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

Table 9. Common pests on cowpeas as mentioned by
farmers
Zimuto Chihota Shurugwi
Aphids 75.9 58.5 77.9
Beetles 17 10.2
Worms 8.6 9.4 8.5
None 3.4 1.7 1.7
Termites and ants 3.4 7.5
Stemborers 1.7 1.9
Weevils 3.4 1.9
Others 3.4 3.8 1.7
Table 10. Solutions to some of the pest problems
suggested by farmers
Zimuto Chihota Shu rug wi
Chemicals 3.3 13.8 4.9
Traditional herbs 16.4 15.5 8.2
Cultural practices 11.5 6.9 6.6
00 nothing 68.8 63.8 80.3
Women made important decisions on the production
of legumes and minor crops, including cowpea.
Among the reasons why women farmers took this
role were; traditionally it's a woman crop, women
were responsible for ·providing food and relish in
the household, men perceived that cowpea was not
an important crop, women realized the importance
of the crop and that women sometimes made decisions
on farm operations in the absence of men.
Discussion
Area under legumes and cowpea
Compared to cereals, the area planted with legumes
in the three communal areas ranges from insignificant
to small portions of the farm (Tables 1 and 2).
Most of the cultivated land is put under maize because
itis the staple crop, followed by cash crops
like tobacco, paprika and cotton. however, most
farmers (99%) devote part of the farm to cultivation
of at least one legume crop among which are
groundnut, bambara or cowpea. The small area
planteo determines the modest contribution made
by legumes to the N budget on the farms. In most
~ommunal areas, biomass production is key to the
utilization of these high quality materials. The successful
use of these legumes in improving soil fertility
depends on the quantities of organic materials
available for use on the farm. Work done by Nhamo
et a1. (2002) has shown the importance of the
~mounts of organic materials available on the farm
in the adoption of some of these organic based soil
fertility technologies. Biomass production following
the planting of cowpea on these small areas at low
Table 11. Scoring on the utilization of cowpea by farmers
for domestic consumption
Zimuto Chihota Shurugwi
Porridge (Rupiza) . 3 3 4
Relish (Leaves) 2 2 3
Relish (Grain) 4 4 2
Boiled beans (Mutakura)
plant populations is insufficient to make a big impact
on the fertility status of soils.
Farmers in the study areas grew several crops including
small grains to spread the risk of crop failure.
Under unpredictable climatic conditions, smallholder
farmers use such strategies to ensure household
food security. Millets however are also important
in beer brewing for the traditional rituals.
Soil fertility benefits of cowpea
Farmers perceived that there were soil fertility benefits
and improved yields of maize grown after cowpea
(Table 6). The soil attributes linked to these improvements
varied from the observable soil colour
to the soil water holding capacity. Cowpea ranked
second after groundnut in residue production and,
hence soil improvement potential (Table 4). Most
farmers intercropped cowpea and maize or other
cereals. Intercropping maize and cowpea has been
reported to increase yields in some cases
(Olasantan, 1988; Jeranyama et al. 2000) and even
better yields have been reported in rotations where
there are no moisture competition effects (Kouyate
et al. 2000; Rao and Mathuva, 2000). However, few
studies have been conducted comparing the two
farming systems directly. Work done by Hardter et
a1. (1991) has shown that while mixed maizecowpea
cropping had lower yields than rotations,
continuous monocropping had the lowest productivity.
The reasons why farmers iritercrop are varied.
With regards to soil fertility, these can be explained
scientifically by the residual effects on cereals
following legumes in rotation and by the below
ground nutrient transfers that occur in the
rhizosphere in intercrops (Bandyopadhyay and De,
1986).
Incorporating legume residues to the soil improves
its fertility. Work done on legumes has demonstrated
the usefulness of legumes grown in rotation
with cereals in general (Giller and Wilson, 1991,
Giller 2001). For cereal/legume rotations to be successful,
a reasonable amount of legume non-grain
residue/biomass has to be produced and its management
has to be effeLi;ve. Residues generated by
legumes are in two forms; the roots (below ground)
and the stems and the leaves (aboveground) (Giller
and Wilson, 1991). The agronomic contributions of
the above and below ground portions of the cowpea
Grain Legumes and Green Manures for Soil Fertility in Southern Africa
123