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

• Conduct more research to measure and value
other benefits
• Develop policy instruments (ptjce increases and
decrease in interest rates) to support green manures.
2. To raise the economic potential of Green Manure,
we need to address:
a) Market constraints
• Low yields
• Poor quality
• Gap, factory vs. farm gate
• Lack of information
• Government policies
• Local industrial use.
b) Farm constraints
• Poor fit into cropping system
• Poor input market
• Communication problems (poor marketing).
3. Learn from socio economic analysis
• Policy and development planning is vital
• Assess the conditions under which cereal legume
rotations and intercropping are most feasible
in the smallholder sector
Appreciate that cowpea appears the most attractive
of all legumes to Zimbabwe farmers.
Working Group Reports
Biophysical Work
244
1. Benefits of the Technologies and the Work
Completed
• Legumes (grain legumes as well as green
manures) increase soil fertility and productivity
and therefore the grain yields of subsequent
maize crops.
• Green manures tended to give more consistent
and substantive effects on subsequent maize
yields than did grain legumes. Green manures
can increase maize grain yields by as much as
385%, or 2.5 - 3.0 t/ha on farmer's fields in
Malawi.
• The yield benefit of N from a legume can be due
to an increase in below ground biomass, as
appears to be the case with soyabean.
• Improvements in maize productivity have
important consequences for diversification and
food security.
• Various types of economic benefits accrue,
including the reduction in amounts and costs of
inorganic fertilizer ·inputs and extra grain and
cash.
• Weed suppression may result (and can be especially
beneficial with Striga). There may be important
labour savings for weeding, especially
in high rainfall areas.
• There is a potential benefit with improved soil
physical properties (aggregates, infiltration, porosity,
soil loss/surface runoff, water use efficiency).
• Fodder resources may increase also.
2. Gaps and Limits with Existing Work and
Knowledge
Reviews and Synthesis:
• The current reviews presented for Malawi and
Zimbabwe cover green manures but not the
grain legumes.
• A review of Zambian work highlights the need
for widespread dissemination of green
manures.
• Not all the lessons from the comprehensive
work presented from other regions of Africa,
particularly West Africa, are directly
transferable to Southern Africa. The
environments (and socio-economics) are
different.
Soil Science:
• There is inadequate measurement of soil. physical
properties and related issues like reduced
tillage.
• Non-nitrogen benefits of legumes on below
ground biomass, texture, Ca/Mg balance and P,
cations, need more attention, as does SOM and
C sequestration.
• We need to pin down the fate of N in the system.
What goes into the plant anq what elsewhere?
This also involves nutrient balances and
partitioning of N in pools.
• Far more information is needed on mycorhiza/
P interactions for us to provide appropriate
recommendations.
• The evaluation of long-term benefits and sustainability
aspects need attention.
Legume Germplasm:
• The genetic base of species/provenances we
have worked with has been too narrow. We
need to screen more of these. What approac.hes
should be used and where should screening be
done?
• Link up with breeders more often. They need to
work on issues that we are already working on
and we need to help focus their work onto new
useful traits.
• Need to inoculate with rhizobium/mycorhizae
(where, which legumes, and with what?).
• Alternative uses of green manures, as seeds and
firewood, need to be determined.
Grain legumes and Green Manures for Soil Fertility in Southern Africa