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

ust growth habit that enhances its competitive
ability for growth limiting factors. Gilbert (1998) reported
that Mucuna can be excessively competitive
with maize because it has an aggressive climbing
growth habit. When maize is intercropped with velvet
bean and established at the same time, interspedes
competition increases, particularly at later
stages of growth. For instance, there was no difference
in maize leaf area between the sole maize and
the intercropped maize at two and four weeks after
planting. During this period, interspecies competition
of the intercrop appears not affect maize leaf
area. Probably plants were too young to interfere
with each other but as they grow, competition begins
that reduces leaf area at later stages of growth.
When legumes were planted two weeks later, S. asiatica
counts were generally higher than when legumes
were planted at the same time as maize. This
trend was also observed in the field experiment.
Legumes caused suicidal germination of S. asiatica
when planted at the same time and this could have
reduced the S. asiatica numbers. When maize and
legumes were planted two weeks apart, more S. asiatica
plants emerged as the parasite that germinated
from the maize stimulant successfully attached to
the maize roots. Carsky et al (1994) postulated three
reasons for reduction of Striga when intercropped
with cowpea. These include suicidal germination of
Striga, release of nitrogen into the soil and shading
which consequently lowers soil temperature. These
reasons were also supported by Musambasi et al
(2002) wh0 suggested that legumes could provide
shade which smother and kill S. asiatica. These reasons
can therefore be used to extrapolate the results
obtained. Planting legumes and maize at the same
time, allowed legumes to quickly develop a crop
canopy that produced a shading effect, lowering the
soil temperatures that could have affected the emergence
of S. asiatica. Babiker et al (1993) found thaI,
the density of Striga hermontheca was reduced in a
sorghum-dolichos intercrop. Probably maize is a
better germination stimulant than the legumes
tested. The S. asiatica that germinates due to the legumes
is of no significance as compared to S. asiatica
that maize stimulates and supports. However, the
time of planting the green manure makes the difference
in terms of S. asiatica numbers. Similar trends
were observed with S. asiatica dry weights.
There was no grain yield from the field experiment
owing to the poor rainfall distribution. Yield from
the pot experiment was not ,influenced by the green
manure legumes or their time of planting. It would
be interesting to find out how these factors influence
yield in a normal season under field conditions.
The competitiv~ effects of the green manure
legumes experienced during the fourth to the sixth
week after planting were not enough to significantly
reduce yield in the pot experiment.
Recommendations
Green manure legumes intercropped with maize
should be planted two weeks later to reduce competition
among component crops. For S. asiatica, the
green manure legumes should be established at the
same time with maize in a field heavily infested
with S. asiatica. A legume that does not compete
with maize for resources should be planted at the
same time as maize. The experiment needs to be
conducted again in another season to get conclusive
results in the field.
Acknowledge,ments
We extend our gratitude to the Rockefeller Founda­
tion Forum on Agricultural Resource Husbandry
for funding this work.
References
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E. EI Mana, and S.M. EI Tayeb, 1993. Striga hermontheca
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Grain Legumes and Green Manures for Soil Fertility in Southern Africa