Grain Legumes and Green Manures for Soil Fertility in ... - cimmyt

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organic and inorganic (mineral) fertilizers, and crop removal without the return of nutrients. Soil Fertility Status of Malawi Soils Soil fertility is defined as the ability of the soil to supply the nutrients needed by plants (Ahn, 1993). According to Young and Brown (1962; 1965), nitrogen is the most limiting nutrient element in Malawian soils. Sulphur deficiencies are prevalent in some areas. In most upland areas, the soils are highly leached and as such, they are dominated by iron and aluminium oxides that fix phosphorus into forms that-are unavailable for plant uptake. Phosphorus studies by Mughogho (1975) on some soils in Malawi indicated that soils in Mulanje, in the southern region of Malawi, fix a lot of phosphorus. This is one of the high rainfall areas that receives 1200-1800 mm of rain annually. Soil Fertility Research Reviews in Malawi Mughogho (1989) conducted a review of soil fertility research in Malawi. The overall objective of that work was to document existing information on soil fertility research from Malawi and other appropriate sources, to be used as a planning tool and database for proposed soil fertility ' studies. Findings from that study indicated tQat 'in, addition to low soil nitrogen, most soils have large quantities of sesquioxides that fix phosphorus into unavailable forms, and sulphur is deficient in some areas. Mughogho (1989) further recommended the need for a detailed study on the characterization of soils in Malawi to build upon the work by Brown and Young (1962; 1965). The potential of sources of phosphate rock, to be used on acid soils needs to be explored. A review report by Gilbert and Kumwenda (2001) highlighted some of the best-bet legumes for smallholder maize-based systems. For Instance, Mucuna pruriens was described as a promising green manure. Successful grain legume-maize rotations and intercrops of pigeonpea or Tephrosia with maize were observed. The following sections look in more detail at green manures, crop rotations (especially with grain legumes) and agroforestry interventions to raise soil fertility and maize productivity in Malawi. Green Manures Follet et al. (1981) defined a green manure crop as one that is grown and incorporated into the soil to add organic matter and N and subsequently improve crop yields. In Malawi, most farmers have used weeds as green man~.ue materials. These are 96 incorporated at the time of ridging, weeding or banding. The benefits from green manures include reduction of nutrient.loss through leaching, the accumulation and maintenance of soil N, and improvement of soil structure. Other species like Mucuna pruriens help to reduce weeds (CIMMYT, 1998), thereby minimizing competition for soil nutrients and water. The success of a green manure for soil fertility improvement depends on its quality (CN ratio), quantity of the material, and management (especially the timing and means of biomass incorporation). Proper timing allows nutrient release in synchrony with crop uptake. High biomass production can be attained if all essential soil nutrient ekments are available. For instance, Giller and Wilson (1991) noted that phosphate fertilizer applications are necessary to support the luxurious growth of the green manure and hence its potential as an organic source of fertilizer. There are some leguminous species with higher quality biomass, and good ability to fix nitrogen biologically in Malawi. Some of these species include Tephrosia vogelii, Sunnhemp (Crotalaria juncea), Tithonia diversifolia and velvet bean (Mucuna pruriens). Benefits from the use of Mucuna pruriens, Tephrosia vogelii, sunnhemp, and bulrush millet have been reported (Lungu, 1973; Sakal a et al., 2001; and Mwalwanda, 2002). However, Lungu pointed out that the one year lost to a sole crop green manure or improved fallow is a cost to a farmer and therefore this may reduce farmer interest and adoption. The feasibility of improving soil fertility and maize yield through intercropping or rotation of maize with legumes was investigated at Chitedze Research Station in central Malawi (Kumwenda et al. 2001) from the 1995/96 to 1998/99 crop seasons. The treatments were as indicated in Table 2. The results in Figure 1 illustrate that intercrops of maize with pigeonpea and sunnhemp gave higher yields than the maize/Mucuna system. Maize/ Table 2. Treatments from maize x green manure intercrop and rotation experiments in Malawi from the 1994/95 to 1998/99 crop seasons 1994/95 1995/96 1996/97 1997/98 1998/99 Intercrop Maize/PP Sarpe Same Same Same Maize/ Same Same Same Same Mucuna Maize/ Same Same Same Same sunnhemp Sale Pigeon pea Sale maize Sale maize Sale maize Sale maize Sunnhemp Sale maize Sale maize Sale maize Sale maize Mucuna Sole maize Sole maize Sole maize Sole maize Maize Sole maize Sole maize Sole maize Sale maize PP - Pigeon pea Same - same treatment as in 1994/95 crop season was grown Grain Legumes and Green Manures for Soil Fertility in Southern Africa
