62%) and
P (2.47%) was recorded from application of 50 kg N ha -1 and P at 70 kg P 2 O 5 ha -1 and the
highest agronomic efficiency of N (10.78 kg kg -1 ) and P(15.25 kg kg -1 ) were recorded from N
at rate of 50 kg N ha -1 and P at 35 kg P 2 O 5 ha -1 respectively. The uptake of N and P were
significantly and very strongly correlated (r = 0.941**) and (r = 0.947**) with seed yield per
hectare, respectively. The combination of N at 100 kg N ha -1 and P at 70 kg P 2 O 5 ha -1 was
promising combination that generated highest net benefit 488,878.5 ETB ha -1 with the highest
marginal rate of return (36638%). Therefore, a combined application of N at 100 kg N ha -1
and P at 70 kg P 2 O 5 ha -1 rates can be recommend for onion seed famers in the study area and
areas of similar agro-ecology. However, in order to give conclusive recommendations, the
study needs to be repeated at least for one more cropping season.
Key words: Onion, plant growth, seed yield, seed quality, nutrient uptake, use efficiency
xii

1. INTRODUCTION
1.1. Background and Justification
Onion (Allium cepa L.) belonging to the family Alliaceae is one of the most important
vegetable crops commercially grown in the world. It probably originated from Central Asia
between Turkmenistan and Afghanistan where some of its relatives still grow in the wild.
Onion from Central Asia, the supposed onion ancestor had probably migrated to the Near East
and areas around the Mediterranean Sea are secondary centers of development (Malik, 2000;
Grubben and Denton, 2004; Bagali et al., 2012).
Onion is currently becoming a popular vegetable crop despite to its recent introduction to the
country because of its yield potential per unit areas, the ease of propagation method both by
seed and bulb method, and the presence of high domestic and export markets (Lemma and
Shimeles, 2003; Dawit et al., 2004; Ashenafi et al., 2014; Asfaw and Eshetu, 2015). Onion is
more widely grown in Ethiopia for local consumption and for flower export. It contributes
significant nutritional values to the human diet and has medicinal properties and is primary
consumed for its unique flavors or for its ability to enhance the flavors of other foods (Lemma
and Shimeles, 2003).
In Ethiopia, at present different vegetable crops are produced in many home gardens and also
commercially in different parts of the country (Fekadu and Dandena, 2006). Among these
vegetables, onion is one of the most important cash crops. Onion production also contributes
to commercialization of the rural economy and creates many off-farm jobs (Lemma and
Shimeles, 2003; Nikus and Fikre, 2010).
Onion seeds are well known to be highly perishable and poor in keeping quality and lose
viability within a year. One of the problems of onion production in the tropics is lack of seed
which is true to type with high germination and vigor (Currah and Proctor, 1990; Griffiths et
1

al., 2002). Onion seed is usually produced in the temperate and subtropical countries. In the
countries where high temperature prevails throughout the year, only the easy-bolting types of
onion, requiring relatively low-temperature exposure, can produce seed (Singh, 2002).
During the 2017/2018 production year, the Oromia Region’s onion production coverage was
estimated about 13,669.5 ha -1 from which 1,033,485.45 tons of onion bulbs was produced
with an average yield of 7.56 tons ha -1 . Arsi Zone is one of the potential areas for vegetable
production especially onion. Different onion varieties are widely produced by the farmers in
the district. In many parts of Arsi Zone, the off season crop (under irrigation) constitutes
much of the areas under onion production (CSA, 2017).
The price of onion botanical seed remains high in the season of onion cultivation. Seed is the
basic and essential input for any crop production (Karim et al., 1999). Seed production is a
vital part in onion growing and is highly specialized business (FAO, 2013). The yield of
onion seed in our country varies from 1000 - 1300 kg ha -1 (Lemma et al., 2006), 116.32 -
118.2 kg ha -1 (Tamrat, 2006), 75.15 - 1155.75 kg ha -1 (Teshome et al., 2014) and 748.9 -
879.4 kg ha -1 (Getachew, 2014) which is very low compared to the average seed yield in
some other countries of the world, 600 - 2000 kg ha -1 (Chadha et al., 1997) and 828 - 1446 kg
ha -1 (Aminpour and Mortzavi, 2004).
Nutrients play a significant role in improving productivity and quality of vegetable crops.
Therefore, increasing the productivity of onion with a good quality is an important target for
producers. Onions are the most weak crop plants in extracting nutrients, especially the
immobile types, because of their shallow and unbranched root system; hence they require and
often respond well to addition of fertilizers. Therefore, optimum fertilizer application and
cultivation of suitable varieties with appropriate agronomic practices in specific environment
are necessary for obtaining good yield of onion (Rizk et al., 2012).
2

Nitrogen (N) and phosphorus (P) are often referred to as the primary macronutrients because
of the large quantities taken up by plants from the soil relative to other essential nutrients
(Marschner, 1995). Nitrogen comprises (1-5%) of total dry matter of plants and is a
constituent of many fundamental cell components (Bungard et al., 1999). Phosphorus is
making up about 0.2% of a plant’s dry weight and it is essential for root development. Plants
must have phosphorus for normal growth and maturity (Fairhurst et al. 1999).
According to Fairhurst et al. (1999) P deficiency is one of the largest constraints to crop
production in many tropical soils, owing to low native content and high P fixation capacity of
the soil. When the availability is limited, plant growth is usually reduced. In soils that are
moderately low in P, onion growth and yield of onion seed can be enhanced by applied P.
Quality of onion seed can be affected by mineral nutrition, irrigation schedule or rainfall
(Lemma and Shimeles, 2003). Fertilizer practices for the onion seed crop vary widely. In
Ethiopia 90-135 kg P 2 O 5 ha -1 and 81-144 kg N ha -1 urea is used for bulb production in sandy
loam soil while 92 kg N ha -1 is used for seed production (Lemma and Shimeles, 2003; Dawit
et al., 2004; Tamirat, 2006; Abdissa et al., 2011). Nationally, there is no fertilizers
recommendation for onion seed production in Ethiopia.
Reports indicated that the low yield of onion seed in the country is due to low fertility of soil,
inappropriate fertilizer use, lack of improved varieties, and poor management practices
(Lemma and Shimelis, 2003). Among these constraints, inappropriate use of mineral fertilizer
was one of the most important management factors in Arsi Zone. In the district, 150 kg urea
ha -1 and 200 kg DAP ha -1 was traditionally used, which was recommended by Melkassa
Agricultural Research Center for bulb production at national level (Lemma and Shimelis,
2003). However, these recommendations cannot be directly adopted for the soil and growing
conditions of the Arsi Zone, which are different from the conditions in the Rift Valley region.
There is no site specific recommended rate of fertilizers for onion production in Arsi Zone.
3

The majority of the farmers in the district, however, use smaller doses of N and P fertilizers.
Some of the farmers use higher doses of N fertilizer only in the form of urea and others do not
use P fertilizer at all. The optimum rates of N and P is not determined to produce high and
quality seed yield of onion. Application of appropriate rate and type of fertilizers are vital
operations for high seed yield and quality of onions.
In order to fulfill the high demand of onion seed in Arsi Zone, high quality seed has to be
produced locally in large quantity at reduced cost of production for commercial seed and bulb
producers. This not only answers the local demand for onion seed but also reduces
dependency on imported seed from abroad. Therefore, this research was conducted with the
following objectives.
1.2. General objective
To determine the optimum nitrogen and phosphorus fertilizer rates for seed yield, seed
quality and nutrient use efficiency of onion seed in Arsi area.
1.3. Specific objectives
1. To investigate the effect of N and P rates on onion seed yield and quality;
2. To investigate the interaction effect of N and P fertilizers on onion seed yield and quality;
3. To determine the effects of N and P rates on nutrient uptake and N and P use efficiencies
and;
4. To determine economical optimum rates of N and P fertilizers for onion seed production in
Arsi area.
4

2. LITERATURE REVIEW
2.1. Description of Onion Crop and Distribution
Onion belongs to the genus Allium of the family Alliaceae and is one of the oldest cultivated
vegetable, for over 4000 years (Hanelt, 1990). It is probably originated in central Asia
between Turkmenistan and Afghanistan where some of its relatives still grow as wild plants
(Zohary and Hopf, 2000). From central Asia, the supposed onion ancestor had probably
migrated to the Near East. Then it was introduced to India and South-East Asia; and into the
Mediterranean area and from there to all the Roman Empire (Grubben and Denton, 2004).
Onion is an herbaceous biennial monocot cultivated as an annual. Onion being a biennial
crop, takes two seasons for seed production. During the first season bulbs are formed while
flower stalks and seeds are developed in the second season. Onion is grown mainly for their
bulbs, although the green shoots of salad. Onions are usually grown from seed, and flowering
and seed production are important for crop production (Brewster, 2002).
2.2. Onion Production Status in the World
Onions are the second most valuable vegetables in the world, following tomato. The
production of onion crop is worldwide because of its wide benefits in our daily foods
requirements. Onion is largely produced in the developed nations and has dominated in the
international markets due to its higher quality production and longer storage life (Opara,
2003). It is estimated that around the World, over 3,642,000 ha of onions are grown annually.
On a worldwide scale, around 80 million metric tons of onions are produced per year. China
is by far the top onion producing country in the world, accounting for approximately 28% of
the world’s onion production, followed by India, USA, Iran, Egypt, Turkey, Russia, Pakistan,
Netherlands and Brazil. The world wide onion exports are estimated at around 7 million
Metric tons. The Netherlands is the world’s largest onion exporter with a total of around
5

220,000 Metric tons followed at a distance by India (FAO, 2013). In Africa, Egypt is the
leading country by producing 22.08 million tons of onion per year for domestic and
international markets that rank as the fourth of world producer (Kulkarni et al., 2014).
2.3. Importance and Production Status of Onion in Ethiopia
Onion is a high-value bulb crop that has produced by smallholder farmers and commercial
growers for both local and export markets in Ethiopia (Shimeles, 1994). Onion is considered
as one of the most important vegetable crops produced on large scale in Ethiopia. It also
occupies an economically important place among vegetables in the country. The area under
onion is increasing from time to time mainly due to its high profitability per unit area and ease
of production, and the increases in small scale irrigation areas (Nikus and Fikre, 2010). The
major production is in the Rift Valley areas. Besides bulb production, there is a great potential
for seed production in these areas. Onion production in the country is increasing from time to
time (Lemma and Shimelis, 2003). During the 2017/2018 cropping season, the total area
under onion production was estimated to be 33, 603.39 ha -1 with an average yield of about 9.8
t ha -1 and estimated a total production of greater than 3, 274, 7525.4 tons (CSA, 2017).
2.4. Climate and Soil Requirements of Onion
Onion is a cool season crop plant that has some frost tolerance, but is best adapted to a
temperature range between 13 and 24 o C. Optimum temperatures for early seedling growth are
between 23 and 27 o C; growth is slowed at temperatures above 30 o C. Acclimated plants are
able to tolerate some freezing temperature (Jilani et al., 2010). In Ethiopia onion can grow
between 500 and 2400 m.a.s.l, but the best growing altitude so far known is between 700 and
1800 m.a.s.l (Lemma and Shimelis, 2003). Onion roots are shallow and coarse and most of
the roots occur within 15- 20 cm of the surface, and seldom extends horizontally beyond 50
cm. Onion roots are short lived, being continuously produced, rarely have branch and root
6

hairs and rarely increase in diameter. Onion can be grown in all types of soils; sandy, heavy
clay, peat organic soils or volcanic soils. However, for higher yield drained friable loam soils
with a pH of 6.0-6.8 are ideal. Onion does not thrive in soils of pH below 6.0 because of trace
elements deficiencies or, occasionally, aluminum or manganese toxicity (Brewster, 1994).
2.5. Flower Development and Seed Formation
Bolting, or inflorescence production, can occur in all the vegetable Alliums and the process is
similar in all. The inflorescence develops from the shoot apical meristem under appropriate
environmental conditions. In onion there were commonly 200 to 600 flowers per umbel,
depending on cultivar, growing conditions and whether the umbel is formed from the main
growing point or an axillary shoot. Similar umbels containing large numbers of flowers are
produced by leeks and Japanese bunching onions (Brewester, 2008).
In India the time required to reach 50% flowering ranged from 82.5 to 88.25 days from
planting. The earliness in flower development had significant effect on the diameter of the
umbels. The earliest umbel had the maximum diameter of 7.2 cm as compared to the late
flowering umbel measuring 6.68 cm in diameter. This could be probably because of the fact
that early flowering umbels benefit from maximum assimilates partitioning and better dry
matter accumulation for seed set. Thousand seed weight was affected significantly by
temperature and cultivars and ranged from 2.5 to 5.1g whereas germination percentages
ranged from 76.2 to 87% (Patil et al., 1993).
The onion seed can be produced either by bulb to seed method or seed to seed method of
production systems. The bulb to seed method of production system has the advantage of
maintaining the seed quality of onion by rouging of the off-color, miss shaped, split and
rotten types whereas the seed to seed type can be used alternatively to speed up the
production practices without affecting the varietal quality (Nikus and Fikre, 2010).
7

2.6. Seed Production Potential of Onion
Seed production is one of the most important and potential area in onion production that can
bring a high economic benefit for small scale farmers. Most tropical countries near the
equator import much of their onion seeds because temperature is not cool enough to induce
optimal flowering. However, there is also possibility of producing onion seed using artificial
Vernalization (Kimani et al., 1994). In Kenya, research conducted on three local and eight
introduced onion cultivars showed that bulbs stored at 10 o C flowered earlier than those stored
at other temperatures and those stored at 21.9 o C were the latest to flower (Kimani et al.,
1994). In Ethiopia, temperature of 9-17 0 C was indicated to be favorable for flower stalk
development and seed production (Lemma, 1998).
2.7. Factors Affecting Seed Quality and Quantity of Onion
The productivity of onion seed is much lower than other African countries of Ethiopia. For
the supply of such seeds, the informal sector is playing significant role in outreaching large
number of farmers. Most of the demand for onion seed is either met by private sectors or
unorganized program and imported seeds. The formal sector, Ethiopian Seed Enterprise
(ESE) is not generally supplying onion seed. Limited amount is catered by public sector
organizations like Ethiopian Institute of Agricultural Research (EIAR) as popularization
activities (Nikus and Fikre, 2010). One of the major onion production problems is lack of
high quality seeds and improper agronomic practices used by farmers such as fertilizers
(Ahmed and Abdella 1984). The main seed supply is from unreliable sources, where after
number of market picks the late fruits or part of the crop is kept for seeds. Such seeds are
usually of low quality (viability, vigor and genetic purity). However, they are kept for the
next season and the surplus is sold to neighbor farmers (Helen et al., 2015).
8

Factors affecting seed quality before harvest may have further impact. For example they
might increase seed deterioration rate during storage. In general, longer seed storage life is
obtained if seeds are kept dry and at low temperatures. Many vegetable seeds will maintain
germination rates of at least 50% for ten or more years. However, the relative longevity of
onion seeds under cool and dry conditions is 1-2 years (Probert et al., 2000). Seed
germination and vigor are the main seed physiological quality attributes affected during seed
deterioration. Planting season can also affect onion seed production (Helen et al., 2015).
2.8. Components of Seed Yield
The most important components for onion seed production are umbel size, flower stalk
height, number of flower stalks per plant and flower stalk diameter, which are closely related
with the size of mother bulb and cultivars (Prats et al., 1996). The number of flower stalks per
plant varied from1 to 15 per plant at Melkassa and the terminal number of 50-200 flowers
produced per umbel on depending on the number of shoots axis (Lemma, 1998).
In India, seed yield per plant was positively and significantly correlated with the number of
seed stalk per plant and seed yield per umbel. Umbel diameter was the most important index
for seed yield. This character was influenced strongly by base flower stalk diameter. While
cause and effect relationship between seed weight and the evaluated components in the
inflorescence, it was found that umbel diameter was determining seed yield. This indicated
that this character could be a good index for seed yield estimation in onion. The number of
flower stalks per plant varied from 3-15 with umbel diameter differences of 5-10 cm. The
range of flower stalk height was from 76-115 cm; the highest seed yield among the cultivars
was correlated with seed stalks number per plant and umbel diameter. The variation in yield
among the cultivars was caused by the large difference in number of umbels per plant and
number of productive florets per umbel (Prats et al., 1996; Sidhu et al., 1996).
9

2.9. Nitrogen in Plant Growth and Development
2.9.1. Nitrogen in soils and its availability to plants
Nitrogen being the most often growth limiting nutrient is found to be an essential constituent
of metabolically active compounds such as amino acids, proteins, co-enzymes and some nonpertinacious
ones(Biwas and Mukherjee, 1993). Nitrogen comprises 7% of total dry matter of
plants and is a constituent of many fundamental cell components (Bungard et. al., 1999).
Nitrogen constitutes about 5 to 6% of soil organic matter by weight and it is added to the soil
both in symbiotic and non-symbiotic forms from the atmosphere. Hence, it plays a vital role
in all living tissues of the plant. No other element has such an effect on promoting vigorous
plant growth as has N. Abundant protein tends to increase the size of the leaves, and
accordingly, brings about an increase in carbohydrate synthesis (Panhwar, 2004).
-
Plant roots take up nitrogen from the soil solution principally as nitrates NO 3 and NH 4 + ions.
Although certain plants grow best when provided mainly one or the other forms, a relatively
equal mixture of the two ions gives the best results with most plants. Nitrate is the preferred
form of N for uptake by most plants, and it usually is the most abundant form that can be
taken up in well-aerated soils. The quantities of NO - 3 found in soil at any time, however,
usually represent only enough N to support uptake for a short period. Nitrate anions move
-
easily to the root with the flow of soil water and exchange at the root surface with HCO 3 or
OH - ions that, in turn, stimulate an increase in the pH of the soil solution immediately around
the root. In contrast, ammonium cations exchange at the root surface with hydrogen ions,
thereby lowering the pH of the solution around the roots (Brady and Weil, 2002). Onion also
takes up nitrates in much greater amount than ammonium (Bosch and Currah, 2002).
10

