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

PATHWAYS FOR FITTING LEGUMES INTO EAST AFRICAN HIGHLAND
FARMING SYSTEMS: A DUAL APPROACH
TILAHUN AMEDE
African Highlands Initiative (AHI) / Tropical Soils Biology and Fertility Institute of CIA T,
Code 1110, P. O. Box 1412, Addis Ababa, Ethiopia, T.Amede@CGIAR.ORG
Abstract
Food legumes have remained important components of various farming systems in Eastern Africa, but attempts to integrate
fodder legumes and legume cover crops (Lees) have been unsuccessful. Despite recognising their benefits as soil
fertility restorers and providers of high quality fodder, farmers remained reluctant to integrate legumes mainly due to
communitylfanner- specific socio-economic determinants. This paper is based on the experiences of the African Highlands
Initiative that has worked to integrate legumes in Areka in "the Ethiopian Highlands. The work has tried to understand
the processes of integration of legumes that have different uses, through participatory research. Areka has an elevation
of 1990 masl, and an annual rainfall of 1300 mm. The area is characterised by mixed subsistence fanning systems,
poor access to resources, intensive cropping, land shortage and soil degradation . A participatory evaluation of the
agronomic performance and adaptability of eight legumes was conducted for three consecutive years during the main
and short growing seasons, accompanied by extensive data collection on socio-economic determinants. Participatory experiel1ces
showed that the selection criterion of fanners went far beyond biomass production. The major biophysical
traits are performance of the species under a specific agroecology (characterised by yield, disease and pest resistance),
effect on soil fertility and the succeeding crop and its compatibility within the existing cropping system. Specifically,
farmers identified a firm root system, early soil cover, biomass yield, decomposition rate, soil moisture conservation,
drought resistance and feed value as important criteria. The total sum of farmers' biophysical criteria showed that Mucuna
followed by Crotalaria should be the best fitting species, but fanners finally decided on Vetch, the low yielder, due
to its fast growth and high feed value. The fanners' priority was for livestock feed rather than soil fertility. The final decision
of the farmers on whether and where to integrate a food legume into their temporal and spatial niches in the system
is dictated by their food habits, while for a non-food legume it depended on land productivity, fann size, land ownership,
access to markets and a need for livestock feed. The potential adopters of Lees and forage legumes were less than
7% of the fanners, while 91 % of the fanners integrated new cultivars of food legumes. A strategic combination of biophysical
and socio-economic determinants in the form of decision guides was suggested to facilitate the integration of
legumes into farming communities, and help development agencies and researchers to easily identify potential adopters,
learn about thl.:; criteria of choice and suggest an improved system of management. It may also help them to identify
niches or create niches, modify the existing systems and promote the technology for wider use.
Key words: Legumes, subsistence fanners, selection criteria, integration, decision guides
Introduction
Legumes playa pivotal role in nutrient cycling and
nutrient enrichment in many subsistence-farming
systems in Africa. They are considered drivers of
sustainable farming because they intensify the productivity
and interaction of soit crop, livestock,
people and other components. In most parts of Africa,
where livestock products are unaffordable, legumes
(especially bean, cowpea, pea, chickpea and
faba bean) are the major sources of protein. The
maize-based, banana-based and enset-based systems
are supported mainly by bean and cowpea as
major protein sources. Legume fodder, as crop residues
or hay, is also a high value feed for milking
cows, calves and draught oxen, especially during
the dry season and in times of high energy demand.
Legumes increase soil fertility through various
mechanisms. High quality legume fodder produces
a high quality manure that could improve soil fertility.
Legumes can also boost the nitrogen stock in the
soil through nitrogen fixation and nutrient release
from their organic residues. Some legumes also release
root exudates that may increase the availability
of unavailable/fixed nutrients, e.g. phosphorus,
through changing the rhizosphere pH and increased
activity by rhizosphere biota.
The increasing interest with organic farming in the
developed world and the challenge to decrease
costs of inorganic inputs to maintain soil fertility in
the developing world has focussed the attention of
researchers and policy makers towards legume
technology. Organic inputs from legumes could increase
crop yield through improved nutrient supply/
availability and / or improved soil-water hold-
Grain Legumes and Green Manures tor Soil Fllrtility in Southern Africa 21