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

The first steps to improve soil fertility management
based on legumes has taken place through crop rotation
studies with green manure cover crops including
improved fallow (pigeon'p~a, lab-lab and
cowpea) in Nhacoongo Research Station in lnhambane
Province. The rotation system consists of three
main components, namely pigeon pealcowpea
intercrop (hot season), sole maize (cool season) and
groundnutlcassava intercrop (in the following hot
season.
Methodology
Site Description
Inharrime district, located in the south of Inham­
bane Province, lies from latitude 24°10'30" and
24°37'30" South and longitude 34°30'00" - 35°25'00"
East. It has 76,518 inhabitants relaying on subsis­
tence agriculture.
According to the Thornthwaite-modified classifica­
tion (Reddy, 1986), the climate is wet semi-arid
(Table 1). The rainfall is irregular and erratic due to
occurrence of low-pressure centers. There are two
growing seasons (Table 1).
Inharrime is located along the coastal zone. Most of
the soils are sandy loams except the low plateau,
then the middle and the high plateau. The dominant
soils are arenosols (Table I), used for most of the
crop production. Locally there are fluvisols and
soils with hydromorphic properties.
Material and Methods
The experiments were planted in lnharrime district
(after having carried out previous studies at the re­
search station of Nhacoongo) on five smallhold
farmers in the areas surrounding the research sta­
tion. In consultation with local farmers, the criteria
were based on farmer's availability and int~rest,
particularly the ones cultivating the legumes. At the
trial s,ites, soil samples taken for chemical character­
istics and texture determination showed nutrient
deficiencies (Table 2).
Table 1. Experimental site details
location
Inharrime district
Altitude
43 mabove sea
level
Average 'annual rainfall 800·1000 mm
Annual mean temperature 23·26°C
Potential evapotranspiration 1275mm
Growth period
130·139 days
Main crop season
September·March
~ Crop season April to September
Dominant soils
Sandy soils
Research station soils
Sandy soils
Farmers fields soils
Sandy soils
Table 2. Soil analysis results of sandy soils from a representative
sample of the smallholders farmer'S field areas
Farm Ca Mg K Na Bas8$ pH in P % %
H2O Olsen Organic Total
Matter ' N
0.40 0.18 0.08 0.00 0.70 6.1 1.49 0.6 0.06
2 1.11 0.25 0.08 0.06 1.50 5.8 1.08 0.5 0.09
3 0.79 0.30 0.16 0.04 1.30 5.9 1.76 0.6 0.07
4 0.69 0.22 0.12 0.04 1.10 6.0 1.35 0.5 0.07
5 0.10 0.34 0.02 0.02 0.50 ' 5,5 1.22 0.5 0.07
The experiment was arranged in a randomized
complete block design with each site being one replicate
(equivalent to 1 farmer) with three treatments
involving maize \Z~'.;' mays), cassava (Maninhot esculenta)
and legumes such as cowpea (Vigna unguiculata),
pigeonpea (Cajanus cajan) and groundnut
(Arachis hypogaea). Maize and cassava spacing was
0.80"0.40 mana 1"1 m respectively, 0.40"0.40m for
pigeonpea , 0.80"0.80m for cowpea and 0,30"0.25 for
groundnut. The plot area covered 25 m 2 and the ~otal
area was 100m 2 , Other inputs i..cluded nitrogen
from the legumes and the crop residues.
The experimental treatments were intercrop legumes,
cassava and maize in rotation as follows:
Tl. Maize+Cowpea +Groundnut in the wet season
followed by maize in the dry season (this in
one year).
T2. Cowpea + Pigeonpea in the wet season and
sole maize in the dry season.
T3; Cassava+Cowpea and Groundnut, lasting in
the field with cassava until the end of the dry
season. This represents the normal farmer cropping
system.
40 kglha of P 20s was applied in all treatments since
the sandy soils are highly phosphorus deficient, expecting
that the Nitrogen input would corne from
the legumes . .
Results and Discussion
Ants destroyed groundnut because of late sowing
and the dry season maize was not sown because of
drought (long dry spell in the beginning of the season).
With little rain, cowpea did produce some but
very low yields. As it has been postulated by Parsons
and Howe, 1984 in Giller and Wilson (1991),
this grain legume has the ability to maintain lower
osmotic potential in it's leaves under water stress
conditions. The best performer among legumes was
pigeonpea that resisted the environmental stress
(rain, temperatures, low fertility).
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Grain legumes and Green Manures for Soil Fertility in Southern Africa