2.9.2. Role of nitrogen in onion crop
Plant tissues usually contain more N than any other nutrient normally applied as a fertilizer.
Nitrogen is an integral component of many essential plant compounds. This nitrogen is
needed to form chlorophyll, proteins and it is a major part of all amino acids and many other
molecules essential for plant growth and other critical nitrogenous plant components such as
the nucleic acids and chlorophyll (Brady and Weil, 2002). Nitrogen in the plant controls the
utilization of phosphorus and potassium and excess could delay maturity by causing too much
vegetative growth (Gustfson, 2010). Nasreen et al. (2007) who reported increasing nitrogen
levels from 0 to 120 kg ha -1 resulted in progressive increase in seed yield of onion. Nitrogen
is also essential for carbohydrate use within plants. A good supply of nitrogen stimulates root
growth and development as well as the uptake of other nutrients (Brady and Weil, 2002).
2.9.3. Response of onion to nitrogen fertilization
Onion is a heavy feeder, requiring ample supplies of nitrogen. Too much N can result in
excessive vegetative growth, delayed maturity, increased susceptibility to diseases, reduced
dry matter contents and storability and thus result in reduced yield and quality of onion seed
(Brewster, 1994; Sørensen and Grevsen, 2001). Bolting is triggered in response to exposure
of the onion plant to conditions like low temperature or limited N supply which induces
flowers to emerge before bulb are adequately grown to suppress flower initiation (Yamasaki
and Tanaka, 2005). Al-Fraihat (2009) also stated that highest percentage of bolting was
obtained from plants fertilized with the lowest level of nitrogen (100 kg N ha -1 ). Nitrogen
fertilization significantly reduced bolting in onion. The authors reported that ratio of bolting
percentage per plot decreased by about 11 and 22% in response to the fertilization of 69 and
92 kg N ha -1 , respectively as compared to the control. Nitrogen fertilization significantly
extended the number of days required for onion crop to attain its physiological maturity
(Abdissa et al., 2011).The delay in maturity of onion bulb due to application of enhanced
11

level of nitrogen. Generally, considering the status of the soil, additional nitrogen fertilizer
levels application may be necessary in order to meet the crop N requirements (Meena et al.,
2007).
2.10. Phosphorus in Plant Nutrition
2.10.1. Phosphorus in soils and its availability to plants
Phosphorus has by far the smallest quantities in solution or in readily soluble forms in mineral
soils compared with all other macronutrients found in soils, generally ranging from 0.001
mg/L in rich, heavily fertilized soils. Plant roots absorb phosphorus dissolved in the soil
solution, mainly as phosphate ions (HPO 4
-2
and H 2 PO 4 - ), but some soluble organic
phosphorus compounds are also taken up. The chemical species of phosphorus present in the
soil solution is determined by the solution pH. In strongly acid soils (pH 4.0 to 5.5), the
monovalent anion H 2 PO – 4 dominates and is slightly more available to plants than the divalent
anion HPO -2 4 which characterize alkaline solutions (Miller and Donhaue, 1995). Phosphorus
is an immobile nutrient and continued application of phosphate fertilizers tends in time to
increase the levels of this nutrient in the soil and particularly its level in the liable forms that
can release phosphorus to the soil solution (Piezynski and Logan, 1993). By holding the pH
of soils between 6 and 7, the phosphate fixation can be kept at a minimum. Due to the general
immobility of phosphorus in the soil profile, fertilizer placement is generally more critical for
P than N. Phosphate fertilizers are commonly placed in localized bands to prevent rapid
reaction with the soil (Miller and Donahue, 1995).
Most of the P present in soils is in unavailable forms and added soluble forms of P are quickly
fixed by many soils (Tisdale et al., 1995). In most soils, the amount of P in the available form
at any one time is very low, seldom exceeding about 0.01% of the total P in the soil. Thus,
available P levels must be supplemented in most soils by adding chemical fertilizers.
12

Unfortunately, much of added P is converted to the less available secondary mineral forms.
These secondary forms are released very slowly and become useful to plants only over a
period of years (Brady and Weil, 2002).
2.10.2. Roles of phosphorus in plant nutrition
Phosphorus as an important nutritional element plays sand its part in regulates many
physiological criteria in the plant which in turn affect the total yield. One fact must be put in
mind is that, the provided P to the plant or the soil depends largely on the available
reservation of this element in the soil, so the negative or the positive results may be due to
sources stored in the soil. The presence of phosphorus in the soil encourages plant growth
because phosphorus is an essential nutrient. Practically, P is a major building block of DNA
molecules (Pant and Reddy, 2003).
Phosphorus is an essential component of deoxyribonucleic acid (DNA), the seat of genetic
inheritance and of ribonucleic acid (RNA), which directs protein synthesis in both plants and
animals. Phospholipids, which play critical roles in cellular membranes, are another class of
universally important phosphorus-containing compounds. For most plant species, the total
phosphorus content of healthy leaf tissue is not high, usually comprising only 0.2 and 0.4% of
the dry matter (Brady and Weil, 2002). In addition, reported that the two forms of P in soil
are organic and inorganic. Organic P is the most stable form of P in the soil than inorganic P.
Therefore, inorganic P is readily absorbed and used by plant if it is not fixed. Organic P is
mineralized and immobilized by microbes’ activities. Mineralization is the conversion of
organic P to inorganic P, whereas, the immobilization of P involves the formation of organic
P from inorganic P (Hinsinger, 2001).
Phosphorus is essential for numerous metabolic processes. Among the significant function
and qualities of plants on which phosphorus has an important effects are enhances many
13

aspects of plant physiology, including the fundamental processes of photosynthesis,
reproduction, nitrogen fixation, flowering, fruiting (including seed production) and
maturation. Root growth, particularly development of lateral roots and fibrous rootlets is
encouraged by phosphorus. In cereal crops, good phosphorus nutrition strengthens structural
tissues such as those found in straw or stalks, thus helping to prevent lodging (falling over).
Improvement of crop quality, especially in forages and vegetables, is another benefit
attributed to this nutrient (Brady and Weil, 2002).
2.10.3. Phosphorus requirement of onion seed production
In onions, phosphorus deficiencies reduce root and leaf growth, bulb size, and yield and can
also delay maturation (Greenwood et al., 2001). In soils that are moderately low in
phosphorus, onion growth and yield can be enhanced by applied phosphorus. Results of longterm
fertilizer trials on loamy sand soils in Germany have shown a strong response of onions
to phosphorus fertilization in the range 0 to 52 kg ha -1 phosphorus (Alt et al., 1999). Ali et al.
(2008) who reported that at 45 days after planting of onion, different phosphorus levels
resulted in significantly different plant heights where the tallest plants were observed at
higher rates of applied phosphorus while the shortest plants were from the control plots.
2.11. Effect of Nitrogen and Phosphorous Fertilization on Seed Yield and Quality
Fertilizer practices for the onion seed crop vary widely. According to Hossain et al. (2017)
application of different doses of macronutrients increased number of umbels per plot, number
of seeds per umbel, weight of seeds per umbel, seed yield per plant and per hectare. The
maximum number of seeds per umbel, weight of seed, seed yield per plant and seed yield per
hectare was found from 114 N and 42 P kg ha -1 treatment and the minimum number of seeds
per umbel, weight of seed, seed yield per plant and seed yield per hectare was found from 57
N and 21 P kg ha -1 treatment respectively. According to Abas et al. (2015) the result indicated
14

that nitrogen fertilization significantly increased the length of leaves, number of leaves, length
of flowering stalk and number of flowers per umbel. The highest records for the four growth
parameters were obtained by 90 kg N fertilization.
According to Kiros et al. (2018) who reported days to bolting, days to 50% flowering, days to
maturity, flower stalk diameter, numbers of umbels per plant, umbel diameter, and number of
seeds per umbel and seed weight per umbel were significantly affected by the main effect of
NP fertilizer rates.
According to Rabinowitch and Currah (2002) experiments conducted on 26 multilevel N-
fertilizer trials in the Netherlands showed that application rates ranging from 72 to 110 kg ha -1
could be applied as two or three split dressings, but the work did not change existing
recommendation of a fixed rate of 100-120 kg N ha -1 . Adequate nitrogen fertilization is
essential for good quality and yield of onion production. Cuocolo and Barbieri (1988)
reported that good seed yield up to 1000 kg ha -1 is produced from a range of nitrogen fertilizer
levels from 0 to 150 kg ha -1 with 30 kg ha -1 increments. Nourai et al. (2003) confirmed on
their study that seed yield has been increased in response to the increase in nitrogen level in
accordance with the increase of seed yield of individual plants.
Ali et al. (1998) reported that nitrogen fertilization had significant impact on seed yield of
onion. The report claimed that there is an increase on seed yield per umbel, per plot and per
hectare. The highest yield was recorded on 150 kg ha -1 nitrogen treated bulbs while the lowest
yield was recorded on control plots. Percent seed germination increased with an increase of
nitrogen fertilization from control. The highest percentage was at 150 kg ha -1 N but farther
increase in the dose of fertilizer did not increase the percent germination.
According to Tamrat (2006) reported that phosphorus fertilization at 46 kg ha -1 P 2 O 5 showed
significant effect on umbel diameter, number of umbels per plant, number of seeds per umbel,
15

seed yield per plant, seed germination at harvest. On the other hand, nitrogen fertilization at
138 kg ha -1 showed highly significant effect on flower stalk diameter, number of umbels per
plant, number and weight of seeds per umbel and on seed yield per plant.
Phosphorous fertilization has also great impact on seed yield and quality of onion. According
to the report of Ali et al. (2008), phosphorous fertilization increased seed yield per umbel, per
plot and per hectare. Fertilizer rate of 80 kg ha -1 significantly increased the seed yield as
compared to the control. On the other hand the weight of 1000 seed of onion did not show
significant difference between fertilized and unfertilized seeds. But the percent germination
showed great improvement with an increase of phosphorous fertilization.
According to Ahmed and Abdela (2006) nitrogen application had significantly increased the
seed yield as well as quality, but phosphorous fertilization which was done in absence of
nitrogen fertilization did not show significant effect. However, they got highly significant
response when phosphorous was applied in combination with nitrogen fertilization. The
experiments conducted over two successive seasons showed that nitrogen application had
significantly increased plant height, flower stalk thickness and seed yield. But phosphorus
fertilization in the absence of nitrogen had no significant effect on seed yield. However, a
highly significant increase in seed yield was obtained when phosphorus was used in
combination with nitrogen.
According to Getachew (2014) the result showed that the highest seed yield and yield
components and seed quality attributes were obtained from 115 P 2 O 5 and 114 N kg ha -1
combination followed by 143.6 P 2 O 5 and 142.5 kg N ha -1 . . The results showed that the main
effect of NP fertilizers and plant spacing were highly significant on flower stalk diameter,
seed yield per plot and per hectare, number of seeds per umbel and significantly affected plant
16

height and seed weight per umbel. However, NP fertilizer alone was significant on days to
bolting, umbel diameter and 1000 seed weight.
Mohamedali and Nourai (1988) indicated that the application of nitrogen fertilizer
appreciably increased seed yield per plant and umbel number per plant in Sudan. This
increment in seed yield was a result of reduced flower abortion. Fertilizer trial on onion in a
semiarid tropical soil of Nigeria showed that N and P and their interaction increased number
of umbels per original bulb, seed weight per umbel and seed yield. At 50 kg P ha -1 , the
application of 50 or 100 kg N ha -1 gave significantly higher seed yield than other N and P rate
combinations tested (Nwadukwe and Chude, 1995).
Ali et al. (2007) the results showed that plant height, tillers, flowers, seeded fruit, fruit set,
and days to blooming, seed yield and germination percentage were significantly influenced by
different treatments. The yield of seed increased with increased levels of different treatment
combination. The treatment combination at a level NK (150´120 kg ha -1 ) produced the
maximum yield of seed per hectare (515.42 kg ha -1 ) followed by 100 kg N ha -1 with 120kg ha -
1 , 150kg N ha -1 with 40, 80 kg K ha -1 respectively. He concluded that nitrogen 150 kg ha -1 with
potassium 80-120 kg ha -1 produced more effective flowering stalks and showed better
performance on seed yield and quality of onion.
2.12. Nutrient Uptake, Concentration and Use Efficiency of Onions
Response of crops to fertilizer, which is a function of nutrient uptake, is highly variable
and depends on crop, type of soil, past use of the land, local weather condition as well as
the choices of the whole season. Nitrogen fertilizer application improves phosphorus uptake
from the soil (Fragria et al., 2011; Nand et al., 2011).
The nutrient requirement of the crop can be met by nutrient available in the soil and by
nutrient additions. When fertilizer prices represent a large portion of a producer’s costs, it is
17

very important to maximize fertilizer use efficiency (Warncke et al., 2004). According to
Mengel and Kirkby (1987) the nutrient content of plant tissue reflects soil availability. The
amounts of nutrients exploited in the harvest portion of the crop will depend on the yield and
the concentration of the nutrients in the time and space, variety, soil and environmental
factors (Fragria et al., 2011; Nand et al., 2011). The amount of N needed is usually based on
soil organic matter content, crop uptake and yield levels. Nitrogen uptake levels by onion
crops may vary from less than 50 kg to more than 300 kg ha -1 , depending on cultivar, climate,
plant density, fertilization and yield levels (Soujala et al., 1998).The movement of phosphorus
in soils is very low and its uptake generally depends on the concentration gradient and
diffusion in the soil near roots (Mcpharilin and Robertson, 1999). Depending on yield levels,
phosphorus uptake rates in onion are estimated to be 15-30 kg ha -1 (Salo et al., 2002).
Fertilizer use efficiency depends to large extent on soil fertility conditions. To use fertilizers
in a sustainable manner, management practices must aim at maximizing the amount of
nutrients that are taken up by the crop and minimizing the amount of nutrients that are lost
from the soil. Improving agronomic efficiency provides both direct and indirect economic
benefits: larger yield increases can be achieved for a given quantity of fertilizer applied; or
less fertilizer is required to achieve a particular yield target (Bationo et al., 2012). Halvorson
et al. (2002) reported N fertilizer use efficiency (NFUE) by onion to be about 15%. Sammis
(1997) also reported the need for high rates of N on onion to optimize yield in New Mexico,
but expressed concern about leaching of NO – 3 N from the root zone and the low NFUE (30%)
by onion. Application of the highest level of nitrogen and P fertilizers (150 kg N and 100 kg
P ) produced the highest values of yield, quality and nutrients uptake (279.3 and 262.2 mg
plant -1 ) characters of onion respectively and the lowest was recorded from control (El-Hadidi
et al., 2016).
18

3. MATERIALS AND METHODS
3.1. Description of the Study Area
The study was conducted at Kulumsa Agricultural Research Center (KARC) which is located
at 8 o 00’ to 8 o 02’N and 39 o 07’ to 39 o 10’E with an elevation of 2210 m. a. s. l. in Tiyo district,
Arsi Administrative Zone of the Oromia Regional State. The site is found 167 km South East
of Addis Ababa. The research center is located on a very gently undulating topography with a
gradient of 0 to 10% slope. It has a low relief difference with altitude ranging from 1980 to
2230 meters .The agro- climatic condition of the area is wet with 811 mm mean annual rain
fall and it is a uni- modal rainfall pattern with extended rainy season from March to
September. However, the peak season is from July to August. The mean annual maximum
and minimum temperatures are 23.1 and 9.9 0 C, respectively. The coldest month is December
where as May is the hottest (Abayneh et al., 2003).
The weather data recorded during 2017 indicated that the area received a total annual rainfall
of 838.2 mm (Appendix Table 8). The rainfall pattern is uni-modal with extended rainy
season; from February to October. However, the peak rainy season is from July to September
(Fig. 2). The average annual minimum and maximum temperatures were 11.7 and 23.9 °C,
respectively (Fig. 2 and Appendix Table 8)
Physico-Chemical Properties of the Experimental Soil before Planting
The soil analysis result showed that the experimental site had soil pH of 6.3 with 0.18 % total
nitrogen, 2.93% and 5.05% organic carbon and organic matter content, respectively. It had
5.42 ppm available phosphorus. The soil was composed of 6.25, 30 and 63.75% sand, silt and
clay, respectively, which gave clay soil texture. The mean pH value was 6.3 indicated the soil
is slightly acidic according to the rating of Benton (2003). The optimum pH for onion
production ranges between 6 and 8 (Nikus and Fikre, 2010) .The total nitrogen of the soil was
19

moderate according to the rating of Tekalign (1991), organic matter was moderate and level
of organic carbon was high as per the description of Charman and Roper (2007). According to
Olsen et al. (1954) the soil of the experimental site was medium in available phosphorus
(Appendix Table 7).
Figure 1. Location map of the study area
Figure 2. Mean monthly rain fall, maximum and minimum temperature of the study area in
2017/2018.
20

3.2. Experimental Materials and Bulb Production
Seedlings of onion cultivar Nafis were raised in the seed bed at Kulumsa Agricultural
Research Center (KARC) in March 2017. After 45 days, seedlings were transplanted to the
field at (KARC) for bulb production. Seedlings were transplanted with a recommended
spacing of 40 cm x 20 cm x 5 cm. All the recommended agronomic and crop protection
practices such as cultivation, fertilization, weeding and pesticide application were deployed.
Once the onion is matured, bulbs were harvested and true to type bulbs which are healthy,
well shaped and size were selected for the experiment. Selected bulbs were stored at 15 o C and
kept under ambient temperature for about one month and half until it broke the dormancy and
started sprouting.
3.3. Experimental Design and Procedure
The Experimental field was cleared and ploughed three times by tractors plough according to
Kulumsa Agricultural Research Center Practice and after which it was divided into three
uniform blocks each containing 16 plots for each treatment. The sprouted onion bulbs were
planted in double rows with spacing of 50, 30 and 20 cm between water furrows, rows and
plants in rows, respectively. Distances of 1 m and 1.5 m were maintained between plots and
blocks, respectively. Each plot had four rows (ridges) which consisted of 112 plants. The
middle double rows were considered for recording of agronomic data.
The experiment was conducted under irrigation condition during the off- season of October
2017 to May 2018. The treatments consisted of four levels of N (0, 50, 100, and 150 kg ha -1
from urea (46-0-0) and four levels of P 2 O 5 (0, 35, 70, and 105 kg ha -1 from TSP (0-46-0) in a
4x4 factorial combinations. The treatment combinations were arranged in randomized
complete block design (RCBD) with three replications. A plot size of 3.2 m x 2.8 m (8.96 m 2 )
was used for each experimental unit (plot). Treatments were randomly assigned to the
21

experimental plots of each replication. The full dose of P applied at planting and half dose of
N fertilizer were applied two weeks after planting and the remaining half dose of N was sidedressed
forty five days after planting.
Table 1. Treatment rates of nitrogen and phosphorus fertilizer rates.
Nitrogen Rate
Phosphorus Rate (P 2 O 5 )
0 kg N ha -1
0 Kg P 2 O 5 ha -1
50 kg N ha -1
35 Kg P 2 O 5 ha -1
100 kg N ha -1
70 Kg P 2 O 5 ha -1
150 kg N ha -1 105 kg P 2 O 5 ha -1
Other cultural practices
The plots were irrigated as per the recommendation for the area, i.e. at the interval of four
days during the first phase of active growth of the plant. Later, the irrigation gap was
increased to seven days interval. Hoeing was done manually and the field was kept free of
weeds during the growing period. For the control of disease and insect pests, insecticides such
as Profit (3 liters ha -1 ), Agrolambex, and fungicide chemicals Ridomil (3.5 kg ha -1 ) were used.
Harvesting of umbels in the net plot area was done by a sharp sickle at maturity of the umbel
per each plot. It was started on March 9, 2018 and ended on May 15, 2018. The umbels were
dried on canvas and threshed by hand. The seeds were separated from stalks and other debris
by winnowing.
3.4. Soil Sampling and Analysis
Pre-planting soil samples were collected at 0-30 cm depth by auger from 24 spots of entire
experimental field and composited to one sample. The soil samples were taken in Zigzag
22

fashion or movement. Similarly, soil samples at the same depth were collected from three
spots in each plot just after harvest. These samples were composited to in each plot. The
composited samples were dried and passed through 2.0mm sieve before laboratory analysis.
The soil samples were analyzed for parameters relevant to the study at Kulumsa Agricultural
Research Center soil laboratory. Pre planting soil samples were analyzed for soil texture, pH,
organic carbon, organic matter, total N, and available P. Soil samples collected after harvest
was analyzed for total N and available P.
The soil pH values were determined in soil water suspension 1:2.5 using glass electrode pH
meter Jackson (1967). Determination of particle size distribution (texture) was carried out
hydrometrically Day (1965). Based on the oxidation of organic carbon with acid potassium
dichromate, Organic matter content was determined using Walkely's and Black methods
respectively (Jackson, 1967). Total N was determined as mentioned by Bremner (1965).
Available P was determined according to Olsen and Sommers (1982).
3.5. Plant Tissue Analysis
At harvest, from the middle two rows, six onion plants were randomly collected and then
bulked to give one composite plant tissue sample per plot. The samples were oven dried at 65-
70 o C to constant weight. After drying, the plant tissue samples were milled and sieved in a 1
mm sieve for laboratory analysis of plant tissue P and N concentrations.
The oven-dried onion plant sample was digested by using a sulfuric acids mixture as
described by Peterburgski (1968). The total N and P was determined using the following
methods. Total nitrogen (%) was determined according to the method described by Pregle
(1945), using micro Kjeldahl. Total phosphorus (%) was determined calorimetrically using
the chlorostannus reduce molybdo phosphoric blue color method in sulphoric system as
described by Breton (1967).
23

