Sustainable intensification of smallholder farms in Africa is highly dependent on enhancing biological nitrogen fixation
(BNF). Legume diversification of maize-based systems is a core example of sustainable intensification, with the food
security of millions of farm families at stake. This study highlights the constraints and opportunities associated with the
adoption of legumes by smallholder farmers in southern Africa. A two-part survey of households and farm fields (n=88)
was conducted in the Ekwendeni watershed of northern Malawi. Participatory research and education activities have
been underway for over a decade in this region, resulting in expanded uptake of a range of legume species as intercrops
and in rotation with the staple maize crop. Farmer adoption has occurred to a varying extent for soybean (Glycine max),
pigeon pea (Cajanus cajan), velvet bean (Mucuna pruriens) and fish bean (Tephrosia vogelii). Farmers, working with the
project valued pigeon pea and other legumes for soil fertility purposes to a greater extent than farmers not working with
the project. Legumes were valued for a wide range of purposes beyond soil cover and fertility enhancement, notably for
infant nutrition (at least for soybean), insect control, and vegetable and grain production for both market and home
consumption. Literature values for BNF in tropical legumes range up to 170kgNha−1 for grain and 300kgNha−1 for
green manure species; however, our field interviews illustrated the extent of constraints imposed by soil properties on
smallholder fields in Malawi. The key edaphic constraints observed were very deficient to moderate phosphorus levels
(range 4–142, average 33mgkg−1), and moderately acid soils (range pH 5.1–7.9, average 6.2). The per farm hectarage
devoted to legume production relative to maize production was also low (0.15 versus 0.35 ha), a surprising find in an area
with demonstrated interest in novel legume species. Further, farmers showed a strong preference for legumes that
produced edible grain, regardless of the associated nutrient removal in the harvested grain, and did not sow large areas to
legume crops. These farm-level decisions act as constraints to BNF inputs in maize-based smallholder cropping systems.
Overall, we found that legume productivity could be enhanced. We documented the value of policies and educational
efforts that support farmers gaining access to high-quality seeds, amendments for phosphorus-deficient soils, and
promotion of multipurpose legumes that build soils through leafy residues and roots, as well as providing grain for food
security and sales.
Key words: integrated soil fertility management, smallholder farmer, sustainable intensification