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

GRAIN LEGUMES AND GREEN MANURES IN EAST AFRICAN MAIZE
SYSTEMS - AN OVERVIEW OF ECAMAW NETWORK RESEARCH
DENNIS K. FRIESEN 1 , R. ASSENGA 2 , TESFA BOGALE 3 , T.E. MMBAGA 4 ,
J. KIKAFUNDA 5 , WAKENE NEGASSA 6 , J. OJIEM 7 and R. ONYANG0 8
1CIMMYT/IFDC, Nairobi, Kenya;
2Agricultural Research Institute-Mlingano Tanzania;
3Jimma Agricultural Research Center, Jimma, Ethiopia;
4Selian Agricultural Research Institute, Arusha, Tanzania;
5 Namulonge Agriculture and Animal Production Research Institute, Kampala, Uganda
6Bako Agricultural Research Center, Bako, Ethiop;a;
7Kakamega Regional Research Center, KARl, Kakamega, Kenya, and
8Kitale National Agricultural Research Center, KARl, Kitale, Kenya
Abstract
The Eastern and Central Africa Maize and Wheat (ECAMA W) Research Network, established in 1996, is one of 18 networks
operating under the Association for Strengthening Agricultural Research in Easterna.nd Central Africa
(ASARECA). ECAMA W addresses constrain:s to maize and wheat production in the ten ASARECA member countries
where maize is the number one priority crop and soil fertility is ranked as one of the principal constraints to improved
maize productivity and production. Nitrogen (N) is the most limiting nutrient in the region yet smallholder
farmers use very little fertilizer inputs due to high cost, poor infrastructure and risk due to climatic uncertainty. Legumes
in systems with maize are a potential alternative source of N for the maize crop. During the past 5 years, the
ECAMA W Network has funded 12 small ~rant projects dealing with green manure and grain legumes in systems with
maize. Network collaborators have implemented some 24 on-station experiments and 195 on-farm trials to evaluate and
identify suitable adapted grain legume and green manure species, and to quantify their impact on maize production in
systems including intercrops, relay crops and rotations. Some 12 legume species were evaluated for nodulation, ground
cover, resistance to pests and diseases, biomass production, seed production, etc. in the moist and dry mid-altitude, and
lowland ecologies of Ethiopia, Kenya, Tanzania and Uganda. Mucuna pruriens, Canavalia ensiformis, Crotalaria
ochroleuca and Dalicos lablab were the most widely adapted and most effective N providers, although other species
were 10caUy more suited. Green manure legumes intercropped with maize had no significant beneficial effects on maize
grain yields and, depending on their aggressiveness, sometimes significantly reduced maize yields. Green manure biomass
praduction was reduced in intercrops and more so when relayed into maize. Depending on the degree of growth
suppression and the duration offollow-on growth permitted after the maize harvest, green manures had either little or
substantial effects on maize yields in the following season. The effects of green manures rotated with maize. had more
consistent and substantive effects on subsequent maize yields with increases as much as 385%, or 2.5-3.0 t/ha, on farmers'
fields. Grain legumes, including soybean, cowpea, green gram and pigeonpea, had little beneficial or negative effect
on maize productivity whether grown as intercrops or in rotations. Farmers' reactions to green manures was mixed,
from reluctance to plant a crop which produced no food to appreciation of the weed suppressing effects and soil fertility
gains they provided. A frequent question regarded the palatability of mucuna and canavalia seed. Despite considerable
exposure to green manure legumes, farmers have been slow to adopt them into their farming systems. On the other
hand, grain legumes, which produced a consumable or marketable product, were highly valued by farmers.
Key words: ECAMA W Network, legume adaptation, intercropping, relay crops, rotations
Introduction
Maize is grown on more than 7.6 M hectares in East­
ern and Central Africa with an average yield less
than 1.3 t/ha (compared to a potential of 4.5-7 t/ha)
(Pingali,2001). Average per capita consumption of
maize grain is 50 kg, but it ranges from 12-103 kg
per person. Given the large area planted, and its
importance as a food and cash crop, maize was
id~ntified as the number one priority for regional
research by the Association for Strengthening Agricultural
Research in Eastern and Central Africa
(ASARECA). Low soil fertility, especially nitrogen
(N), is one of the principal constraints to increased
maize productivity in the region (ECAMA W, 1999).
Fertilizer use is less than 10 kg/ha/yr (Bumb and
Grain legumes and Green Manures for Soil Fertility in Southern Africa 113