3.6. Calculation of Plant Nutrient Uptake and Use Efficiencies
The total uptake of nitrogen and phosphorus was calculated by multiplying the seed and
leaves yield (kg ha -1 ) with the nitrogen and phosphorus concentration (%) of each treatment
as follows:
a) N uptake of seed or leaves (kg ha -1 ) = [Yield of seed or leaves (kg ha -1 ) x N
concentration of seed or leaves (%)] x10 -2
b) P uptake of seed or leaves (kg ha -1 ) = [Yield of seed or leaves (kg ha -1 ) x P
concentration of seed or leaves (%)] x10 -2
c) Total N uptake = N uptake of seed + N uptake of leaves
d) Total P uptake = P uptake of seed + P uptake of leaves
The nutrient use efficiencies were calculated according to the following formulas (Bationo et
al., 2012; Salam et al., 2014). Agronomic efficiency (AE) is expressed as the additional
amount of economic yield per unit of nutrient applied.
Agronomic efficiency (N and P) = (Yf – Yu / Na) = kg kg -1 -------------------- (eq.1)
Where Yf is yield of the fertilized plot (kg), Yu is yield of the unfertilized plot (kg), and Na is
the quantity of nutrient applied (kg).
Physiological efficiency (N and P): PE = (Yf − Yu) / (Ntf − Ntu) ------------------------ (eq.2)
Where Yf and Yu as described yield of fertilized and unfertilized and Ntf and Ntu are the
nutrient (NP) (kg) accumulation by (total leaf and seed) in the fertilized and unfertilized plot,
respectively.
Apparent recovery (N and P): = (Nf − Nu) ∗ 100% ⁄ Na --------------------------------- (eq.3)
Where Nf and Nu are the nutrient accumulation by the total biological yield (leaf and seed) in
the fertilized and unfertilized plot (kg).
24

3.7. Data Collection and Measurement
3.7.1. Crop phenology and growth parameters
Days to bolting: It was recorded as the number of days from date of planting up to when 50%
of the plants in a plot produce flower stalk.
Days to flowering: This was recorded as the number of days from date of planting up to
when 50% of the flower stalks in each plot produced flowers.
Days to maturity: It was recorded as the number of days from date of planting up to when
50% of the plants in each plot matured or ready for harvest (when 90 % of the seed colour
changed to black or the capsule turned brown and started splitting or physiologically
matured).
Plant height (cm): refers to the mean height of six randomly selected plants from the central
rows from each plot. It was measured from the soil surface to the tip of the plant after
development of umbels of the plant.
Flowers Stalk height (cm): was recorded by measuring the plant from the leaf emerged to
the tip of flower stalk under the flower head.
Flower stalk diameter (cm): The thickness of the stalk was measured for six randomly
selected plants from the central rows from each plot at flowering stage and the average was
calculated to record the parameter.
3.7.2. Seed yield and yield components
Number of flower stalks per plant: The numbers of flower stalks of the six randomly
selected plants per plot at central rows were counted and the average was calculated and
recorded as the number of flower stalks per plant.
25

Number of umbel per plant: Six plants were selected at random. The number of umbels of
the selected plants was recorded after completion of flowering in each plot. The average of
six plants was computed.
Umbel diameter (cm): refers to the mean umbel diameter of the six randomly sampled plants
in each plot. The diameter was measured using caliper two times measuring in two opposite
direction.
Number of flowers per umbel: The numbers of flowers in each umbel was counted from
randomly selected six umbels at maximum flowering stage in each plot.
Number of seeds per umbel: Six umbels were randomly taken from the six randomly
sampled plants in each plot and then dried, threshed and counted to obtain number of seeds
per umbel.
Seed weight per umbel (g): the weight of six randomly sampled umbels harvested to
determine number of seeds per umbel were weighted and adjusted to a moisture content of
8% and the average weight of the umbel was calculated by dividing the total weight to
number of the umbels.
Seed yield per plant (g): Seed yield per plant, measured from six randomly taken plants, was
converted to mean value and recorded as seed yield per plant.
Seed yield per hectare (kg ha -1 ): There were two middle rows per plot the yield was
estimated from seed yield per plot considering changing hectare basis.
3.7.3. Seed quality parameters
1000 seeds weight (g): sample of seeds from the bulk in each plot was taken and 1000 seeds
were counted in seed counter machine and weighed using a sensitive balance and then
adjusted to the moisture content of 8%.
26

Germination percentage (%): One hundred seeds were placed on Petri dishes covered with
filter paper and allowed to imbibe water with distilled water which was kept at room
temperature until 15 days. The percent of germination has three replication the total of 48
Petri dishes. A seed was considered germinated when the radicle protrusion attained
approximately 1 mm. Then percent germination was determined from counts of normal
seedlings and the total seeds placed on petri dishes. Percent of seed germination were done
one month later after harvest.
3.8. Data Analysis
The collected data were subjected to Analysis of Variance (ANOVA) using statistical analysis
Software (SAS version 9.2, 2008). The mean separation was done using (LSD) test at 5%
probability level and simple correlation was made to determine association of parameters by
using Pearson analysis.
3.9. Partial Budget Analysis
Partial budget analysis was employed for economic analysis of fertilizer application and it
was carried out for combined seed yield data. The potential response of crop towards the
added fertilizer and price of fertilizers during planting ultimately determined the economic
feasibility of fertilizer application. The economic analysis was computed using the procedure
described by (CIMMYT, 1988)
Gross average seed yield (kg ha -1 ) (AvY): is an average yield of each treatment
Adjusted yield (AjY): is the average yield adjusted downward by a 10% to reflect the
difference between the experimental yield and yield of farmers (CIMMYT, 1988).
27

AjY = AvY- (AvY-0.1)
Gross field benefit (GFB): was computed by multiplying field/farm gate price that farmers
receive for the crop when they sale it as adjusted yield.
Total cost: is the cost of Urea and TSP used for the experiment. Their prices were based on
2017 price during planting. The costs of other inputs and production practices such as labor
cost for land preparation, planting, weeding, crop protection, and harvesting were assumed to
remain the same or the difference were insignificant among treatments.
Net benefit (NB): was calculated by subtracting the total costs from gross field benefits for
each treatment. NB = GFB – total cost
Marginal rate of return (MRR %): was calculated by dividing change in net benefit by
change in cost which is the measure of increasing in return by increasing input.
28

4. RESULTS AND DISCUSSION
4.1. Phenology and Growth Parameters
4.1.1. Days to bolting
Days to bolting was significantly (P<0.01) affected by the main effects of nitrogen (N) and
phosphorus (P) fertilizers as well as the interaction of the two factors (Appendix Table 1).
The shortest days to bolting was recorded from the combination of N at rate of 0 kg ha -1 with
P at rate of 70 and 105 kg P 2 O 5 ha -1 . The combination of N at rate of 150 kg ha -1 with P at a
rate of 0 kg P 2 O 5 ha -1 delayed days to bolting as compared to other treatment combinations
except the same N (150 kg ha -1 ) combined with 70 kg P 2 O 5 ha -1 . Days to bolting was
decreased by about 13.34% in response to the fertilization of 0 kg N ha -1 along with 70 and
105 kg P 2 O 5 ha -1 as compared to the highest N rate of (150 kg ha -1 ) with the lowest P rate of 0
and 35 kg P 2 O 5 ha -1 treatment combinations. Generally, the combination of higher rate of N
with the lower rates of P fertilizers delays days to bolting, but the lower rates of N with the
higher rates of P shortened bolting time (Table 2). This might be due to the effect of increased
N fertilization as it prolongs the period of vegetative growth. The combination of the higher
rates P with the lower rates of N resulted in significant earliness of bolting may be due to the
role of phosphorus in the life cycle of the plant in enhancing many aspects of plant
physiology, including the fundamental processes of photosynthesis, reproduction, flowering
and fruiting (including seed production) and maturation (Brady and Weil, 2002). This was
also observed by Ali et al. (2007) and Sorensen and Grevsen (2010) as too much nitrogen
promoted excessive vegetative growth and delayed bolting and maturity of onion.
The present study was in line with the findings of Tamirat (2006) who reported that the lower
nitrogen and higher phosphorus fertilizers application resulted in early bolting of Bombe Red
within 41 – 47 days. Getachew (2014) reported that days to bolting of similar onion variety
29

was between 63 to 67 days. Kiros et al. (2018) who reported the same onion variety bolted
early (about 5 to 8 days earlier) when it was grown at NP fertilizer rate of 69 kg N and 92 kg
P 2 O 5 ha -1 compared to the control plots that did not receive fertilizer rates (70 days). On the
other hand, Shemelis (2000) in his study of flower and seed production potential of onions at
Melkasa, found that Adama Red was bolted in average within 24.7 days. However, in the
present study, the earliest bolting was after 50 days and the latest up to 56.67 days in average.
The differences the number of days required for bolting could be due to the relatively cool
climatic condition of the experimental site compared with Melkassa and the cultivar
difference.
4.1.2. Days to flowering
Days to flowering was significantly (P<0.01) affected by the main effect of nitrogen (N) and
phosphorus (P) fertilizers as well as the interaction of the two factors (Appendix Table 1).
The shortest days to flowering was recorded from the combination of N at rate of 0 kg ha -1
with of P at rates of 70 and 105 kg P 2 O 5 ha -1 . The days to flowering was moderately increased
when the levels of N increased to 50-100 kg ha -1 with similar rates of P 2 O 5 (70 and 105 kg
P 2 O 5 ha -1 ). Days to flowering was delayed most when the highest rate of N (150 kg ha -1 ) was
applied with all levels of P 2 O 5 (Table 2). Days to 50% flowering decreased by about 12.07%
when 70 kg P 2 O 5 ha -1 was applied without N fertilizer as compared to the highest N level (150
kg ha -1 ) applied without P 2 O 5 . The combination of higher N levels with lower rates of P
delayed days to flowering of onion. This may probably be due to the fact that these plant
nutrients lead the crop to delayed flowering by its role in physiological and metabolic
function in the plant cells. The nutrients absorbed from the soil could have diverted and sink
into vegetative parts for photosynthesis and resulted in plants will end up with a luxurious
foliage growth. The duration of flowering was expected to be affected by the growing
30

condition. Nitrogen also has physiological functions in plant which increase the plumpness
and succulence of crops thereby encourages the vegetative growth rather than reproductive
structure development (Staurt and Griffin, 1946). The current study revealed that P fertilizer
alone promoted early flowering while addition of N delayed flowering of onion. Further
increase in N resulted in a progressive increase in days to flowering.
The current result is supported by Marschner (1995) who reported similar result. Similar
results were also reported by Tamrat (2006) increased days to flowering due to increased N
fertilizer from 0 to 138 kg ha -1 on Adam Red onion variety. Ali et al. (2007) and Kiros et al.
(2018) reported that nitrogen and phosphorous fertilizers have enhanced days to flowering.
However, contradictory results were also reported indicating none significant result from the
application of N and P fertilizers (Getachew, 2014). Early flowering of onion from the
application of P fertilizer could be due to fact that phosphorus involvement in metabolic and
physiological activities i.e., an increase in the release of P from vacuoles can initiate the
respiratory burst which correlated with fruit ripening (Woodrow and Rowan, 1979).
4.1.3. Days to maturity
The main effects of nitrogen (N) and phosphorus (P) fertilizers significantly (P<0.01) affected
days to maturity of onion. However, the interaction effect of N and P fertilizers was not
significant (P>0.05) (Appendix Table 1).
All levels of N fertilizer delayed maturity of onion as compared to the control treatment (no N
fertilizer). Days to maturity was delayed most at the highest rate of N fertilizer (150 kg ha -1 )
but this was not significantly different from 100 kg N ha -1 (Fig. 3A). Days to maturity
increased by about 3.27 and 3.92% in response to the fertilization of 100 and 150 kg N ha -1 ,
respectively as compared to the control treatment. The delay in maturity in response to N
fertilizer application could be due to the fact that N fertilization increases the vegetative
31

growth of plants and an essential nutrient for plant development and reproduction (Marschner,
1995). Nitrogen is a significant component of nucleic acids such as DNA, the genetic material
that allows cells (and eventually whole plants) to grow and reproduce . This is in agreement
with the findings of Brewster (1994) and Sørensen and Grevsen (2001) who reported that too
much N can result in excessive vegetative growth and delayed maturity. This result is
consistent with the findings of Meena et al. (2007), Abdissa et al. (2011), Morsy et al. (2012)
and Guesh (2015) who reported that maturity of onion plants was delayed in response to
increasing nitrogen application. According to Kiros et al. (2018) seed maturity was
significantly delayed when grown at 100% of 69 kg N and 92 kg P 2 O 5 ha -1 fertilizer (133.3
days), a delay of 4 to 6 days compared to lower NP rates and the control treatments.
The numbers of days taken for maturity of onion were significantly reduced when 105 kg
P 2 O 5 ha -1 was applied as compared to the control treatment (Fig. 3B). However, this treatment
was not significantly different from the other treatment received 70 kg P 2 O 5 ha -1 . The
maturity of onion was delayed at the control treatment (no P fertilizer) and P at a rate of 35 kg
P 2 O 5 ha -1 . Application of P at rate of 105 kg P 2 O 5 ha -1 reduced days to maturity by 4 days as
compared to control treatment. The early maturity effect of phosphorus application may be
related to the phosphorus effect that initiated early flowering. Since phosphorous is a part of
the structure of DNA, RNA, ATP and phospholipids in membranes it plays an important role
in basic plant carbohydrate metabolism and energy transfer systems. So, it is known that,
adequate P application leads to a general increment of most metabolic processes including
cell division, cell expansion, respiration and photosynthesis. And by shortening the vegetative
growth of a crop it could play an important role to hasten physiological activities (Hinsinger,
2001).
In conformity with the present result, application of P has been reported to hasten maturity of
onion crops (Tamrat, 2006). However, contradicting reports are also available which indicate
32

non significant effect of P fertilizer on the maturity of onion (Getachew, 2014). This
contradicting result could be due to soil variability, planting season, moisture levels, and
variety to response fertilizers, light energy, biotic factors or other environmental factors
affecting the influence of P fertilizer.
Figure 3. Effect of nitrogen (A) and phosphorus (B) fertilizers days to maturity of onion at
kulumsa in Arsi Zone, South Eastern Ethiopia in 2017/2018.
4.1.4. Plant height
Analysis of variance revealed that significantly (P<0.01) differences were observed in plant
height due to the main effect of nitrogen (N), but phosphorus (P) fertilizer did not
significantly (P>0.05) affect plant height. The interaction of these two fertilizers (N and P)
significantly (P<0.05) affected plant height of onion (Appendix Table 1).
The tallest plant was found in the combination of N and P fertilizers at a rate of 100N and 70
kg P 2 O 5 ha -1 which was statistically at par with the combination of the same N with 105 kg
P 2 O 5 ha -1 . The shortest plant height was observed in non fertilized plots of both nutrients (N
and P). The combinations of N and P at 100 N and 70 kg P 2 O 5 ha -1 respectively, brought
about 21.14% increments in plant height as compared to the control treatment of no
33

fertilizers. In general, P fertilizer without N had no significant effect on the plant height of
onion. As the rate of N increased, the height of the onion plant also increased regardless of
P 2 O 5 . Our result clearly showed that N critically determined the height of the onion plant and
particularly 100 kg N ha -1 combined with 70 kg P 2 O 5 ha -1 favored plant height (Table 2). The
increased plant height at the highest level of nitrogen was probably due to the availability of
more nutrients, which helped, in maximum vegetative growth of onion plant. N contributed to
the higher rates of vegetative growth and stem elongation due to increase in N supply which
leads to might utilization of carbohydrate to form protoplasm and more cells to enhance
growth. Plants deprived of N show decreased cell division and expansion (Hewitt and Smith,
1974).
According to Gupta and Sharma (2000), Ali et al. (2007), Nasreen et al.(2007), Getachew
(2014) and Birhanu (2016), increased in nitrogen fertilization increased the height of the plant
up to certain stage at which the growth ceases or become decreased due to the toxicity of the
fertilizer. Debashis et al. (2017) observed that application of nitrogen at rate of 175 kg ha -1
resulted in significantly higher plant height (55.23cm) of onion plant.
4.1.5. Flower stalk height and diameter
Flower stalk height was significantly (P<0.05) influenced only by the main effect of nitrogen
(N), but phosphorus (P) fertilizer and their interaction was not significant (P>0.05) (Appendix
Table 1).
The highest flower stalk height was recorded for N application at a rate of 100 kg ha -1 and this
was statistically similar with N at rate of 150 kg ha -1 . The lowest flower stalk height was
obtained from the control treatments. Application of N at 100 kg ha -1 brought by about
11.58% increments in flower stalk height as compared to the control (Fig. 4). Nitrogen is so
vital because it is a major component of chlorophyll, the compound by which plants use
34

