Green Manure/Cover Crop Technology in Eastern and Central Uganda: Development and Dissemination

Abstract

In 1992, Ugandan National Agricultural Research Organization along with International Center for Tropical Agriculture researchers from Kawanda Agricultural Research Institute initiated collaborative research with farmers in Uganda. Five villages in the vicinity of the Ikulwe District Farmers Institute in Iganga district of eastern Uganda were included. This area represents the traditional banana (Musa sp. L.)-coffee (Coffea L.)-based systems of the Lake Victoria Crescent agro-ecological zone. It has a mean annual rainfall of 1255 mm in a bimodal distribution and soils that are variable but typically have low total soil N as well as low P availability in Ikulwe. Banana, bean (Phaseolus vulgaris L.), sweet potato (Ipomoea batatas [L.] Lam.), cassava (Manihot esculenta Crantz), groundnuts (Arachis hypogaea L.) and maize (Zea mays L.) are important food crops. The approach was participatory, systems oriented and interdisciplinary. Research activities on green manure/cover crops (GMCCs) consisted of some designed by farmers and researchers, and some farmers’ own experimentation. Farmer-researcher trials indicated that yields of the GMCC species were reduced 40–70% when intercropped with a food crop as compared to sole crop production and that yields of food crops were reduced 61–87% when intercropped with Crotalaria ochroleuca G. Don. In contrast, maize grain yield response in the first season following sole-crop GMCC production ranged from 0 to 240%. These trials also indicated that Mucuna pruriens (L.) DC. and Lablab purpureus (L) Sweet were best for weed suppression and for control of soil erosion, that tillage and weeding requirements can be much less following GMCCs and that maize can often be planted directly in the holes left from uprooting Mucuna and Lablab, reducing labour requirements the following season. Land productivity was not improved with alley cropping. Farmers initiated trials on their own, such as on Tephrosia vogelii Hook. f. to control mole rats, which indicated effective control and resulted in significant adoption by neighbouring farmers. Other farmer experimentation focused on intercropping GMCCs with coffee, banana with Canavalia ensiformis (L.) DC., cassava and sweet potato, and Mucuna with maize.

Researchers’ interviews with 19 of the farmer-researchers indicated that improvement of soil fertility followed by suppression of weeds was the most frequently mentioned positive feature of GMCCs. Uprooting of the mature GMCC plants was easiest for Canavalia. Lablab was most preferred for forage production. The legumes were similarly mentioned as effective in reducing soil erosion. Farmers frequently expressed concern about the climbing tendency of Mucuna as well as Lablab. Lablab produced little, but edible, seed, while Canavalia and Mucuna produced much inedible seed. Crotalaria was frequently observed to be laborious to cultivate. Canavalia, Crotalaria, Lablab and Mucuna differed little from one another in intercrop compatibility with banana, maize and cassava. Canavalia was more compatible with sweet potato than were other legumes. Information from on-station trials, formal on-farm trials and farmers’ own experimentation was integrated to develop a decision guide on the use of GMCC legumes. Researchers facilitated the dissemination of GMCC technology through informal seed exchanges, printed materials, farmer group visits to Ikulwe, agricultural shows, government and non-government extension, farmer experimentation mini-kits and provision of materials to stockists of agricultural inputs. A banana-Mucuna-dairy system and the Tephrosia system for mole rat control have been the most adopted.