7000 6000 ';' €.. 5000 .~MzSole ::!. 4000 o MlIPP ~ ;;: 3000 mMlISunhemp .~ ~ 2000 1000 0 I nte(crop Rotation Cropping s~tem III MlIMucuna Figure 1. Maize grain yield (kg hal) from different cropping systems, across four crop seasons in Malawi, 1995/96·1998/99. Source: Kumwenda et aI., 2001 Mucuna mtercroppmg yielded the least due to competition for growth resources. Rotation trials gave higher maize yields than the intercroppmg system due to larger biomass production from the legumes. However, an economic analysis indicated that continuous maize had higher net benefits than the legume-maize rotation. Similar studies on ~igeonpea by Sakala (1998) have indicated that a farmer is better off opting for maize/ pigeon intercroppmg than for a pigeonpea-maize rotation or the maize-maize cropping system. Other studies have looked at the time of incorporation of the green manures as a factor that influences their potential as soil fertility enhancers. Kumwenda et al. (2001) carried out experiments where biomass was mcorporated at either the time of maximum flowering, at pod initiation (early incorporation) or at harvest (late incorporation). Three species, M. pruriens, C. juncea and T. vogelii were used, along with maize. Higher maize gram yields were obtained from early-incorporated residues than with late. mcorpora.tion (Table 3) . This was attributed to high CN ratios and high lignin contents in the late incorporated residues. However, work by Sakala et al. (2001) revealed that with late incorporation, lower yields are obtained in the first year Table 3. Maize grain yield (kg hal) as influenced by legume crop residues and time of incorporation at five sites in Malawi, 1996/97 cro season legume crop/Maize Time of incorporation Mean yield (kg ha") M. pruriens Early 3392 late 2223 C. juncea Early 3218 late 2692 I T. vogelii Early 2845 late 1483 I Maize·maize 397 Source: Kumwenda et ai., 2001 only but m the subsequent years farmers realize higher yields, which was attributed to the build-up of nutrients. It was therefore recommended that farmers who are constrained for labour would still chose late incorporation and realize a longer stream of higher maize yields. A three-year study was carried out m Southern Malawi by Kamanga et al. (1999) to examme the feasibility of inter-plantmg nitrogen fixmg perennial legumes into maize fields as a way to periodically add green manures to maize. The treatments were Sesbania sesban, Tephrosia vogelii, Pigeonpea (Cajanus ca;an) and maize. The legumes were relay mtercropped with maize at first w eedmg. It was shown that the application of 48 kg N ha- 1 combined with residue incorporation increased maize yields by 62 71 %. Higher maize yields were obtamed from the inter-planting of S. sesban (2.9 t ha- 1 ) and T. vogelii (2.6 t ha- 1 ) than from pigeonpea (2 .1 t ha- 1 ) and maize stover (2.0 t ha- I ). Crop Rotation Crop rotation refers to the repetitive cultivation of an ordered succession of crops on the same land (Mloza-Banda, 1994). The aim is to maintam and improve soil fertility, includmg both its physical and chemical characteristics. It also ensures that the carryover of pests and diseases from one season to another is minimized. The benefits from crop rotations involvmg grain legumes (groundnut, bambara nut and soya bean) over a continuous maize-maize cropping system have been reported in several studies in Malawi (Brown, 1958; Lungu, 1973 and MacColl, 1989; Kumwenda, 1996; and Mhango, 2002). This has been attributed to improved soil fertility through biological nitrogen fixation (BNF) and crop residue incorporation. However, grain legume-maize rotations are not efficient because of the inadequate biomass they prod uce and the small amounts of N retained in crop residues to meet the N requirements of the subsequent maize crop. Giller Jnd Wilson (199\) pointed out that most of the N fixed by grain legumes is exported away from the field due to high nitrogen grain harvest· indices. Other studies have looked into the inclusion of pastures in crop rotations to enhance maize prod uction. Maceoll ( 1990) reported on long term trials whose aim was to determine the contribution to maize yield from a previous pasture legume crop. The treatments were two rates of N (0 and 80 kg N ha- I ) from CAN fertilizer; maize, pure silver leaf, pure stylo, silver leaf/ rhodes grass, and stylo/rhodes grass. Pastures were grown from 1981 to 1984, and then the plots Grain legumes and Green Manures for Soil Fertility in Southern Africa 97
Page 2 and 3:
Grain Legumes and Green Manures for
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Acknowledgments • The Leopard Roc
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Evall!ating mucuna green manure tec
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INTRODUCTION AND CONFERENCE OBJECTI
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Table 1. Paradigm shifts underlying
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100 90 80 - - 0 - - Uptake by ihe m
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- 6 ~ 9 8 7 0- 5 CḎ ns 4 0::: 3
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Table 3. Millet grain and total dry
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Dvorak KA 1996. Adoption potential
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LEGUMES FOR SOIL FERTILITY IN SOUTH
Page 25 and 26:
to the system in such a way that th
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Muetzelfeldt, R.1. 1995. A framewor
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ing capacity. Legumes offer other b
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people/km2), land holdings are smal
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ments. It would help researchers to
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Own livestock Gununo farmers for th
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Questions and Answers ~ey Papers To
Page 42 and 43:
Historical Perspective on Soyabean
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ganic amendment for resource-poor f
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MPhil. Thesis. University of Zimbab
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deal of research work has been bias
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1600 '7 ns 1400 ~ 1200 Cl ~ 1000 "C
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Arbuscular mycorrhizal fungi (AMF)
Page 54 and 55: Boswell EP, Koide RT, Shumway DL, A
Page 56 and 57: Materials and Methods The trial was
Page 58 and 59: 0.9 0.8 ~ 0.7 Rec '-' 0.6 Vl ::9 0.