sunlight energy to produce sugars from water and carbon dioxide (i.e., photosynthesis). This
increment of height by applied N in part could be due to major factor of N contributing to the
higher rates of vegetative growth and stem elongation when nitrogen fertilizers are applied to
the plants (Marschner, 1995; Gupta and Sharma, 2000). But P fertilization did not affect
flower stalk heights.
The result was in accordance with Sidhu et al. (1996), Tamrat (2006) and Debashis et al.
(2017) who found stalk heights for other cultivar of onion in the range of 76-93 cm which was
similar to height recorded in the present study. According to Abas et al. (2015) nitrogen
fertilization significantly increased the length of flowering stalk.
Figure 4. Main effect of nitrogen (N) fertilizer influenced on flower stalk height of onion
grown at kulumsa in Arsi Zone, South Eastern Ethiopia in 2017/2018.
Flower stalk diameter was significantly (P<0.01) influenced by the main effect of nitrogen
(N), but not phosphorus (P) fertilizer. Further, N and P fertilizers interact to influence flower
stalk diameter significantly (P<0.05) (Appendix Table 1).
From all treatment combinations the highest flower stalk diameter was obtained when N and
P was applied at the rate of 100 N with 70 P 2 O 5 kg ha -1 which was statistically similar with
35

the combined effect of 150 N and 105 kg P 2 O 5 ha -1 . Whereas, the lowest was recorded from
control treatment no fertilizers. The combination of 100 N with 70 kg P 2 O 5 ha -1 brought by
about 39% increments in flower stalk diameters as compared with the control (Table 2). In
current experiment the influence of N is pronounced regardless of the rates of P fertilizer.
Nitrogen is an essential nutrient for plant growth, development and reproduction. This could
be due to the activities of N in different physiological and metabolic processes through
increase in dry matter production. Some specific growth factors that have been associated
with phosphorus are important in cell division and development of new tissue, regulate
protein synthesis, stimulated root development, increased stalk and stem strength (Brady and
Weil, 2002).
The present result was in accordance with Kiros et al. (2018) who reported flower stalk
diameter was highest (1.503 cm) when grown at 75% of 69 kg N and 92 kg P 2 O 5 ha -1
fertilizer. Plants in the control treatment recorded the least (1.233cm). Jones (1990) who
found that significant flower stalk diameter difference from N and P fertilizer received plants.
Getachew (2014) reported that highest flower stalk diameter (1.56 cm) was recorded from NP
fertilizers 115 P 2 O 5 and 114 kg N ha -1 and the lowest (1.334 cm) was from control. Similarly
Tamrat (2006) reported that flower stalk diameter was high at the rate of 138 kg N ha -1
followed by 92 kg N ha -1 . But phosphorous fertilization did not show significant difference.
This may be soil variability, cropping season, varietal difference, soil moisture and biotic
factors. Generally, N application resulted in pronounced effect on vegetative characters of
onion than the phosphorus effect in the combined application. The moderate amount of the
experimental soil may compromise the applied P fertilizer on the vegetative characters owing
to its little inherent contributions for vegetative growth. Phosphorus plays an important role in
basic plant carbohydrate metabolism and energy transfer systems. It is known that, adequate P
application leads to a general increment of most metabolic processes including cell division,
36

cell expansion, respiration and photosynthesis. Increasing the application rate of N increased
growth parameters of onion plant.
Table 2. The interaction effect of N and P fertilizers on days to bolting, days to flowering,
plant height and flower stalk diameter grown at Kulumsa in 2017/2018
N (kg ha -1 ) P 2 O 5 (kg ha -1 ) Days to
bolting
Days to 50%
flowering
Plant
height(cm)
Flower stalk
diameter(cm)
0 0 52.33 de 88.00 f 80.17 g 1.75 d
35 52.00 e 88.67 f 81.93 g 2.13 cd
70 50.00 f 85.00 gh 84.57 fg 2.09 cd
105 50.00 f 86.60 h 85.73 fg 2.11 cd
50 0 51.67 ef 90.67 ef 93.73 cde 2.16 cd
35 53.33 bcde 91.67 de 94.73 cde 2.23 cd
70 51.67 ef 91.00 e 94.97 bcde 2.09 cd
105 52.33 de 90.33 ef 90.83 ef 2.17 cd
100 0 54.00 bcd 93.33 bcd 95.50 bcde 2.33 bc
35 53.00 e 92.33 cde 92.60 de 2.41 bc
70 52.00 cde 91.67 de 101.73 a 2.87 a
105 54.00 bcd 93.67 bcd 99.73 abc 2.42 bc
150 0 56.67 a 96.67 a 95.50 bcde 2.27 bc
35 55.00 ab 94.67 ab 95.26 bcde 2.36 bc
70 52.67 de 94.67 ab 95.33 cde 2.51 bc
105 54.67 bc 94.33 bc 97.13 abc 2.77 ab
LSD(0.05) 1.84 2.15 6.16 0.49
CV (%) 1.98 1.35 3.99 12.16
LSD 0.05 = least significant difference at 5%, CV (%) = Coefficient of variation. Means in the
same column followed by the same letter(s) are not significantly different.
37

4.2. Yield and Yield Components
4.2.1. Number of flower stalks per plant and flowers per umbels
The analysis of variance revealed that significant (P<0.01) differences were observed among
treatments in the main effects of nitrogen (N) and phosphorus (P) as well as the interaction
(P<0.05) effect of the two factors on number of flower stalks per plant (Appendix Table 1)
Numerically the highest number of flower stalk per plant was obtained from the combination
of N at a rate of 150 kg ha -1 with P at 105 kg P 2 O 5 ha -1 . This combination was statistically
similar when 100 kg N ha -1 combined with all none zero P 2 O 5 rates as well as when 150 kg N
ha -1 combined with 70 kg P 2 O 5 ha -1 (Table 3). The lowest number of flower stalk per plant
was recorded from the control treatments. Application of 150 kg N ha -1 with 105 kg P 2 O 5 ha -1
brought about 58.87% increments in number of flower stalk per plant over control treatments.
From the results, application of both N and P increased number of flower stalks per plant than
N and P alone. Generally, as the combination of both N and P 2 O 5 rates increased the number
of flower stalk per plant also increased (Table 3).
The present result is in line with that of Rashid and Singh (2000), Tamrat (2006) and
Debashis et al. (2017) who reported that increase in nitrogen fertilization increases number of
umbels and flower stalks per plant. The application rates of NP fertilizer from 0 to 50% of 69
kg N and 92 kg P 2 O 5 ha -1 fertilizer increased number of flower stalk per plant by 17.66%
(Kiros et al., 2018). However, our result contradicted with the report of Ahmed and Abdalla
(2006) and Getachew (2014) who reported that nitrogen and phosphorus separately or in
combination proved to have no effect on the number of branches or flower stalks produced
per plant. This may be due to environmental factors, soil variability, planting season, varietal
difference and past use of the land.
38

The number of flowers per umbel was significantly (P<0.01) influenced by the main effects
of nitrogen (N) and phosphorus (P) application, but their interactions were not significant
(P>0.05) (Appendix Table 1).
Numerically the highest number of flowers per umbel was obtained when N was applied at
the rate of 100 kg ha -1 which was statistically at par with N at rate of 150 kg ha -1 . The lowest
number of flowers per umbel was recorded in the control treatments (Table 4). Other report
on onion indicated that application of N has been found to increase the number of umbels per
plant and number of florets per umbel (Ahmed and Abdalla, 1984). The highest number of
flowers (198.31) was obtained from 150 kg N ha -1 applied and the lowest (138.79) form
control (Ali et al., 2007). According to Abas et al. (2015) nitrogen fertilization significantly
increased number of flowers per umbel.
Similarly the number of flowers per umbel was affected by P fertilizer. The highest number of
flowers per umbel was obtained when P was applied at the rate of 105 kg P 2 O 5 ha -1 which was
statistically at par with 70 kg P 2 O 5 ha -1 . The lowest number of flowers per umbel was
recorded from the control treatments. From the result the number of flowers per umbel
increased at higher rates of both N and P fertilizers (Table 4). This very important character
increased by P application probably due to the fact that this element was vital for flowering,
seed formation and related reproductive activities (Brady and Weil, 2002). This result is in
concordant with the findings of Muhammad et al. (1999) who reported that the highest
(618.0) number of flowers per umbel was recorded by the application of N at rate of 75 kg ha -
1
and P 46 P 2 O 5 kg ha -1 and the lowest (523.80) was recorded from control plots. The number
of flower stalks per plant varied from1 to 15 per plant at Melkassa and the terminal number of
50-200 flowers produced per umbel on “Adama Red” depending on the number of shoots axis
(Lemma, 1998). In onion there were commonly 200 to 600 flowers per umbel (Brewester,
2008).
39

4.2.2. Umbel diameter
Nitrogen (N) and phosphorus (P) fertilizers as well as their interaction significantly (P<0.01)
affected on umbel diameter of onion plant (Appendix Table 1).
Numerically the largest umbel diameter was recorded from N at a rate of 150 kg ha -1 with P at
70 kg P 2 O 5 ha -1 which was statistically similar with the combination of 100 kg N ha -1 with the
same rate of P 2 O 5 as well as when 150 kg N ha -1 combined with 105 kg P 2 O 5 ha -1 . The
combinations of both fertilizers (N and P) at the higher rates in the current experiment
resulted in larger umbel diameters. The lowest umbel diameter was recorded from control
treatments (Table 3). Application of 150 N with 70 kg P 2 O 5 ha -1 brought about 33.74%
increments in umbel diameter over control treatments. The combination of N rates with the
increasing of P showed increasing trend on umbel diameter. This might be due to that flower
setting and seed formation are highly controlled by phosphorous and the application of
nitrogen increased the vegetative growth, produced good quality foliage and promotes
carbohydrate synthesis thereby produces larger umbel diameters (Brady and Weil, 2002). The
earliness of flowering has impact on umbel size (Patil et.al., 1996). The significant increasing
of umbel diameter recorded in the study might be P nutrient might encouraged and stimulate
flower setting and might producing of wider umbel size for more flowers, then seed formation
and related reproductive activities (Brady and Weil, 2002). Since Phosphorous is a part of the
structure of DNA, RNA, ATP and phospholipids in membranes it plays an important role in
basic plant carbohydrate metabolism and energy transfer systems.
These results were in accordance with the work done by Getachew (2014) regarding the NP
fertilizers rates, the largest umbel diameter (6.267 cm) was obtained with the NP application
rates of 115 P 2 O 5 and 114 kg N ha -1 . The highest umbel diameter (5.69 cm) was obtained with
plots that received NP fertilizer at the rate of 75% of 69 kg N and 92 kg P 2 O 5 ha -1 , which was
40

significantly higher over the control (5.04 cm) (Kiros et al., 2018). Rashid and Singh (2000)
and Tamrat (2006) reported that phosphorous but not nitrogen fertilization showed significant
effect on umbel diameter.
4.2.3. Number of umbels per plant
The analysis of variance revealed that N (P<0.01) and P (P<0.01) fertilizer as well as their
interaction (P<0.05) significantly affected number of umbels per plant (Appendix Table 1).
Numerically the treatment combinations of N and P at the rate of 100 kg N ha -1 with 70 kg
P 2 O 5 ha -1 revealed the highest number of umbel per plant. The combinations of higher rates of
N (100 and 150 kg ha -1 ) with P (70 and 105 kg P 2 O 5 ha -1 ) resulted in increased number of
umbels per plant (Table 3). The lowest number of umbel per plant was recorded from control
treatments. Application of 100 kg N ha -1 with 70 kg P 2 O 5 ha -1 brought about 58.42%
increments in number of umbel per plant as compared to control treatments. This could
probably be attributed to better absorption of the nutrients by their complementary function in
stimulating of lateral root production (Drew, 1995; Thaler and pages, 1998; Zhang et al.,
1999). Number of umbel was the most important trait for onion seed yield (Prats et al., 1996).
The number of flowers stalks produced by a single plant usually varies, depending on the
number of branches formed on the shoot axis during vegetative growth (Kadams and Amans,
1991).
Similar observations were made by Rashid and Singh (2000), Tamrat (2006) and Debashis et
al. (2017) reported that increase in nitrogen fertilization increases number of umbels per
plant. Also the result of the present study supports the finding of Mohamedali and Nourai
(1988) and Nwadukwe and Chude (1995) who observed the main and interaction effects of
applied N and P increased the number of umbels per plant at the rate of 50-100 kg N ha -1 and
50 kg P 2 O 5 ha -1 . The application of NP fertilizer at 50, 75 and 100% of 69 kg N and 92 kg
41

P 2 O 5 ha -1 had significantly higher number of umbels per plant compared with the no NP
application (Kiros et al., 2018). However, our result contradicted with the report of Getachew
(2014) effect of NP fertilizers was not significant on number of flower stalks and umbels per
plant. This is may be soil moisture content, soil type, cultivar, cropping season, environmental
and biotic factors.
Table 3. The interaction effect of N and P fertilizers influenced on number of flower stalk per
plant, umbel diameter and number of umbels per plant grown at Kulumsa in 2017/2018.
N (kg ha -1 ) P 2 O 5 (kg ha -1 ) Flower stalk (palnt -
1 )
Umbel
diameter(cm)
Number of umbels
(plant -1 )
0 0 5.70 h 4.32 f 6.07 i
35 7.53 gh 4.64 ef 7.30 hi
70 10.57 cdef 5.11 cde 7.4 hi
105 10.78 cdef 5.14 cde 8.30 efgh
50 0 8.33 fg 5.24 cde 8.03 gh
35 8.95 efg 4.93 def 8.16 fgh
70 9.98 efg 5.68 bc 9.33 defg
105 10.00 cdef 5.53 cd 9.73 cdef
100 0 11.23 bcde 4.97 cd 9.83 bcde
35 11.53 abcd 5.49 def 10.17 bcd
70 12.80 abc 6.29 ab 14.60 a
105 12.04 abc 5.41 cd 14.23 a
150 0 10.62 cdef 5.29 cde 11.30 bc
35 10.63 cdef 5.33 cde 11.43 b
70 13.50 ab 6.52 a 14.33 a
105 13.86 a 6.26 ab 14.00 a
LSD (0.05) 2.45 0.69 1.63
CV (%) 14.28 7.03 9.22
LSD 0.05 = least significant difference at 5%, CV (%) = Coefficient of variation. Means in the
same column followed by the same letter(s) are not significantly different.
42

4.2.4. Number and weight of seeds per umbel
The number of seeds per umbel was significantly (P<0.01) affected due to the main effect of
applied nitrogen (N) and phosphorus (P) fertilizers. However, the interaction effect of N and
P did not influence number of seeds per umbel significantly (P>0.05) (Appendix Table 1).
Numerically the highest number of seeds per umbel was recorded for plants which received N
at a rate of 150 kg ha -1 which was statistically at par with 100 kg N ha -1 . The lowest number
of seeds per umbel was recorded from control treatments (Table 4). Application of N 150 kg
ha -1 brought about 26.88% increments in number of seed per umbel over control treatments.
Nitrogen has a great role that reduced the abortion of flowers on umbel, which might be
the reason for its effect on increasing seeds number per umbel (Marschner, 1995).
Similarly the effect of applied P significantly increased the number of seeds per umbel.
Numerically the highest number of seeds per umbel was recorded for plants which received P
at a rate of 105 kg P 2 O 5 ha -1 which was statistically at par with 70 kg P 2 O 5 ha -1 . The lowest
number of seeds per umbel was recorded from control treatments (Table 4). Application of P
at rate of 105 kg P 2 O 5 ha -1 brought about 37.17% increments in number of seed per umbel
over control treatments. Generally, increasing application rates of N and P fertilizers
increased the number of seed per umbel. This might be due to phosphorous has great effect of
on flower and seed production. This could possibly be due to the fact that these two important
plant nutrients might have complementary effect on retention of seed set per umbel.
Moreover, they are the major constituents of physiologically active organic compounds in the
plant system, leading to a combined increase in seeds number per umbel (Marschner, 1995)
This result was in line with Hossain et al. (2017) who reported the maximum number of
seeds per umbel (555.20) was found from 114 N and 42 kg P ha -1 and the minimum (494.00)
was from 57 N and 21 P kg ha -1 treatments. Kiros et al. (2018) the highest numbers of seeds
43

per umbel were recorded in plots which received 50, 75 and 100% of 69 kg N and 92 kg P 2 O 5
ha -1 fertilizer rates (825.3, 897 and 860 respectively) compared with unfertilized (675) plots
and lower rates (714.2). Getachew (2014) also reported that the highest number of seeds per
umbel (914.6) was recorded from plants which received 115 P 2 O 5 and 114 kg N ha -1 , and the
lowest from control treatments. Ali et al. (2007) who found that the highest number of seed
per umbel (95.28) was obtained from 150 kg N ha -1 and the lowest from the control. Tamrat
(2006) similarly reported the highest number of seeds per umbel (871) was recorded from 46
P 2 O 5 kg ha -1 and the lowest (825) from control. According to Debashis et al. (2017) nitrogen
175 kg ha -1 recorded significantly highest (744.34) number of seeds per umbel. At 50 kg P ha -
1 , the application of 50 or 100 kg N ha -1 gave significantly higher seed yield and seed weight
per umbel than other N and P rate combinations tested (Nwadukwe and Chude, 1995).
The analysis of variance revealed that significantly (P<0.01) differences were observed
among treatments in the main effect of nitrogen (N) and phosphorus (P) fertilizers on weight
of seed per umbel. Additionally the interaction effect of the two factors also had significant
influence on weight of seed per umbel (Appendix Table 1).
Numerically the highest weight of seeds per umbel was recorded from the combination of N
at the rate of 150 kg ha -1 with 105 kg P 2 O 5 ha -1 . This combination was statistically similar
when 100 kg N ha -1 combined with each of 70 and 105 kg P 2 O 5 ha -1 rates as well as when 150
kg N ha -1 combined with 35 kg P 2 O 5 ha -1 (Table 5). The lowest weight of seeds per umbel
was recorded for the combinations involving no N and P application levels. The application of
150 N with 105 kg P 2 O 5 ha -1 brought about 62.09% increments in weight of seeds per umbel
over the control. High seed weight per umbel under high N and P fertilizers might be due to
the role of nitrogen in the buildup of carbohydrate and different metabolites and the role of
phosphorous on seed formation and development. Nitrogen fertilization contributed toward
44

the seeds weight increment probably due to effect of nitrogen on increase leaf size and
assimilates partition to the seeds, thereby increased weight of seeds (Marschner, 1995).
The result was in agreement with Getachew (2014) and Ali et al. (2008) who reported that
seed weight per umbel was significantly increased by NP fertilizer 115 N kg ha -1 and 114
P 2 O 5 kg ha -1 and 150 N and 80 P 2 O 5 kg ha -1 applications, respectively. Debashis et al. (2017)
and Tamrat (2006) also reported the highest weight of seeds per umbel was obtained when N
was applied at a rate of 175 and 92 kg ha -1 followed by 125 and 138 kg ha -1 respectively.
Kiros et al. (2018) the highest seed weight per umbel was obtained from plants grown at 75%
of 69 kg N and 92 kg P 2 O 5 ha -1 fertilizer (3.02 g) and small seed weight (2.28 g) per umbel
was recorded from nil application of NP.
Table 4. Main effect of nitrogen and phosphorus fertilizers affected on number of flowers per
umbel and number of seeds per umbel onion seed grown at Kulumsa in 2017/2018.
Treatment
N (kg ha -1 )
Number of flowers per umbel
Number of
seed per umbel
0 302.23 b 722.71 c
50 357.27 b 821.78 b
100 459.06 a 945.16 a
150 426.73 a 977.8 a
LSD(0.05) 59.37 83.95
P 2 O 5 (kg ha -1 )
0 320.58 c 642.67 c
35 380.16 b 849.94 b
70 403.52 ab 952.0 a
105 441.03 a 1022.84 a
LSD(0.05) 59.37 83.95
CV (%) 18.43 11.61
LSD 0.05 = least significant difference at 5%, CV (%) = Coefficient of variation. Means in the
same column followed by the same letter(s) are not significantly different.
45

