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

Questions and Answers
.Identification of Best Bet Legumes for On-farm Performance as Grain Legumes,
Intercrops, Rotations, and Green Manures
.
To Webster Sakala and Wezi Mhango
Q: In the intercrop and rotation practices on maize
cultivation, what levels of additional fertilizers were
added apart from the green manures?
A: On average, it was half the requirement of the
maize crop, which was around 40 kg N ha- 1 , but it is
difficult to give a specific figure because we looked
at several studies.
Q: Results of green manures and grain legumes
appear to be promising in Malawi. What is the
uptake rate of these technologies among
smallholder farmers? What were the yields of
soyabean intercropped with maize? I thought that
soyabean is very sensitive to shading.
A: The grain legumes/green manures are currently
being promoted amongst the smallholder farmers.
The farmers make choices depending on the
resources that they have, e.g. land, so that if they
have less land they go for intercropping, and for
improved fallows or rotation if land is more
plentiful. Soya bean is usually grown in pure
stands.
Q: As early incorporation of green manures may
cause an N loss due to early showers (leaching), the
nutrient supply could have been better if the
legumes were incorporated late, to synchronize the
peak N demand of maize with nutrient release.
What is your comment o,n that?
A: This is not a problem in Malawi because of the
nature of our rainfall where after incorporation we
experience a 6-8 month dry season before the next
growing season. This may be a problem in countries
where they receive some heavy showers before the
next crop season.
To Dennis Friesen, et al.
Q: It looks like you do not have a soil fertility
problem in East Africa because you get up to 6 t/ha
maize grain yield. At one site you get almost 5 t/ha
without fertilizer and 6 t/ha with fertilizer,
displaying a low response to fertilizer.
A: Generally those high maize yields without
fertilizer were obtained in trials conducted on
station where the soils are better and where there
has been a history of fertilizer use. Yields on farm
were generally closer to the mean yields reported
for the region (1-2 t/ha) L with some exceptions in
high potential areas.
Q: Did you apply any fertilizer when you
intercropped and how much?
A: In general, DAP is applied to the maize adjacent
to the planting hole at the recommended rate, which
varies in the region (generally around 46 kg P20S /
ha).
Q: Intercrops are notoriously difficult to manage,
and where they work can depend on various site
effects. Yet some have been very successful. How
can we move towards making predictions of where
they will succeed, and recommendations for their
management?
A: Factors that affect the growth of the intercrop
such as moisture, soil fertility, light penetration of
the maize canopy, can probably be used to predict
intercrop growth using a modelling approach.
However, farmers need rules of thumb to predict
when to 'plant the intercrop, what maize varieties to
intercrop into, etc. Perhaps modelling can help to
develop these guidelines.
To Nhamo Nhamo, et al.
Q: Did you check the specific names for the cowpea
varieties that the farmers received from donors?
A: Yes but we asked for the local names for these
varieties, so if it was introduced by the donor and
the farmers did not remember then we could have
missed them.
To Pauline Chivenge, et al.
Q: It would be useful to establish how the various
legumes perform under amount of rainfall. Did you
conduct correlation analysis for rainfall?
A: No, the drought did not allow that.
Q: The low available P in your soil is not consistent
with the high biomass yield. Could this observation
suggest that the plants are obtaining P from
insoluble P soil sources?
A: Quite right, but also the northern part of Zambia
where these yields were obtained received very
good rainfall.
Grain Legumes and Green Manures for Soil Fertility in Southern Africa
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