Page 60 and 61: Series no 5. Soil Science SOciety o
Page 62 and 63: Materials and Methods Persistence o
Page 64 and 65: content resulted in increased rhizo
Page 66 and 67: (Mugwiia and Murwira, 1997). Howeve
Page 68 and 69: Table 2. Average maize yield estima
Page 70 and 71: implied that most fanners prefer to
Page 73 and 74: ] Questions and Answers Rhizobium,
Page 75 and 76: ADDING A NEW DIMENSION TO THE IMPRO
Page 77 and 78: Materials and Methods The study use
Page 79 and 80: a) Chikwaka b) Chinyika !21 C. absu
Page 81 and 82: Table 3. N, P and Kconcentrations (
Page 83 and 84: Abstract SCREENING OF SHORT DURATIO
Page 85 and 86: Table 2. Characteristics of short d
Page 87 and 88: RISK DIVERSIFICATION OPPORTUNITIES
Page 89 and 90: management technologies with differ
Page 91 and 92: Table 3. Expected annual returns (Z
Page 93: Table 6. Risk diversification indic
Page 96 and 97: een renewed interest in green manur
Page 98 and 99: unfertilised maize crop of over 200
Page 101 and 102: Questions and Answers Screening of
Page 103: GREEN MANURE AND FOOD LEGUMES RESEA
Page 107 and 108: Table 5. Maize grain yield (kg ha")
Page 109: Phiri, A.D.K. 1999. Effects of Sesb
Page 112 and 113: amount of roots with sl:nnhemp. It
Page 114 and 115: It was proved that a mixed farming
Page 116 and 117: Table 3. Above·ground biomass (t/h
Page 118 and 119: and horticulture in Zimbabwe: Case
Page 121 and 122: GRAIN LEGUMES AND GREEN MANURES IN
Page 123 and 124: Results Table 1. Adaptation of gree
Page 125 and 126: Four rates of fertilizer N were app
Page 127 and 128: THE ROLE OF COWPEA (VIGNA UNGUICULA
Page 129 and 130: Table 1. Non-legume cropping patter
Page 131 and 132: Table 9. Common pests on cowpeas as
Page 133 and 134: few of the farmers interviewed acqu
Page 135: Murwira, H.K., M.J. Swift and P.G.H
Page 138 and 139: Materials and Methods On farm exper
Page 140 and 141: 18000 1600) 14000 a) Zambia 12000 m
Page 143 and 144: EFFECT OF DIFFERENT GREEN MANURE LE
Page 145 and 146: .. ~ Table 2. The effect of time o
Page 147: Chivinge, O.A., E. Kasembe, and I.K
Page 150 and 151: times with regionally specific adap
Page 152 and 153: ter content at 180 cm was still wel
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to amount of biomass, quality of bi
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with the natural fallow, which did
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and K to maize as an equivalent amo
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forts to understand the mechanisms
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gen recovery rates in relation to p
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The first steps to improve soil fer
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Questions and Answers .Identificat
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MUCUNA - MAIZE ROTATIONS AND SHORT
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Table 3. Percent nitrogen (% N) con
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~e decomposition of legume residues
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Table 3. Effect of forage legumes o
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available nutrients and vice versa,
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Conclusion and Recommendation Mucun
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Specific objectives were to: • Te
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'"~ v '" ~ ~ 1400000 1200000 100000
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EFFECT OF SURFACE APPLICATION AND I
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it 4 a···· · ... - :.!! e.....
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PERFORMANCE OF GREEN MANURES AND GR
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Mungwi soil, cowpea and soyabean pr
Page 198 and 199:
Among BNF systems, symbiotic system
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3500 .f"'3000 ca ,c2500 CI "" - 200
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above-ground biomass was not transl
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3000 "0 ]i >. ,5 ~ C> 800 600 400 2
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Most interventions involving green
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~ ~~----.-~r-~-------------r~~ Aoo
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stover N, followed by after pigeon
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tems in Malawi and Zimbabwe. Procee
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1965). The tailings and AgLi were a
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The significant soybean yield could
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twice the yield is necessary. We ha
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Table 1. Maize and Grain Legumes Pr
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Recommendations and Conclusion In v
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performance of private sector compa
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the investment costs incurred. The
Page 228 and 229:
Results and Planning Workshop. Soil
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A SOCIO-ECONOMIC ANALYSIS OF LEGUME
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Table 1. Gross margins from the dif
Page 235 and 236:
Abstract LINKING TECHNOLOGY DEVELOP
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3. If households are linked to prod
Page 239 and 240:
Table 9. Average Table 8. Pigeonpea
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ance of sorghum-pigeonpea intercrop
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Mligo, J.K., 1995. Pigeonpea breedi
Page 246 and 247:
To Charles Nhemachena, et al. Q: 1)
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• Assessment of the potential ben
Page 250 and 251:
few studies characterized the house
Page 252 and 253:
• Conduct more research to measur
Page 254:
Socio-Economics, Policy and Technol
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