4.2.5. Seed yield per plant and per hectare
The analysis of variance revealed that significant (P<0.01) differences were exhibited for
seed yield per plant and per hectare due to main effect of nitrogen (N) and phosphorus (P) as
well as the interaction effect of two factors (Appendix Table 1).
The combinations of higher rates of both N (100 and 150 kg ha -1 ) and P (70 and 105 kg P 2 O 5
ha -1 ) resulted in better seed yield per umbel, seed yield per plant and seed yield per hectare.
Phosphorus fertilizer increased seed yield even without N fertilizer as compared to the control
treatments of no fertilizers at all. The lowest mean seed yield was recorded from control
treatments (Table 5). The combinations of 100 N with 105 P 2 O 5 kg ha -1 brought about
40.34% increments in seed yield per plant over the control. The combination of (100 N with
70 P 2 O 5 ) kg ha -1 brought about 57.72% increments in seed yield per hectare over the control.
In general, the seed yield showed an increasing trend with the combinations of higher N rates
with higher P 2 O 5 . The higher seed yield per plant may be due to the increase of
photosynthesis rate and translocation of food materials to seed.
The present study is in analogous with the findings of Hossain et al. (2017) the maximum
seed yield per plant (4.21 g) was recorded from 114 N and 42 P kg ha -1 and N 57 and P 21 kg
ha -1 treatment produced the minimum seed yield per plant (3.20 g). Debashis et al. (2017)
who indicated at Nitrogen 175 kg ha -1 recorded significantly highest seed yield per plant.
Tamrat (2006) also reported that seed yield per plant showed an increasing trend with the
combinations of N up to 92 kg ha -1 and P 2 O 5 up to 46 kg ha -1 and Nwadukwe and Chude
(1995) have reported that N rate at 50 or 100 kg ha -1 with P at 50 kg ha -1 increased seed yield
from 184 kg ha -1 to 226 kg ha -1 compared to the control treatment.
The most important components that affect onion seed yield are umbel size, flower stalk
diameter, flowers per umbel and number of flower stalks. However, umbel diameter was
46

noted to be the most important index for seed yield (Prats et al., 1996; Sidhu et.al., 1996;
Lemma and Shimelis, 2003). The correlation values of these components with seed yield in
the current study substantiated this fact. Number of seed per umbel (r = 0.70**), weight of
seed per umbel (r = 0.74**) were strong positive and highly significantly correlated with seed
yield per plant (Appendix Table 3).
In the present study, a balanced combination of macronutrient (NP) elements might have
increased seed yield of onion. The fact might be the fertilizer sufficiently supplied major plant
nutrients for vigorous growth and seed yield of onion.
Seed yield and yield characteristics increased with the increasing combinations or rate of
nitrogen and phosphorus fertilizers. This could be due to increases the availability of nutrients
considerably resulting in positive effect of growth parameters. This is also because of the
synergetic effects of N and P on yield. If there is a balance supply of N and P, the effect is
always synergetic for seed yield. Nitrogen is so vital because it is a major component of
chlorophyll, the compound by which plants use sunlight energy to produce sugars from water
and carbon dioxide (i.e., photosynthesis). It is also an essential nutrient for plant growth,
development and reproduction and a major component of amino acids, the building blocks of
proteins. Phosphorus in plants, improved flower formation and seed production, more
uniform and earlier crop maturity, increased N-fixing capacity, improvements in crop quality,
increased resistance to plant diseases, supports development throughout entire life cycle. This
very important character increased by P application probably due to the fact that this element
was vital for flowering, seed formation and related reproductive activities (Brady and Weil,
2002). Increase in growth parameters might have facilitated quick and greater availability of
plant nutrients and thus provide a better environment for better reproductive growth. In
present investigation all the components contributing indirectly and directly towards yield viz.
vigorous vegetative growth, number of flower stalks per plant, number and weight of seeds
47

per umbel, seed yield per plant and also seed weight per hectare were superior in the
treatment with higher rates of both N and P 2 O 5 combinations.
The results of present study seem to imply that significant yield increment is possible with
increasing application of N and P. The increased seed yield by N fertilization might be due to
the fact that the plant uptake of N and the resultant growth increment that increased almost all
yield components as revealed in the relationship of these yield components and the obtained
yield per plant and hectare (Appendix Table 6). The seed yield obtained by the interaction
effect greater than the main effect of two nutrients might be due to the fact that addition of N
along with P enhanced markedly the uptake of soil N and P thereby acting and affecting
jointly the seed yield per plant. In addition, this study showed that the seed yield per hectare
was directly dependent on seed yield per plant. The highest seed yield per plant gave highest
seed yield per hectare. Positive and highly significant correlation values between seed yield
per plant and hectare (r = 0.94**) expressed how they were strongly correlated (Appendix
Table 3) supported with the findings of Tamrat (2006), Getachew (2014) and Debashis et al.
(2017).
In the present study higher yield was recorded as compared to other reports in Ethiopia may
be because of the reason that at kulumsa is conducive for onion seed production (cool
climate) and the rainfall was uniform during bolting and flowering stage.
The current result was in accordance with the findings of Hossain et al. (2017) the maximum
seed yield per hectare (957.6 kg) was found from 114 N and 42 kg P ha -1 and the minimum
seed (776.6 kg) was observed from 57 N and 21 P kg ha -1 treatments. Getachew (2014) who
reported the highest seed yields per plot and per hectare were obtained from plants that
received 115 P 2 O 5 and 114 kg N ha -1 . According to Debashis et al. (2017) nitrogen at 175 kg
ha -1 recorded significantly highest seed yield per hectare. Ali et al. (2008) phosphorous
48

fertilization increased seed yield per umbel, per plot and per hectare. The application of
nitrogen at 92 Kg N ha -1 in split doses and phosphorus at 46 kg P 2 O 5 ha -1 appeared to be a
promising combination with seed yield increment of about 42% over unfertilized seed onion
crop (Lemma and Shimeles, 2003; Dawit et al., 2004; Tamrat, 2006; Abdissa et al., 2011).
Table 5. The interaction effect of N and P fertilizers on seed yield per umbel, seed yield plant
and seed yield per hectare grown at Kulumsa in 2017/2018.
N (kg ha -1 ) P 2 O 5 (kg ha -1 ) Seed yield
umbel -1 (g)
Seed yield
plant -1 (g)
Seed yield ha -1
(kg)
0 0 1.52 h 6.73 g 785.33 f
35 2.11 gh 7.91 ef 1093.55 e
70 2.58 fg 8.63 de 1454.11 cd
105 2.67 efg 7.81 efg 1175.83 e
50 0 1.59 h 6.8 fg 1053.33 e
35 2.89 def 7.54 efg 1196.57 e
70 2.93 cdef 9.53 cd 1412.98 cd
105 3.25 bcde 10.17 abc 1660.68 b
100 0 2.54 fg 7.84 efg 1126.73 e
35 2.91 cdef 8.69 de 1394.38 d
70 3.67 ab 10.82 ab 1858.82 a
105 3.56 abc 11.28 a 1740.65 ab
150 0 2.19 gh 7.78 efg 1162.69 e
35 3.39 abcd 9.71 cde 1591.40 bc
70 3.03 bcdef 10.21 abc 1700.45 ab
105 4.05 a 10.02 bc 1671.68 ab
LSD(0.05) 0.67 1.17 188.69
CV (%) 13.59 7.97 8.22
LSD 0.05 = least significant difference at 5%, CV (%) = Coefficient of variation. Means in the
same columns with the same letter(s) are not significantly different.
49

4.3. Seed Quality Parameters
4.3.1. Thousand seeds weight
The main effect of phosphorus (P) significantly (P<0.05) affected 1000 seeds weight.
However, nitrogen (N) and its interaction with P did not significantly (P>0.05) affect 1000
seed weight (Appendix Table 1).
The highest 1000 seeds weight was obtained from plants which received P fertilizer 70 kg
P 2 O 5 ha -1 . Plants which did not receive fertilizer produced the lowest 1000 seeds weight
which in fact, was not significantly different from 1000 seeds weight at 105P 2 O 5 (Fig. 5).
Application of 70 P 2 O 5 kg ha -1 brought by about 9.73% increments in 1000 seed weight over
the control treatments.
Phosphorus in plants, improved flower formation and seed
production, more uniform and earlier crop maturity, increased N-fixing capacity,
improvements in crop quality, increased resistance to plant diseases, supports development
throughout entire life cycle and it is actively involved as building block of the seed materials
there by increased the weight of the seed of the onion crop (Brady and Weil, 2002).
In agreement with the present study Ozer (2003), Ozden (2009) and Getachew (2014)
reported that higher rates of fertilizers application produced heavy weight seeds. On the other
hand, the current study results were in contrast to Tamrat (2006), Ali et al. (2007) and Ali et
al. (2008) who reported that phosphorous fertilizers did not have significant effect on 1000
seed weight. The maximum weight (3.42 g) was gained from 114 N and 42 P kg ha -1
treatments and the minimum (3.18 g) was from 57 N and 21 P kg ha -1 treatments (Hossain et
al., 2017)
50

Figure 5. The main effect of phosphorus (P) fertilizer affected 1000 seed weight of onion at
kulumsa in Arsi Zone, South Eastern Ethiopia in 2017/2018.
4.4.2. Percentage of seed germination one month later after harvest
Germination percentage was significantly affected by the main effects of both N (P<0.05) and
P (P<0.01) fertilizers, but the interaction effect of the two factors did not show significant
(P>0.05) difference (Appendix Table 1).
Numerically the highest seed germination 30 days after harvest was recorded from the rate of
N application at 100 kg ha -1 which was statistically similar with 150 kg N ha -1 . The lowest
seed germination was recorded from non fertilized plots (Fig.6A).
Similarly the application of P fertilizer significantly (P<0.01) increased the germination 30
days after harvest. Numerically the highest germination percentage was obtained from the
application of P at a rate of 105 kg P 2 O 5 ha -1 followed by 70 kg P 2 O 5 ha -1 . The lowest seed
germination was recorded from non fertilized plots. Generally, as the rate of P increased
percent of seed germination 30 days after harvest was increased (Fig.6B).
In agreement with the present study to Debashis et al. (2017) who reported that the highest
germination percentage of harvested seed was observed in treatment received 175 kg N ha -1 .
51

Tamrat (2006) and Ali et al. (2007) also reported that phosphorous and nitrogen fertilization
had significant effect on seed germination percentage in which mostly higher germination
percentage was recorded from high fertilizer application. Application of 143.6 P 2 O 5 and 142.5
N kg ha -1 fertilizers gave highest germination percentage of onion seeds (Getachew, 2014).
Percent of seed germination increased with an increase of nitrogen fertilization from control
(Ali et al., 1998)
Figure 6. Percent of seed germination affected by the main effect of nitrogen (A) and
phosphorus (B) fertilizers on onion plant at kulumsa in Arsi Zone, South Eastern Ethiopia in
2017/2018.
4.4. Correlation Analysis of Agronomic and Yield Components
Correlation coefficient values (r) were computed to display the relationships between and
within agronomic parameter of seed onion crop. Correlation coefficient was calculated for the
different response variables which help to show how the yield components and growth
characters affect the seed yield of onion (Appendix Table 3).
Days to bolting was highly significantly correlated with days to flowering (r = 0.75**) and
days to maturity (r = 0.56**). Thus, the result implied that increase in days to bolting result in
increasing days to flowering and onion seed maturity. This finding is similar with the result of
Tamrat (2006).
52

Umbel diameter of the onion was positively and significantly correlated with number of seed
per umbel (r = 0.5**), seed yield per plant (r = 0.43**) and seed yield per hectare (r =
0.56**). This result similarly implied that the increment of umbel size causes for the
increment of number of seed per umbel and seed yield per plant and per hectare. This result is
in accordance with the findings of Prats et al. (1996), Sidhu et al. (1996) and Tamrat (2006).
Positive and statistically highly significant correlation was also observed between seeds
number per umbel and weight of seeds per umbel (r = 0.92**). Similarly seed yield per plant
directly and highly significantly related with number of umbels per plant (r = 0.56**), number
of seeds per umbel (r = 0.70**), weight of seeds per umbel (r = 0.74**) and umbel diameter
(r = 0.43**) (Appendix Table 3). Seed yield per hectare positively and statistically highly
significant correlated with all yield and yield components, but negatively and not significantly
correlated with phenology and growth parameters. As stated by Prats et al. (1996), Sidhu et
al. (1996) and Tamrat (2006) umbel diameter was major determining factor for seed yield.
This indicated that this character could be the most important index for seed yield.
In harmony with results of the present study Prats et al. (1996), Sidhu et al. (1996) and
Tamrat (2006) also indicated that the higher seed yield in onion cultivars was due to the
higher number of seed stalks per plant and to a wider umbel diameter which were influenced
by application of N and P fertilizers.
4.5. Concentration of Nitrogen (N) and Phosphorus (P) in Soils after Harvest
4.5.1. Total nitrogen concentration in soil
The main effects of nitrogen (N) and phosphorus (P) fertilizers as well as the interaction
effects of the two factors significantly (P<0.01) affected total N in the soil after harvest
(Appendix Table 2).
53

The treatment combinations of the applied N at rate of 100 kg ha -1 with 70 kg P 2 O 5 ha -1
revealed numerically the highest N concentration in the soil. Total N in the soil after harvest
was high when P 2 O 5 was applied at higher rates in combinations of N as well as no N
fertilizer. This indicated that P fertilizer increased availability of N from the soil pool. The
lowest N concentration of soil recorded from control treatments (Table 6). The pre sowing
level of N (0.18%) (Appendix Table 7) of the soil decreased to 0.130% in the control and it
was in the range of 0.130 to 0.187% in plots applied with N and P after harvest. This
reduction of total N in the soil after harvest in control plot was might be due to the
consumptive use of the crop, it is because of zero addition of N and P fertilizers in the soil
and the plant consumed what was available there.
4.5.2. Available phosphorus concentration in soils
The main effects of nitrogen (N) and phosphorus (P) fertilizers as well as their interaction
effects of the two factors significantly (P<0.01) affected available P concentration of soil after
harvest (Appendix Table 2).
Numerically the highest available P of the soil was recorded when N at a rate of 150 kg N ha -1
applied with 70 kg P 2 O 5 ha -1 which was statistically at par with the combination of 100 kg N
ha -1 with 70 kg P 2 O 5 ha -1 . The lowest available P of soil was recorded from control treatments
(Table 6). The available P concentration of the soil before planting which was 5.42 ppm was
increased up to 10.96 ppm due to application of N and P fertilizers. The initial level of
available P of the soil decreased to 4.11ppm in the control treatments, which implied that
some of the soil P was lost through either plant uptake or fixation in the soil. The combination
of N and P fertilization resulting in increment of available P in the soil in this study may be
due to its replacement of already fixed P and increase the levels in the soil and particularly its
level in the labile forms that can release phosphorus to the soil solution. It is clear that N
54

application increased availability of P after harvest (Table 6). Most of the P present in soils is
in unavailable forms and added soluble forms of P are quickly fixed by many soils (Tisdale et
al., 1995). In agreement with the report of Tamrat (2006) and Brady and Weil (2002)
indicated that fixation is the major loss of available soil phosphorus.
Table 6. The interaction effect of nitrogen (N) and phosphorus (P) fertilizers on Concentration
of total nitrogen (%) and available P in the soil after harvest in 2017/2018.
N(kg ha -1 ) P 2 O 5 kg ha -1 Total N% Available P (ppm)
0 0 0.130 f 4.11 h
35 0.153 ed 6.09 fg
70 0.170 abcd 7.36d ef
105 0.173 abc 8.19 cd
50 0 0.170 abcd 6.74 efg
35 0.170 abcd 5.73 g
70 0.160 cde 7.41 de
105 0.150 e 9.29 bc
100 0 0.180 ab 6.61 efg
35 0.180 ab 7.25 def
70 0.187 a 10.15 ab
105 0.170 abcd 9.51 b
150 0 0.163 bcde 7.62 de
35 0.177 abc 9.90 ab
70 0.180 ab 10.96 a
105 0.180 ab 9.55 b
LSD(0.05) 0.017 1.308
CV (%) 6.13 9.95
LSD 0.05 = least significant difference at 5%, CV (%) = Coefficient of variation. Means in the
same columns followed by the same letter(s) are not significantly different.
55

4.6. Nutrient Accumulation of N and P in Plant Tissues and Their Uptake of Onion
Plants
4.6.1. Nitrogen concentration in plant tissues
Concentration of N in the leaves and seeds of onion were affected significantly (P<0.01) the
main effect of nitrogen (N) and phosphorus (P) fertilizer as well as the interaction of the two
factors (Appendix Table 2).
The highest concentration of N in leaves was recorded due to the combination of 150 kg N ha -
1 with 70 kg P 2 O 5 ha -1 which was statistically at par applied 100 kg N ha -1 with P 70 kg P 2 O 5
ha -1 . The lowest concentration of N in onion leaves recorded from non fertilized plots (Table
8).
Numerically the highest concentration of N in seed was recorded in the combination of 100
kg N ha -1
with 70 kg P 2 O 5 ha -1 . However, these combination of N and P resulted in
statistically similar effect with 50 or 150 kg N each combined with 70 or 105 kg P 2 O 5 ha -1 as
well as when 100 kg N was combined with 35 kg P 2 O 5 ha -1 . The lowest concentration of N in
onion seed recorded from non fertilized plots (Table 8). In general, the P fertilizer increased
the concentration of N in seeds also increased without N fertilizer, but not increased the
concentration of N in leaves. This result was in accordance with Tamrat (2006) who reported
that the highest N concentration in the leaves and seeds were recorded in the application of N
at rate of 138 kg ha -1 of N and 69 kg P 2 O 5 ha -1 of P fertilization and lowest from control plots.
4.6.2. Phosphorus concentration in plant tissues
The concentration of P in onion leaves and seeds are significantly (P<0.01) affected the main
effect of nitrogen (N) and phosphorus (P) fertilizers. However, their interaction was not
significant (P>0.05) (Appendix Table 2).
56

