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

Abstract
PROMOTING NEW BNF TECHNOLOGIES AMONG SMALLHOLDER
FARMERS: A SUCCESS STORY FROM ZIMBABWE
SHEUNESU MPEPEREKI 1 and ISHMAEL POMPI 2
1Department of Soil Science and Agricultural Engineering, University of Zimbabwe,
PO Box MP167, Mount Pleasant, Harare and
2Agronomy Research Institute, Department of Research and Extension,
Ministry of Agriculture, PO Box CY550, Causeway, Harare, Zimbabwe
Biological nitrogen fixation (BNF) contributes significant amollnts of N into both managed and natural ecosystems and
forn:s the basis for the age-old practice of rotating legumes with other crops. Benefits of legume N fixation include protein
nutrition, soil fertility improvement, savings on fertilizer costs and cash income from sale of crop surpluses. The
packaging and use of superior N-fixing rhizobial strains as commercial legume inoculants is a relatively cheap costeffective
technology widely adopted by large-scale but not smallholder farmers in Zimbabwe. We report on a promotion
program that used soyabean as a vehicle to convey the multiple benefits of BNF technologies to poor smallholder farmers
through a multi-faceted research-extension-promotion effort. The primary objective was to strengthen rural food security
of smallholder farmers through exploitation of soyabean BNF for soil fertility improvement against rising input
costs. The main elements of the promotion strategy included training farmers and extension staff in technology applica­
'tion, demonstration of the tangible multiple benefits and facilitation of input/output marketing, all backed by a parallel
program of adaptive research. The.basic promotion concept used was that of creating a closed loop with four links: training
(in BNF technology application), production (of soyabean), processing and marketing (TPPM). Coordination of
stakeholder activities was and continues to be a critical component of the promotion effort. A conceptual framework linking
various elements (BNF technology, food security, soil fertility, cash income) was used to guide and focus both the
promotion and research components. The rate of adoption of soyabean BNF among smallholders has been near exponential
(from 50 farmers in 1996 to more than 10,000 in 2000). This paper outlines the conceptual framework and mechanisms
used in the promotion of soyabean technologies, the responses of smallholder farmers and the prospects for wider
scaling up.
Key words: Soya bean, smallholder farmers, BNF, soil fertility improvement
Introduction
Nitrogen deficiency is the main limiting factor for
high cereal yields iIi sub-Saharan Africa and'yet the
majority of smallholder farmers use very little mineral
N fertilizer. Biological nitrogen fixation (BNF)
contributes significant quantities of nitrogen (N) to
both natural and managed ecosystems and offers a
relatively cheap alternative source of N for resource-poor
farmers. Exploitation of BNF technologies
in African farming systems requires the identification
of appropriate N-fixing legumes that have
multiple benefits to ensure adoption by risk-averse
rural communities. There is need to develop a research
agenda that identifies appropriate BNF technologies
(e.g. effective legume-rhizobium combinations)
that can be readily adopted by farmers with
immediate demonstrable benefits to ensure adoption.
Such research efforts will need to be linked to
appropriate extension programs that ensure that
target commlmities benefit in tangible ways.
Traditional legumes such as groundnut (Arachis hy-
pogaeae), cowpea (Vigna unguiculata) and bambara
nut (Vigna jubterranea) that rely on BNF and contribute
residual fertility to soils are low-yielding and
are often viewed as minor crops. Yields of these legumes
have failed to respond consistently to inoculation
with commercial rhizobiaI strains. Soyabean, a
relatively new legume in Africa, responds well to
rhizobiaI inoculation and fixes large amounts of N
even in marginal soils (Kasasa, 2000; Musiyiwa,
2001). The multiple benefits of soyabean include soil
fertility improvement, protein nutrition for humans
and livestock and cash income from sales of grain
and processed products. Soyabean is now grown in
several parts of sub-Saharan Africa including Malawi,
Nigeria, Zambia and Zimbabwe where it is
making significant contributions to rural livelihoods.
Due to limited inoculant production capacity
in most African countries, promiscuous soyabean
varieties that effectively nodulate with indigeno\.!s
rhizobia have been successfully grown without inoculants
demonstrating their potential for conveying
the benefits of BNF to poor and marginalized
communities (Mpepereki et al. 2000).
Grain Legumes an,d Green Manures for SO'il Fertility in Southern Africa
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