The highest P concentrations in leaves were recorded the main effect of N and P at the rate of
100 and 150 kg N ha -1 and 70 and 105 kg P 2 O 5 ha -1 ; however the difference between these
two treatments were not significant. The lowest concentration of P in leaves was recorded
from the control treatments (Table 7).
The main effect of N and P significantly affected P concentration of seeds. The interaction of
these two fertilizers (N and P) did not affect P concentrations in the seed. All N rates were
significant in P concentration in plant tissues. The highest P concentration in seed at the rate
of 150 kg N ha -1 which was followed by100 kg N ha -1 . The lowest concentration of P in seed
was recorded at the control treatments which was not significant with 50 kg N ha -1 (Table 7).
This result was in line with Debashis et al. (2017) the maximum concentration of onion seed
N (0.65 %), P (0.035 %) was recorded with the application of nitrogen 175 kg ha -1 .
Similarly, main effect of P fertilizer application showed the highest P concentrations of seed
at 105 kg P 2 O 5 ha -1 followed by both at 35 and 70 kg P 2 O 5 ha -1 . The lowest concentration of P
in seed was recorded from control treatments (Table 7). Phosphorus concentrations of both
leaves and seeds consistently increased with increasing rates of N and P fertilizers. Plants
provided with adequate amount of phosphorus forms good root system, thus enabling plants
to explore nutrient in the soil and absorb, then consequently the concentration of the element
becomes high in the tissues (Thaler and Pages, 1998). This might be the case for increment in
P concentration in onion crop in this study. Similarly, nitrogen might have influenced the
concentration of the two elements due to its increasing amount added to the soil and
accessible for absorption. The abundant availability of these two nutrients directly responsible
to increase in their concentration in the tissues of the crop. Generally, nitrogen fertilizer
application helps the availability of nitrogen in the soil and uptake of N and its concentration
in the tissues, these increase with increasing applied N and P rates (Kumar and Rao, 1992;
Panda et al., 1995; Tamrat, 2006)
57

The present study was in line or in accordance with the findings of Tamrat (2006) the highest
P concentration of the onion seeds was recorded at the rate of 46 and 69 kg P 2 O 5 ha -1 . For
most plant species, the total P concentration of healthy leaf tissue is not high, usually
comprising only 0.2 and 0.4% of the dry matter (Brady and Weil, 2002).
Table 7. Phosphorus conc. in plant tissues affected by the main effect of nitrogen and
phosphorus fertilizers grown at Kulumsa in 2017/2018.
Treatments P conc. in plant tissues (%)
N (kg ha -1 ) in leaves in seed
0 0.023 b 0.134 c
50 0.024 b 0.137 c
100 0.031 a 0.155 b
150 0.029 a 0.162 a
LSD ( 0.05) 0.003 0.006
P 2 O 5 (kg ha -1 )
0 0.022 c 0.136 c
35 0.026 b 0.147 b
70 0.029 a 0.147 b
105 0.031 a 0.158 a
LSD ( 0.05) 0.003 0.006
CV (%) 12.82 5.03
LSD 0.05 = least significant difference at 5%, CV (%) = Coefficient of variation. Means in the
same columns followed by the same letter(s) are not significantly different.
4.6.3. Nitrogen uptake by leaves and seeds
The main effect of nitrogen and phosphorus fertilizers significantly (P<0.01) affected the N
uptake of the onion plant. The interaction between applied N and P had significant effect on N
uptake by seeds, but leaves and whole plant was not significant (P>0.05) (Appendix Table 2).
Nitrogen uptake by leaves was affected by N fertilization. Numerically the highest N uptake
was observed at rate of 150 kg N ha -1 which was statistically at par with N at rate of 100 kg
58

ha -1 . The lowest N uptake of leaves was recorded from control treatments (Table 9). El Hilo et
al. (1970) who reported the higher nitrogen fertilizer application resulted in high total
nitrogen concentrations in the leaves. The present results in agreement with Tamrat (2006)
who reported that the N uptake increased with increasing levels of applied N from 32.60 at
control to 84.09 kg ha -1 at applied N rate of 138 kg ha -1 . Nitrogen accumulation by the onion
leaves was increased by N fertilization with the 224 kg ha -1 N rate having significantly higher
N accumulation (32.1 kg N ha -1 ) than the 0 and 45 kg ha -1 N rates (27.6 and 29.4 kg N ha -1 ,
respectively) (Ardell et al., 2008)
Application of P fertilizer consistently increased the uptake of N by leaves. The application of
P at the rate of 105 kg P 2 O 5 ha -1 gave the highest N uptake which was statistically at par with
P at rate of 70 kg P 2 O 5 ha -1 . The lowest one was recorded from control treatments (Table 9).
The present results in agreement with the report of Tamrat (2006) P at the rate of 69 kg P 2 O 5
ha -1 gave the highest N uptake (87.95 kg ha -1 ) followed by the application of 46 kg P 2 O 5 ha -1 ,
but they were not significant difference between them.
The interaction effect of nitrogen (N) and phosphorus (P) fertilizers resulted in significant
(P<0.01) differences was recorded in N uptake of seeds (Appendix Table 2). The highest N
uptake of seed observed in plants that received a combinations of 100 kg N ha -1 with 70 kg
P 2 O 5 ha -1 followed by 150 kg N ha -1 with each of 70 and 105 kg P 2 O 5 ha -1 rates as well as
when 50 kg N ha -1 combined with 105 kg P 2 O 5 ha -1 . The lowest N up take of seed was
recorded from control treatments (Table 8). The uptake and utilization of N in any form vary
among plant species and varieties, but the general trend is that the plant uptake of N and the
resultant growth and yield are increased as the result of increasing the soil nitrogen. At low
level of N availability, uptake and tissue concentration of N become low and the yield is
proportional to N uptake in grain (Borrell et al., 1998).
59

This result was in accordance with the findings of Debashis et al. (2017) reported that the
maximum uptake of onion seed N was recorded with the application of the higher nitrogen
fertilizer. Tamrat (2006) also reported that the highest N uptake of seed observed in plants
that received a combination of 138 kg N ha -1 and 69 kg P 2 O 5 ha -1 .
4.6.4. Whole plant nitrogen uptake
The whole plant N uptake was significantly (P<0.01) affected by the main effect of nitrogen
(N) and phosphorus (P) fertilizers. However, the interaction effect was not significant
(P>0.05) (Appendix Table 2).
Regarding to N fertilizer application rates at 150 kg N ha -1 recorded for the highest N uptake
which was statistically at par with N at rate of 100 kg ha -1 . The lowest N uptake was observed
in plants that were not fertilized with N (Table 9). The P application rates also showed
significant difference on N uptake of the plant. The highest N uptake was recorded at the
application of 105 kg P 2 O 5 ha -1 which was statistically at par with 70 kg P 2 O 5 ha -1 . The lowest
was recorded from the control treatments (Table 9). In general, the result showed a consistent
increment of N uptake by whole plant with the increment of P fertilizer application. This
increment of whole plant uptake of N by N and P fertilization might be due to the fact that
nitrogen and phosphorus fertilizer application increase P and N uptake from the soil (Borrell
et al., 1998). In a soil with high P, there was a direct correlation between the N and P uptake
of other crops and onion as reported by (Kumar and Rao, 1992; Panda et al., 1995; Tamrat,
2006). They indicated increasing N and P uptake with increasing N and P fertilizer levels in
the soil as a result of improved availability and uptake through increased root growth and
effective absorption. The plant uptake of nutrients followed similar pattern as the leaves and
seeds because the plant uptake was the sum of the two.
60

The present result is in line with Tamrat (2006) who reported that N fertilizer application rates
at 138 kg N ha -1 recorded for the highest N uptake 85.98 kg N ha -1 and highest 89.98 kg N ha -
1 uptake was recorded at the application rate of 69 kg P 2 O 5 ha -1 and the lowest at the control
treatment. Application of the highest level of nitrogen fertilizer (150 kg N) produced the
highest values of yield, quality and nutrients uptake (279.3 mg plant -1 ) characters of onion
crops (El-Hadidi et al., 2016).
4.6.5. Phosphorus uptake by leaves and seeds
Phosphorus uptake of onion leaves was influenced significantly (P<0.01) due to nitrogen (N)
and phosphorus (P) fertilization, but their interaction did not show significant (P>0.05) effect
(Appendix Table 2). The application of N fertilizer brought significant difference in P uptake
of the leaves at different rate of N fertilizer. The highest P uptake of leaves was obtained at a
rate of 150 kg N ha -1 which was statistically at par with 100 kg N ha -1 . The lowest uptake was
recorded from control treatments (Table 9). Similar results were recorded with Tamrat (2006)
the highest P uptake (2.317 kg P ha -1 ) was obtained at 138 kg N ha -1 and the lowest (0.61 kg P
ha -1 ) uptake at no N fertilizer application.
Application of P fertilizer at varying levels increased the P uptake of leaves. The highest
uptake was recorded at the rate of 105 kg P 2 O 5 ha -1 followed by 70 kg P 2 O 5 ha -1 which was
statistically at par with the former. The lowest uptake was recorded on plot with no
application of P fertilizer (Table 9). The present results in line with Tamrat (2006) the highest
uptake (2.464 kg P ha -1 ) was recorded at the rate of 69 kg P 2 O 5 ha -1 and lowest (0.865 kg P ha -
1 ) uptake was recorded on plot with no application P fertilizer.
Phosphorus uptake of onion seed was influenced significantly (P<0.01) due to nitrogen (N)
and phosphorus (P) fertilization. The interaction of these two factors also resulted in
significantly (P<0.05) influenced (Appendix Table 2).
61

Numerically the highest P uptake of the seed was recorded when 100 kg ha -1 N was combined
with each of 70 and 105 kg P 2 O 5 ha -1 which was statistically at par with the combination of
150 kg N ha -1 with each of 70 and 105 kg P 2 O 5 ha -1 . The lowest P uptake by seed was
recorded at the control with no N and P fertilizer application (Table 8). In general, as the
combination of nitrogen and phosphorus fertilizers rates increased P uptake of seed increases.
The present result was in accordance with Tamrat (2006) who reported that the highest P
uptake of the seed was recorded at the rate of 69 kg P 2 O 5 ha -1 of P application. Debashis et al.
(2017) higher levels of nitrogen which in turn resulted in higher uptake of N and P onion seed
crop.
Table 8. Interaction effects of N and P fertilizers on nitrogen concentration in leaves, seed
and up take in seed grown at Kulumsa in 2017/2018.
N (kg ha -1 ) P 2 O 5 (kgha -1 ) N conc.
leaves (%)
N conc.
Seed (%)
N uptake of
seed(kg ha -1 )
P uptake of
seed(kg ha -1 )
0 0 0.483 g 0.633 e 0.270 h 0.054 i
35 0.637 ed 0.833 d 0.408 g 0.062 ghi
70 0.493 g 0.967 bc 0.616 e 0.088 de
105 0.580 f 0.940 c 0.495 f 0.083 ef
50 0 0.570 f 0.857 d 0.404 g 0.058 hi
35 0.590 f 0.850 d 0.456 fg 0.072 ghi
70 0.590 f 0.980 abc 0.620 e 0.085 def
105 0.700 abc 0.980 abc 0.729 bc 0.108 bc
100 0 0.690 abc 0.973 bc 0.517 f 0.074 efg
35 0.600 ef 0.997 abc 0.623 e 0.099 cd
70 0.707 ab 1.050 a 0.874 a 0.131 a
105 0.637 de 0.810 d 0.631 de 0.125 a
150 0 0.610 ef 0.990 abc 0.516 f 0.077 efg
35 0.660 cd 0.973 bc 0.694 cd 0.119 ab
70 0.727 a 1.003 abc 0.764 b 0.124 a
105 0.667 bcd 1.020 ab 0.765 b 0.128 a
LSD(0.05) 0.042 0.0747 0.067 0.016
CV (%) 4.09 4.82 6.86 10.12
LSD 0.05 = least significant difference at 5%, CV (%) = Coefficient of variation. Means in the
same columns followed by the same letter(s) are not significantly different.
62

4.6.6. Whole plant phosphorus uptake
The P uptake of onion plant was significantly (P<0.01) influenced by the application of
nitrogen (N) and phosphorus (P), but the interaction effect of the two fertilizers did not show
significant (P>0.05) (Appendix Table 2).
The whole plant uptake of P increased highly with the increasing rate of both N and P
fertilizers. Numerically the highest P up take of plant was recorded from N at rate of 150 kg
ha -1 but not significant difference with 100 kg ha -1 . The lowest P uptake of whole pant was
recorded from control treatments (Table 9). The present result was in accordance with Tamrat
(2006) the highest P uptake by plant 2.514 kg ha -1 was recorded at the rate of 138 kg N ha -1
and the lowest 0.711 kg ha -1 at the control. A good supply of nitrogen stimulates root growth
and development as well as the uptake of other nutrients (Brady and Weil, 2002).
The highest P uptake was recorded at 105 kg P 2 O 5 ha -1 which was not significantly different
from P at rate of 70 kg P 2 O 5 ha -1 . The lowest P uptake by the whole plant was recorded from
control treatments (Table 9). According to Mengel and Kirkby (1987) the nutrient content of
plant tissue reflects soil availability. The movement of phosphorus in soils is very low and its
uptake generally depends on the concentration gradient and diffusion in the soil near roots
(Mcpharilin and Robertson, 1999). The low P uptake and concentrations in plant materials of
the control might therefore be attributed to moderate P availability in the experimental soil; as
was also confirmed by soil analysis before planting (Appendix table 7). The present study
showed that application of N and P fertilizer significantly increased the uptake of P in leaves,
seed and the whole plant. This might be due to their increased availability of P by the
application of fertilizer to the soil, their subsequent effective absorption, utilization and
development of different structure of the plant that help them increase uptake of the nutrients
from the soil.
63

This result is in harmony with Tamrat (2006) who reported the highest P uptake 2.67 kg P ha -
1 recorded at 69 kg P 2 O 5 ha -1 and the lowest 0.989 kg ha -1 P uptake by the whole plant was
recorded from control treatments. Application of the highest level of phosphorus fertilizer 100
kg P 2 O 5 produced the highest values of yield, quality and nutrients uptake 262.2 mg plant -1
characters of onion crops (El-Hadidi et al., 2016). Nitrogen fertilizer application improves
phosphorus uptake from the soil (Kumar and Rao, 1992; Panda et.al., 1995). Nutrient
efficient plants produce high yield with low uptake of nutrients (Fageria et al., 2015).
Table 9. The main effect of nitrogen (N) and phosphorus (P) fertilization affected on plant
uptake of N and P (kg ha -1 ) at kulumsa in 2017/2018.
Plant up take of N(kg ha -1 ) Plant up take of P (kg ha -1 )
N (kg ha -1 ) Leaves Seed Whole plant Leaves Seed Whole plant
0 30.729 b 0.447 c 31.176 b 1.277 b 0.072 c 1.357 b
50 33.109 b 0.552 b 33.662 b 1.347 b 0.08 b 1.419 b
100 41.528 a 0.661 a 42.190 a 1.996 a 0.107 a 2.103 a
150 44.414 a 0.685 a 45.099 a 2.026 a 0.112 a 2.138 a
LSD(0.05) 4.419 0.0345 4.419 0.272 0.008 0.272
P 2 O 5 (kg ha -1 )
0 31.759 b 0.427 d 32.186 b 1.208 b 0.066 c 1.274 b
35 33.882 b 0.545 c 34.427 b 1.421 b 0.088 b 1.509 b
70 41.099 a 0.719 a 41.818 a 1.965 a 0.107 a 2.072 a
105 43.040 a 0.655 b 43.695 a 2.052 a 0.111 a 2.163 a
LSD(0.05) 4.419 0.0345 4.419 0.272 0.008 0.272
CV (%) 14.16 7.06 13.93 19.62 10.22 18.60
LSD 0.05 = least significant difference at 5%, CV (%) = Coefficient of variation. Means in the
same columns followed by the same letter(s) are not significantly different.
64

4.7. Nutrient Use Efficiency (NUE)
4.7.1. Agronomic efficiency (AE) of nitrogen and phosphorus
The agronomic efficiency of N fertilizer was significantly (P<0.01) influenced by the main
effects of nitrogen (N) and phosphorus (P) fertilizers as well as their interaction effects of the
two factors (Appendix Table 2).
The highest agronomic efficiency of N fertilizer was recorded from N at a rate of 50 kg ha -1
which was followed by N at rate of 100 kg ha -1 . Numerically the lowest agronomic efficiency
was recorded from the higher application of N at rates of 150 kg ha -1 . Generally, as N rates
increases the agronomic use efficiency was decreased (Table 10). The application of N
fertilizers, agronomic efficiency decreases with increasing fertilizer rates supply due to the
opposite relationship between increasing nutrient supply and yield production.
Application of P fertilizer consistently increased the agronomic efficiency of N. The highest
agronomic efficiency of N was recorded from P at a rate of 105 kg P 2 O 5 ha -1 which was
followed by P at rate of 70 kg P 2 O 5 ha -1 . Numerically the lowest agronomic efficiency of N
was recorded from the lower application of P at rates of 35 kg P 2 O 5 ha -1 . Generally, as P rates
increases the agronomic efficiency was consistently increased (Table 10).
The agronomic efficiency of P fertilizer was significantly (P<0.01) influenced by the main
effects of nitrogen (N) and phosphorus (P) fertilizers as well as their interaction effects of the
two factors (Appendix Table 2).
Numerically the highest agronomic efficiency of P was recorded from N at a rate of 150 kg
ha -1 which was statistically at par with N at rate of 100 kg ha -1 . The lowest agronomic
efficiency of P was recorded from the lower application of N at rates of 50 kg ha -1 . Generally,
as N rates increases the agronomic efficiency of P was consistently increased (Table 10).
65

Similarly the application of P fertilizer affected agronomic efficiency of P. Numerically the
highest agronomic efficiency of P was obtained from P at a rate of 35 kg P 2 O 5 ha -1 which was
followed by P at rate of 70 kg P 2 O 5 ha -1 .The lowest agronomic efficiency of P was recorded
from the higher application of P at rates of 105 kg P 2 O 5 ha -1 . Generally, as P rates increases
the agronomic use efficiency was consistently reduced (Table 10).
The reason of P use efficiency tended to be greater in to those treatments receiving optimum
rates, the crops used wisely in P 2 O 5 . These improvements in NUE reflect greater capture and
use of N for growth and P for seed formation though overall yield was reduced by N and P
limitations. N and P use efficiency decreased linearly as more N and P 2 O 5 introduced in to the
fertilizer mix or combined. This effect was primarily to a reduction of N and P use efficiency
as a proportion of N and P 2 O 5 increased and reflects the N leaching losses and P fixation that
occurred with soluble N and P fertilizers (Drost et al., 2002).
Nitrogen use efficiency (NUE) decreased significantly with increasing N rate when expressed
as a function of total N uptake and available N. The interaction resulted from greater NUE
differences between at the lower N rates than at the higher N rates (Ardell et al., 2008).
Halvorson et al. (2002) reported that N fertilizer use efficiency (NFUE) by onion to be about
15%. High agronomic efficiency would be obtained if the yield increment per unit applied is
high (Roberts, 2008), nevertheless what amount can be considered as high agronomic
efficiency is not exactly identified. According to Fageria et al. (2015) an efficient plant is one
that produces higher economic yield with a limited quantity of applied or absorbed nutrient.
Agronomic efficiency of N more than threefold was reported by Banerjee et al. (2015) from
the lower levels of N fertilization as compared to the higher levels. This was due to the fact
that input-output relationship follows the law of diminishing return as far as the relationship
between N and yield is concerned (Das et al., 2015). Similar results recorded to potato crops
AE of phosphorus were reported by Salam et al. (2014) and Sandana (2016) when P supplied
66

from organic and inorganic sources and the authors stated that AE of phosphorus decreased
when P fertilization increased. Sammis (1997) reported the need for high rates of N on onion
to optimize yield in New Mexico, but expressed concern about leaching of NO - 3 N from the
root zone and the low NFUE (30%) by onion.
4.7.2. Physiological efficiency (PE) of nitrogen and phosphorus
Physiological efficiency of N fertilizer was highly significant (P<0.01) due to main effect of
nitrogen (N), but phosphorus fertilizers did not. However, their interaction effects of the two
factors significantly (P<0.05) affected physiological efficiency (Appendix Table 2).
Numerically the highest physiological efficiency of N was recorded from N at a rate of 50 kg
N ha -1 which was statistically similar with N at a rate of 100 kg ha -1 . The lowest physiological
efficiency of N was recorded from the higher application of 150 kg N ha -1 (Table 10). The
lowest physiological efficiency might indicate that the crop did not utilize the absorbed N for
the production of maximum seed yield. Furthermore, increasing the N to 100 kg N ha -1 the
nutrient levels may lead to decreased in physiological efficiency. This suggests that higher
nutrient addition (above optimum level) excessive results in luxury nutrient uptake that might
not contribute to physiological processes. It may be due to the application of excess nutrients,
which was not effectively utilized by the crop and the rate of production was lesser per unit of
nutrients application (Senthil et al., 2008). Interrelated finding on potato reported by Banerjee
et al. (2015) indicated that at high uptake of N the physiological efficiency was decreases.
Physiological efficiency of P fertilizer was highly significant (P<0.01) due to main effect of
phosphorus (P) rates, but nitrogen fertilizers and their interaction did not (Appendix Table 2).
Numerically the highest physiological efficiency of P was recorded from P at a rate of 70 kg
P 2 O 5 ha -1 which was statistically similar with P at a rate of 105 kg P 2 O 5 ha -1 . The lowest
physiological efficiency of P was obtained from the lowest application of 35 kg P 2 O 5 ha -1
67

(Table 10). The lowest physiological efficiency might indicate that the crop did not utilize the
absorbed P for the production of maximum seed yield. The present result also agreement with
the other crops reported that the efficient in nutrient utilization to produce a high yield with
low absorbed nutrient, in a soil that is limiting in one or more mineral nutrients (Fageria et al.,
2015; Marschner, 1993).
4.7.3. Apparent recovery (AR) of nitrogen and phosphorus
Apparent recovery of N was significantly (P<0.01) affected the main effect of nitrogen (N)
and phosphorus (P) as well as the interaction effect of the two factors (Appendix Table 2).
Numerically the highest apparent recovery of N was obtained from N at rate of 50 kg ha -1
which was statistically similar with when N applied at rate of 100 kg ha -1 . The lowest
apparent recovery was recorded from N at rate of 150 kg N ha -1 treatment (Table 10).
Generally, the higher N rates increases the apparent recovery of N was decreased. Further
increased N to 100 kg ha -1 apparent recovery was declined or at high application of nutrients
has low nutrient recovery. Such low apparent recovery of higher N might be attributed to the
susceptibility of N to different losses through leaching.
Similarly the application of P fertilizer affected apparent recovery of N. The highest apparent
recovery of N was recorded from P at rate of 105 kg P 2 O 5 ha -1 which was statistically similar
with when P applied at rate of 70 kg P 2 O 5 ha -1 . The lowest apparent recovery was recorded
from P at rate of 35kg kg P 2 O 5 ha -1 treatment (Table 10). Generally, the P rates increases the
apparent recovery of N was consistently increased.
Apparent recovery of P fertilizer was significantly (P<0.01) affected the main effect of
nitrogen (N) and phosphorus (P) as well as the interaction effect of the two factors (Appendix
Table 2).
68

Application of N fertilizer consistently increased the apparent recovery of P. Numerically the
highest apparent recovery of P was recorded from N at rate of 100 kg ha -1 which was
statistically at par with when N applied at rate of 150 kg ha -1 . The lowest apparent recovery
was recorded from N at rate of 50 kg N ha -1 treatment (Table 10). Generally, the higher N
rates increases the apparent recovery of P was increased up to optimum rates.
Similarly the application of P fertilizer the apparent recovery of P was enhanced. Numerically
the highest apparent recovery of P was obtained from P at rate of 35 kg P 2 O 5 ha -1 which was
statistically at par with P at rate of 70 kg P 2 O 5 ha -1 . The lowest apparent recovery was
recorded from P at rate of 105 kg P 2 O 5 ha -1 treatment (Table 10). Generally, the optimum P
rates the apparent recovery of P was increased. This finding is in line with the other crops
Grzebisz et al. (2015) and Salam et al. (2014) which indicate that the level of nutrient
fertilization affects the nutrient availability in soil and at high contents of soil nutrients and
their availability more nutrients might be taken up by plants. The authors stated that
depending upon the nutrient absorption power of the crops and their utilization at the
biochemical levels, crops may vary in the recovery of the applied nutrients.
69

Table 10. The main effect of N and P fertilizers affected on agronomic efficiency,
physiological efficiency, and apparent recovery onion seed production in 2017/2018.
N (kg ha -
Agronomic
Apparent
Physiological
Agronomic
Apparent
Physiological
1 )
efficiency
recovery
efficiency of
efficiency
recovery
efficiency of
of N (kg
(%) of N
N (kg kg -1 )
of P (kg kg -
(%) of P
P (kg kg -1 )
kg -1 )
1 )
0 - - - - - -
50 10.78 a 19.62 a 53.47 a 7.17 b 1.05 b 509.26
100 7.45 b 18.34 a 46.51 ab 10.46 a 2.06 a 554.12
150 4.98 c 14.17 b 37.19 b 11.14 a 1.83 a 488.90
LSD(0.05) 0.76 3.76 13.08 1.32 0.43 Ns
P 2 O 5 (kg
ha -1 )
0 - - - - - -
35 4.92 c 8.32 b 54.32 15.25 a 2.47 a 455.95 b
70 7.21 b 17.69 a 52.82 11.78 b 2.04 a 580.41 a
105 8.24 a 18.09 a 43.09 7.49 c 1.42 b 491.25 ab
LSD(0.05) 0.76 3.76 Ns 1.32 0.43 122.6
CV (%) 15.72 34.64 35.69 18.29 34.96 32.96
LSD 0.05 = least significant difference at 5%, CV (%) = Coefficient of variation, Ns = non
significant. Means in the same columns followed by the same letter(s) are not significantly
different.
4.8. Correlation of N and P Concentrations in Plant Tissues, Agronomic and Yield of
Onion Uptake
The correlation values explain the apparent association of the nutrient parameters with each
other and clearly indicated the magnitude and directions of the association and relationships.
Moreover, N and P uptake of the plant could be the case for N and P concentration increment
in the plant tissues; this positive relationships indicated with positive and highly significant
correlation values of all parameters (Appendix Table 4). This implied that the increased
70

nitrogen and phosphorus concentration of the leaf tissues was the result of increasing uptake
of both N and P and increasing N and P concentration in the plant body. The present result
was in accordance with the findings of Tamrat (2006).
Among the several agronomic and yield components, days to flowering and days to maturity
were negative and significantly correlated with N concentration of leaves and N uptake of
plant positively and highly significant correlated with days to bolting , flowering, maturity,
plant height and flower stalk height. Thus, the result implied that increased N uptake and its
concentration in the plant reduced the time taken for bolting, flowering and maturation. This
agreed with the physiological aspect of the nutrient imposed on plant growth and
development (Marschner, 1995; Tamrat, 2006) (Appendix Table 5).
Umbel size and number of umbel per plant of the onion was positively and highly significant
correlated with nitrogen uptake by plant (r = 0.584**) and (r = 0.998**) respectively. This
similarly implied that the increment of nitrogen concentration in plant caused for the
increment of umbel size and umbel number. N uptake of plant positively and highly
significant correlation was observed number of umbel per plant (r = 0.742**), number of
flower stalk per plant (r = 0.562**), flower stalk diameter (r = 0.584**), number of umbel per
plant (r = 0.998**), seed yield per plant (r = 0.858**) and seed yield per hectare (r = 0.941**)
and P uptake of whole plant positively and significantly correlated with number of seed per
plant (r = 0.782**), seed yield per umbel (r = 0.713**), 1000 seed weight (r = 0.334**), seed
yield per plant (r = 0.633**) and seed yield per hectare (r = 0.691**). For that reason, it is
possible to say that increase of N and P concentration and uptake of the plant parts resulted in
increasing of seed number per umbel and seed yield per hectare. This might be due to the fact
that these two essential elements had positive effect on the physiology of flowering and seed
formation by controlling the photosynthesis (Marschner, 1995; Tamrat, 2006). All N and P
71

concentration in plant tissues and uptake of the plant positively or negatively contribute to
onion seed increment (Appendix Table 5).
4.9. Partial Budget Analysis
A partial budget is a way of calculating the total costs that vary and the net benefits of each
treatment (CIMMYT, 1988).
From this study, the average yield of 16 treatments was obtained. According to CIMMYT
(1988), the average yield was adjusted down wards by 10%. This is for the reason that,
researchers have assumed that using the same treatments the yields from the experimental
plots and farmers’ fields are different, thus average yields should be adjusted downward.
Based on this, the recommended level of 10% was adjusted from all 16 treatments to get the
net yield.
For the different treatment combinations the total costs and net benefits were calculated. As
the rate of N and P fertilizer application increased, each additional kilogram of the fertilizer
had effect on seed yield. To estimate the total costs, mean current prices of Urea and TSP
were collected at the time of planting and market price value of one kg of onion seed was
taken at harvest. The cost for daily labor during the season was 50 birr per day. The field
price of onion seed during the harvesting season was 330 birr kg -1 . Then finally, adjusted
yield was multiplied by field price to obtain gross field benefit of onion. All the variable
costs were subtracted from gross benefit to obtain net benefit.
The result of the economic analysis showed that highest net benefit 488,878.5 ETB ha -1 ,
highest rate of marginal returns 36638% and highest benefit cost ratio 7.66 were obtained
from combined application of 100 N and 70 kg P 2 O 5 ha -1 . It was followed by 50 N and 105
P 2 O 5 kg ha -1 N and P fertilizers which had 429,525 ETB ha -1 net benefit, 27910% rate of
marginal return and 6.74 benefit cost ratio (Table 11 and 12). This indicated that as the total
72

costs that vary increased until certain level, so as the net benefit obtained increased. However,
as the total costs that vary increased over the optimum level, the net benefit obtained reduced
as the result of higher variable costs associated with lower earnings. The cost of onion seed
was exceptionally medium 330 birr per kg from normal market which was 260 birr per kg
when the produce was collected and this was one reason for medium net benefit recorded in
this study.
According to CIMMYT (1988) economic analysis based fertilizer recommendation is not
necessarily based on the treatment with the highest marginal rate of return compared to that of
the next lowest cost, the treatment with the highest net benefit, and nor the treatment with the
highest yield. The identification of a recommendation is based on a change from one
treatment to another if the marginal rate of return of that change is greater than the minimum
rate of return (100%).
73

Table 11. Economic analysis due to the application of N and P fertilizer levels seed yield of
Nafis onion grown at Kulumsa in 2017/2018.
N and P 2 O 5 Average seed Adjusted Gross Field Total cost Net benefit
rate (kg ha -1 ) Yield (kg ha - seed yield Benefit (ETB (ETB ha -1 ) (ETB ha -1 )
1 )
(kg ha -1 ) ha -1 )
0 x 0 952.01 856.81 282747.3 61280 221467.3
0 x 35 1093.55 984.19 324782.7 61843 262939.7
0 x 70 1254.11 1128.69 372467.7 62405 310062.7
0 x 105 1236.09 1112.48 367118.73 62968 304150.73
50 x 0 1053.32 947.99 312836.7 62005 250831.7
50 x 35 1196.56 1076.90 355377 62568 292809
50 x 70 1412.97 1271.67 419651.1 63530 356121.1
50 x 105 1660.67 1494.60 493218 63693 429525
100 x 0 1126.72 1014.05 334636.5 62730 271906.5
100 x 35 1394.38 1254.94 414130.2 63293 350837.2
100 x 70 1861.05 1674.95 552733.5 63855 488878.5
100 x 105 1740.60 1566.54 516958.2 64418 452540.2
150 x 0 1162.68 1046.41 345315.3 64455 280860.3
150 x 35 1591.41 1432.27 472649.1 64018 408631.1
150 x 70 1700.45 1530.41 505035.3 64580 440455.3
150 x 105 1671.67 1504.50 496485 65143 431342
The price of urea and TSP fertilizer was 11.50 and 12.50 ETB kg -1 respectively and selling
price of onion seed was 330 ETB kg -1
74

4.9.1. Dominance analysis, net benefit curve and marginal rate of return
The highest net benefits from the application of inputs for the production of the crop might
not be sufficient for the farmers to accept as good practices. In most cases, farmers prefer the
highest profit with low cost (high income). For this purpose it is necessary to conduct
dominated treatment analysis. A dominated treatment is any treatment that has net benefits
that are less than those of a treatment with lower costs that vary. The Dominance analysis
procedure as detailed in CIMMYT (1988) was used to select potentially profitable treatments
from the range that was tested. The dominant (undominated) treatments were ranked from the
lowest to the highest costs that vary. The dominant analysis showed that the net benefit of 50
kg N ha -1 + 0 P 2 O 5 kg ha -1 , 50 kg N ha -1 + 35 P 2 O 5 kg ha -1 , 100 kg N ha -1 + 0 P 2 O 5 kg ha -1 ,
0 kg N ha -1 + 105 P 2 O 5 kg ha -1 , 150 kg N ha -1 + 35 P 2 O 5 kg ha -1 , 100 kg N ha -1 + 105 P 2 O 5
kg ha -1 , 150 kg N ha -1 + 0 P 2 O 5 kg ha -1 , 150 kg N ha -1 + 70 P 2 O 5 kg ha -1 and 150 kg N ha -1 +
105 P 2 O 5 kg ha -1 treatments were dominated. This indicates that the net benefit was
decreased as the total cost that varies increased beyond non dominated fertilizer treatments
application.
Marginal rate of return (MRR %)
The percentage marginal rate of return (%MRR) between any pair of dominant treatments
denotes the return per unit of investment in fertilizer expressed as a percentage. Passing from
the first treatment that had the lowest costs that vary to the end treatment which had the
highest cost that vary, the marginal rate of return obtained was above the minimum acceptable
marginal rate of return. The best recommendation for treatments not subjected the highest
marginal rate of return, rather based on the minimum acceptable marginal rate of return and
the treatment with the highest net benefit together with an acceptable MRR becomes the
tentative recommendation (CIMMYT, 1988). In this study, 100% was considered as
minimum acceptable rate of return for farmer’s recommendation. For instance for every 1.00
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Birr invested at application of N and P fertilizer, farmers can expect to recover the 1.00 Birr,
and obtain an additional 366.38 Birr ha -1 combined application of 100 N and 70 kg P 2 O 5 ha -1
and also the second alternative recommendation with values of Marginal return ETB 279.10
profit per unit investment for onion seed production was obtained from application of 50 kg N
with 105 P 2 O 5 kg ha -1 (Tables 12). This recommendation is supported by CIMMYT (1988)
which stated that farmers should be willing to change from one treatment to another if the
marginal rate of return of that change is greater than the minimum acceptable rate of return.
Table 12. Dominance analysis and marginal rate of return of the application of N and P
fertilizer rates on onion seed production at Arsi in 2017/2018.
N and P 2 O 5 Total cost Net benefit Dominance Marginal Marginal Benefit
rate (kg ha - (ETB ha -1 ) (ETB ha -1 )
Return rate of cost ratio
1 )
return (%)
0 x 0 61280 221467.3 - - -
0 x 35 61843 262939.7 73.67 7367 4.25
50 x 0 62005 250831.7 Dominated
0 x 70 62405 310062.7 148.08 14808 4.97
50 x 35 62568 292809 Dominated
100 x 0 62730 271906.5 Dominated
0 x 105 62968 304150.7 Dominated
100 x 35 63293 350837.2 143.65 14365 5.54
50 x 70 63430 356121.1 38.57 3857 5.61
50 x 105 63693 429525 279.10 27910 6.74
100 x 70 63855 488878.5 366.38 36638 7.66
150 x 35 64018 408631.1 Dominated
100 x 105 64418 452540.2 Dominated
150 x 0 64455 280860.3 Dominated
150 x 70 64580 440455.3 Dominated
150 x 105 65143 431342 Dominated
76

5. SUMMARY, CONCLUTION AND RECOMMENDATIONS
Onion is one of the most important vegetable crops commercially grown both by large and
small scale farmers in Ethiopia. It is a high value and high income generating vegetable crops
for most farmers in Ethiopia, which is widely produced in small scales and by commercial
growers and considerably important in the daily meal of Ethiopians. Onion is one of the most
important income generation crops both cultivated under rained and irrigation in Arsi Zone
South Eastern Ethiopia.
The enhancement of onion production and productivity can be constrained different growth
factors. Thus, the use of appropriate agronomic management has an undoubted contribution to
increased crop yields. There are a number of constraints that cause low productivity of onion
seed production in Ethiopia. The low yield of onion seed in the country is due to low fertility
of soil, inappropriate fertilizer rate, lack of improved varieties, and poor management
practices. Among these constraints, inappropriate use of mineral fertilizer was one of the most
important management factors in Arsi Zone.
A field experiment was conducted under irrigation condition during the off- season of
October 2017 to March 2018 at Kulumsa, South-Easter Ethiopia. The treatments were
combinations of four levels of N (0, 50, 100, and 150 kg ha -1 ) from urea (46-0-0) and four
levels of P 2 O 5 (0, 35, 70, and 105 kg ha -1 ) from TSP (0-46-0). The treatment combinations
were arranged factorially in randomized complete block design (RCBD) with three
replications.
The results of the study revealed that most of the onion seed parameters considered was
significantly affected by the N and P treatments. Days to bolting, flowering and maturity were
significantly affected by level of N and P fertilizers. Early bolting, flowering and maturity
days were recorded with the application of fertilizer with 0 kg N with 70 and105 kg P 2 O 5 ha -1 .
77

On the other hand, delay in days to bolting, flowering and maturity was recorded from control
and at highest N fertilizer rates. Other growth parameters such as plant height were also
significantly increased with application of N and P fertilizers; the highest results were
obtained from fertilizer rate of 100 kg N with 70 kg P 2 O 5 ha -1 . In contrast, growth parameters
as well as yield and yield components were lowest at the control treatments. Among the yield
and yield components, the highest and significantly different onion seed yield per umbel (3.56
g), seed yield per plant (10.82 g) and seed yield per hectare (1858.82 kg ha -1 ) were obtained
from plots that received the combination of N and P fertilizer rate of 100 kg N with 70 kg
P 2 O 5 ha -1 . It was also noted that, among the yield components, increase in number of flowers
per umbel, number of flower stalk per plant, flower stalk and umbel diameter, number and
weight of seed per umbel were responsible for the observed yield advantage. In general,
combined application of 100 kg N with 70 kg P 2 O 5 ha -1 fertilizers improves onion seed yield
as compared to control treatments of no fertilizer applied. Seed quality parameters
significantly affected by N and P fertilizers. The highest germination percentage was recorded
from application of each of 100 kg N ha -1 and 105 kg P 2 O 5 ha -1 as the main factor,
respectively. Thousand seed weight was affected only by P fertilizer that 70 kg P 2 O 5 ha -1
resulted in maximum 1000 seed weight. The available P was increased after harvest due to the
application of N and P fertilizer at the rates of 100 or 150 kg N ha -1 and 70 or 105 kg P 2 O 5 ha -
1 .
The nutrient concentrations and uptakes were linearly increased in response to the application
of N and P fertilizers rates whereas; nutrient use efficiency was decreased with increasing N
and P fertilizers after optimum rates. The higher physiological efficiency of N (53.47 kg kg -1 )
and P (580.41 kg kg -1 ) and the highest apparent recovery of N (19.62%) and P (2.47%) was
recorded from application of 50 kg N ha -1 and P at 70 kg P 2 O 5 ha -1 and the highest agronomic
efficiency N (10.78 kg kg -1 ) and P (15.25 kg kg -1 ) were recorded from N rate of 50 kg N ha -1
78

and P at 35 kg P 2 O 5 ha -1 respectively. The fact that all the crop yield parameters being linearly
increased with rising N and P fertilizer rates up to optimum and declined for further increase.
Correlation coefficient values indicated that seed yield per hectare was directly and highly
significantly related with yield and yield components. The relationship of the uptake of N and
P were significantly and very strongly correlated (P< 0.01) with seed yield per plant. This
indicates that improvement of total seed yield per hectare was through high nutrient uptake.
According to partial budget analysis the highest net benefit (488,878.5 Birr ha -1 ) of marginal
returns (36638) and highest benefit cost ratio (7.66) were obtained from the combination of
100 kg N ha -1 and 70 kg P 2 O 5 ha -1 .
As conclusions, N application resulted in pronounced effect on vegetative characters of onion
than the phosphorus effect in the combined application. As nitrogen rates increased, onion
seed maturity delayed. The moderate amount of the experimental soil may compromise the
applied P fertilizer on the vegetative characters owing to its little inherent contributions for
vegetative growth. The seed yield increased with the increasing combinations or rate of
nitrogen and phosphorus fertilizers. The seed yield obtained by the interaction effect greater
the two nutrients in the seed yield per hectare.
Generally, nitrogen and phosphorus fertilizer application would be preferred for onion seed
production. The application of nitrogen at 100 kg N ha -1 and phosphorus at 70 kg P 2 O 5 ha -1
appeared to be a promising combination which gave highest benefit cost ratio (marginal rate
of return) which could be recommended for high onion seed yield with the required quality in
the study area. However, in order to give conclusive recommendation for the study area,
similar field and economic feasibility studies need to be carried out at least for one more
cropping season.
79

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7. APPENDICES
Appendix Table 1. Mean square values for yield and other agronomic traits of onion as affected by main and interaction effects of nitrogen and
phosphorus fertilization in 2017/2018
Agronomic data
Mean square
N P NXP Error
R 2
Root
MSE
Days to bolting 36.75** 8.14** 5.55** 1.08 0.855 1.04
Days to flowering 181.89** 6.28** 4.75** 1.51 0.932 1.23
Days to maturity 106.80** 35.14* 7.78 ns 11.66 0.741 3.06
Plant height 511.67** 13.01 ns 38.33* 13.75 0.838 3.56
Flower stalk height 251.65** 20.88 ns 67.25 ns 31.01 0.724 4.97
Flower stalk diameter 0.77* 0.17 ns 0.19* 0.08 0.756 0.28
Umbel diameter 2.24** 1.21** 0.61** 0.14 0.802 0.38
No of flower stalk per plant 42.08** 6.59* 6.71* 2.24 0.757 1.49
No of flower per umbel 59352.37** 30598.58* 3539.29 ns 5069.85 0.691 71.20
No of umbel per plant 84.82** 24.56** 2.44* 0.89 0.929 0.95
Stand count at harvest 20.38 ns 25.21 ns 15.18 ns 45.16 0.99 6.72
No of seed per umbel 164996.9** 328502.1** 17147.5 ns 10137.3 0.844 100.68
Weight of seed yield/ umbel 1.89** 3.49** 0.34** 0.15 0.817 0.39
Weight seed yield per plant 9.09** 17.74** 1.25** 0.49 0.861 0.70
Seed yield per ha 44.73** 83.74** 4.057** 1.33 0.914 115.45
1000 seed weight 0.10ns 0.35* 0.11 ns 0.07 0.683 0.26
% germination at harvest 5.39* 61.39** 1.74 ns 1.02 0.877 1.01
91

Appendix Table 2. Mean estimation of P and N nutrient in the soil and onion plant tissue in response to nitrogen and phosphorus fertilization
Mean square R 2 Root
Nutrient parameters N P NXP Error
MSE
Total nitrogen of soil 0.0011** 0.00024 ns 0.00063** 0.00011 0.753 0.01
Available phos.of soil 63.92** 69.08** 23.49** 0.652 0.889 0.81
N conc. in leaves 0.035** 0.0062** 0.011** 0.00063 0.923 0.025
N conc. in seeds 0.055** 0.033** 0.029** 0.0019 0.902 0.044
N uptake of leaves 516.63** 358.74** 32.25 ns 28.096 0.781 5.301
N uptake of seed 0.143** 0.198** 0.014** 0.0017 0.957 0.041
N uptake of whole plant 533.36** 374.32** 28.07 ns 28.066 0.786 5.297
P conc. in leaves 0.00021** 0.000198** 0.000017 ns 0.000018 0.794 0.0035
P conc. in seeds 0.0024** 0.00099** 0.0001 ns 0.000055 0.872 0.0074
P uptake of leaves 1.965** 2.032** 0.175 ns 0.1063 0.814 0.336
P uptake of seeds 0.0047** 0.0051** 0.00025* 0.00009 0.922 0.0095
P uptake of whole plant 2.155** 2.235** 0.174 ns 0.1065 0.825 0.326
Agronomic efficiency(N) 247.26** 70.40** 17.99** 0.83 0.982 0.912
Physiological efficiency(N) 682.57* 2094.53 ns 567.42* 246.22 0.678 15.691
Apparent recovery(N) 970.68** 379.10** 115.90** 20.38 0.89 4.51
Agronomic efficiency(P) 80.23** 517.79** 27.27** 2.49 0.967 0.912
Physiological efficiency(P) 253.43 ns 224332.05** 17566.11 ns 21622.09 0.72 147.05
Apparent recovery(P) 3.51** 13.94** 0.97** 0.27 0.89 0.52
92

Appendix Table 3. Pearson Correlation among agronomic and yield components of onion crops in 2017/2018.
DB DF Ph MD FSH NFU NFSP FSD UD NUP NSU SYU TSW WSPL Syha
DB 0.75** 0.43** 0.56** 0.27 0.29* 0.31* 0.18 0.19 0.45** -0.12 0.01 -0.19 -0.03 -0.07
DF 0.67** 0.70** 0.48** 0.43** 0.49** 0.37** 0.41** 0.65** -0.27 -0.17 -0.22 -0.19 -0.26
Ph 0.38** 0.82** 0.49** 0.38** 0.49** 0.56** 0.58** -0.15 -0.13 -0.24 -0.16 -0.22
MD 0.15 0.233 0.29* 0.05 0.2 0.31* -0.17 -0.14 -0.08 -0.15 -0.17
FSH 0.45** 0.38** 0.5** 0.45** 0.48** -0.17 -0.19 -0.15 -0.2 -0.29
NFU 0.35* 0.41** 0.42** 0.74** 0.24** 0.19** -0.13 0.23** 0.33**
NFSP 0.45** 0.59** 0.56** 0.79 0.75 0.5 0.43* 0.56**
FSD 0.54** 0.56** 0.86* 0.68* 0.79* 0.69* 0.78*
UD 0.58** 0.5* 0.32 0.15* 0.43* 0.77**
NUP 0.25 0.21 -0.64 0.56** 0.62**
NSU 0.92** 0.26 0.70** 0.77**
SYU 0.22 0.74** 0.77**
TSW 0.31* 0.39**
WSPL 0.94**
Syha 1
* & ** Significant at 5% and 1% probability levels, respectively. The decimal numbers without any asterics are non significant (P>0.05), DBdays
to bolting, DF=days to flowering, DM=days to maturity, FSH=flower stalk height, FSD=flower stalk diameter, UD=umbel diameter,
NUP=number of umbel per plant, NSU=number of seed per umbel, WSU =weight of seed per umbel, TSW=1000 seed weight, SYP-seed yield
per plant, SY ha=seed yield per hectare.
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Appendix Table 4. Pearson Correlation among N and P concentrations in soils and plant tissues and uptake parameters in 2017/2018.
TN AVP NCL NCS NUL NUS NUP PCL PCS PUL PUS PUP
TN 0.428** 0.328** 0.552** 0.412** 0.476** 0.414** 0.497** 0.457** 0.457** 0.429** 0.463**
AVP 0.617** 0.543** 0.778** 0.839** 0.782** 0.716** 0.711** 0.734** 0.858** 0.747**
NCL 0.527** 0.654** 0.613** 0.656** 0.497** 0.539** 0.422** 0.574** 0.433**
NCS 0.603** 0.713** 0.608** 0.599** 0.483** 0.574** 0.463** 0.576**
NUL 0.744** 0.999** 0.722** 0.733** 0.899** 0.745** 0.902**
NUS 0.752** 0.754** 0.671** 0.726** 0.915** 0.742**
NUP 0.725** 0.735** 0.901** 0.751** 0.904**
PCL 0.696** 0.897** 0.749** 0.901**
PCS 0.723** 0.826** 0.735**
PUL 0.739** 0.999**
PUS 0.759**
PUP 1
** Significant at 1% probability levels. The decimal numbers without any asterics are non-significant (P>0.05), NUL=nitrogen uptake of leaves,
NUS=nitrogen uptake of seed, NUP=nitrogen uptake of plant, PUL=phosphorus uptake of leaves, PUS=phosphorus uptake of seed and PUP=
phosphorus uptake of plant, TN= total nitrogen and AVP= available phosphorus.
94

Appendix Table 5. Correlation coefficients (r) among selected and related characters of N and P uptake and their concentration in the plant
tissues with agronomic and yield components in 2017/2018.
DB DF DM PH FSH NFU NFSP FSD UD NUP NSU SYU TSW SYPL SY ha
NCL -0.277 -0.41** -0.39** -0.295* -0.162 -0.32* -0.156 -0.215 -0.214 -0.47** 0.512** 0.467** 0.246 0.523** 0.547**
NCS -0.197 -0.230 -0.192 -0.266 -0.125 -0.50** 0.129 -0.073 -0.197 -0.316* 0.474** 0.359** 0.557** 0.363** 0.483**
NUL -0.283 -0.252 -0.259 -0.219 -0.182 -0.32** -0.03 -0.110 -0.077 -0.262 0.731** 0.644** 0.348 0.641** 0.666**
NUS -0.131 -0.295* -0.205* -0.302 -0.291* -0.39** 0.17 -0.082 -0.118 -0.350* 0.777** 0.740 0.490** 0.257* 0.422**
NUP 0.452** 0.650** 0.313** 0.583** 0.480** 0.742** 0.563** 0.563** 0.584** 0.998** 0.249** 0.211** -0.64 0.858** 0.941**
PCL -0.143 -0.194 -0.178 -0.203 -0.214 -0.38** 0.106 -0.114 0.070 -0.236 0.769** 0.722** 0.309* 0.637** 0.718**
PCS -0.101 -0.147 -0.163 -0.085 -0.089 -0.324* -0.089 0.001 -0.108 -0.238 0.670** 0.664** 0.201 0.581** 0.633**
PUL -0.194 -0.152 -0.168 -0.171 -0.192 -0.314* 0.100 -0.065 0.065 -0.157 0.772** 0.701** 0.331* 0.614** 0.671**
PUS -0.091 -0.247 -0.184 -0.203 -0.249 -0.323* -0.066 -0.051 -0.079 -0.310* 0.796** 0.806** 0.326* 0.897** 0.947**
PUP -0.191 -0.158 -0.171 -0.174 -0.197 -0.318* 0.094 -0.065 0.059 -0.165 0.782** 0.713** 0.334* 0.633** 0.691**
* & ** Significant at 5% and 1% probability levels, respectively. The decimal numbers without any asterics are non-significant (P>0.05)
DB=days to bolting, DF=days to flowering, PH=plant height, FSD=flower stalk diameter, NFSP= number of flower stalk per plant, UD=umbel
diameter, NUP-number of umbel per plant.NUL=nitrogen uptake of leaves, NUS=nitrogen uptake of seed, NUP=nitrogen uptake of plant,
PUL=phosphorus uptake of leaves, PUS=phosphorus uptake of seed and PUP= phosphorus uptake of whole plant.
95

Appendix Table 6. Main effect of nitrogen and phosphorus on plant growth and seed characters of Nafis onion Cultivar in 2017/2018
Treatment Number of days to Plant
N (kg ha -1) bolting 50%
flowering
height
(cm)
Flower
stalk
Diameter
(cm)
No of
flower
stalk
per
plant
Umbel
diameter
(cm)
No of umbel per
Seed
Weight
per
umbel
(g)
Seed
Weight
per
plant
(g)
Seed
yield
kg ha -1
Total N
0 50.58 d 85.92 d 83.10 b 2.08 b 8.64 b 4.80 c 7.27 c 425.97 c 2.36 b 7.77 c 1127 c 0.158 b 6.44 d
50 52.25 c 90.92 c 95.07 a 2.18 b 9.15 b 5.35 b 8.82 b 668.18 b 2.67 b 8.51 b 1331 b 0.165 b 7.29 c
100 53.25 b 92.75 b 97.39 a 2.62 a 11.66 a 5.54 ab 12.14 a 879.72 a 3.17 a 9.43 a 1530 a 0.179 a 8.38 b
150 54.75 a 95.08 a 95.56 a 2.48 a 12.47 a 5.83 a 12.83 a 947.48 a 3.17 a 9.66 a 1532 a 0.174 a 9.51 a
P 2 O 5 (kg
ha -1 )
0 53.67 a 91.75 a 91.23 2.19 10.08 b 4.09 c 8.81 b 422.15 c 2.11 c 7.29 c 1032 c 0.163 a 6.27 c
35 53.08 ab 91.83 a 91.38 2.31 9.79 b 5.13 b 9.27 b 646.79 b 2.83 b 8.46 b 1319 b 0.169 a 7.24 b
70 51.83 c 90.58 b 93.15 2.47 10.57 ab 5.58 a 11.42 a 788.09 a 3.05 b 9.79 a 1562 a 0.174 a 8.97 a
105 52.25 bc 90.50 b 93.36 2.38 11.48 a 5.71 a 11.57 a 864.3 a 3.38 a 9.82 a 1607 a 0.169 a 9.14 a
LSD(0.05) 0.87 1.023 NS NS 1.25 0.32 0.79 104.83 0.32 0.59 96.25 0.086 0.67
CV (%) 1.98 1.35 3.83 12.42 14.28 7.03 9.22 14.28 13.59 7.97 8.37 6.13 10.22
plant
plot
(%)
Available
P(ppm)
LSD 0.05 = least significant difference at 5%, CV (%) = Coefficient of variation, Ns= non significant. Means in columns with the same letter(s) in
each treatment are not significantly different.
96

Appendix Table 7. Soil physical and chemical properties of the surface soil (0-30 cm depth)
of the experimental site before planting in 2017/2018
Characteristic unit Quantity
Sand % 6.25
Silt % 30
Clay % 63.75
Textural Class - Clay
pH(1:2.5 H 2 O) - 6.3
Total Nitrogen % 0.18
Organic Matter % 5.05
Organic Carbon % 2.93
Available Phosphorus ppm 5.42
97

Appendix Table 8.
Weather conditions in 2016, 2017 and 2018 main cropping season at
Kulumsa in 2017/2018.
2016 2017 2018 2016 2017 2018 2016 2017 2018
Month Rainfall
(mm)
Rainfall
(mm)
Rainfall
(mm)
Tmin
( 0 C)
Tmin
( 0 C)
Tmin
( 0 C)
Tmax
( 0 C)
Tmax
( 0 C)
Tmax
( 0 C)
January 20.9 0.0 0.0 11.9 9.2 9.3 24.7 24.1 23.6
February 1.9 29.1 43.9 11.3 10.7 10.4 26.4 24.6 24.6
March 38.2 87.2 30.2 14.2 11.8 12.5 29.2 27.2 25.2
April 250.1 25.3 165.1 13.9 13.5 12.8 24.5 27.1 24.1
May 59.1 52.7 53.6 12.8 13.2 14.1 23.9 23.9 24.7
June 118.9 64.2 127.3 12.0 12.7 12.8 23.5 24.7 22.7
July 136.0 164.6 12.8 13.0 22.2 22.5
August 125.0 109.1 12.6 12.7 22.0 21.9
September 96.9 131.8 11.8 12.2 22.6 21.4
October 19.2 12.6 12.1 12.6 24.2 23.6
November 14.2 0.0 11.2 11.0 23.5 23.4
December 0.0 0.0 10.4 8.1 22.8 22.5
Total/mean 880.4 676.6 420.1 12.25 11.73 11.98 24.13 23.91 24.15
Source: KARC Metrology Station (2017)
98

BIOGRAPHICAL SKETCH
The author, Demis Fikre Limeneh was born on 26 Sep, 1989 G.C in Arsi Zone of Oromia
Regional State. He attended his primary education at Kereyu and Gedjeda Primary School
and Secondary and preparatory school at Ticho. Then he joined Ambo University, College of
Agriculture, and Veterinary Science in October 25, 2011 to pursue a study leading to the
degree of Bachelor of Science in Horticulture and graduated with the degree of Bachelor of
Science in Horticulture in July 03, 2013. After graduation, he served at Ethiopian Institute of
Agricultural Research (EIAR) as a Horticulturist. In 2016/2017, he joined Postgraduate
Program of Hawasa University to pursue a study leading to the degree of Master of Science in
Horticulture.
99