Sustainable soil management options for Malawi: can smallholder farmers grow more legumes?

Abstract

Sole-cropped, unfertilized maize is the dominant cropping system throughout southern Africa. Yields have become stagnant and legumes are frequently advocated as an affordable option for resource poor farmers, to enhance productivity. Farmer participatory research was employed to test legume intensification as a means to improve maize-based systems in Malawi. A range of options were evaluated, from grain/legume intercrops of long-duration pigeonpea (Cajanus cajan) and groundnut (Arachis hypogaea) rotated with maize (Zea mays), to a relay green manure system of maize with Tephrosia vogelii (Fishbean). Two years of on-farm experimentation indicated that under on-farm conditions legume-intensified systems produced residues that contained about 50 kg N/ha per year, two-fold higher than sole-cropped maize residues. Grain yields from legume-intensified systems were comparable to yields from continuous sole maize, even in a dry lakeshore ecology. These preliminary findings were linked to farmer assessment, where farmers participating in the trials expressed strong interest in the technologies. Yet the probability of adoption remains uncertain. Associated surveys outlined constraints and trade-offs underlying technology choice, information that is not usually considered in conjunction with on-farm trials. Although the legumes were highly productive, farmers expressed worries about the marginal loss of maize production. While the trial performance was similar across regions, differences in market condition, farm resources and household composition appears to stimulate different technology choices. Farmers weigh the benefits of weed suppression and potential cash earnings, against the costs of seed, problems of seed access, labor requirements and problems of grain market access and price. Surveyed farmers commonly manage residues by burning. Promotion and experimentation with more efficient use of legume residues may offer higher short-term impacts than efforts to promote adoption of another cash crop. Ultimately, adoption and soil fertility benefits may depend on market returns to legume production. This study documents the value of researchers and farmers partnering in evaluation of technologies, adoption constraints and competing technology choices.

Improving Nitrogen Efficiency: Lessons from Malawi and Michigan

“…Three cropping systems were compared: (1) current practice, which is a maize continuous system using the average fertilizer rate of 18 kg N ha 1 from survey data (low-density potato intercrop at a 6:1 ratio of maize:potato was not possible to simulate given current model limitations), (2) recommended practice, which is a maize continuous system at the recommended rate of 69 kg N ha 1 , over threefold higher than current fertilizer use, and (3) integrated practice, which is rotation of a grain legume with maize; the recommended N fertilizer rate for the system in the second year is 69 kg N ha 1 minus legume N credit of 35 kg N ha 1 from residues incorporated after grain legume rotation. Pigeonpea was the grain legume of choice since it consistently has been shown to perform well under low soil fertility on smallholder farms and to produce residues containing 60 kg N ha 1 where we assume from N mineralization assays that 35 kg N ha 1 is available to subsequent crops [9,10]. This is similar to results from other Malawi studies of on-farm production of pigeonpea residues, although considerably less than is biologically possible [13,15].…”

“…Malawi cropping systems are constrained by a unimodal precipitation pattern that limits farmers to one crop per season and to an average area of land per farm holding of less than 2 ha [9] . Soils are Alfisols and Ultisols, generally sandy in texture and deficient in N status.…”

“…Maize (Zea mays) accounts for 60 to 80% of the area sown. The remainder of smallholder arable land is sown to tobacco (Nicotiana tabacum), groundnut (Arachis hypogaea), common bean (Phaseolus vulgaris), pigeonpea (Cajanus cajan), and, in highland sites, potato (Solanum tuberosum) [9]. Fertilizer is frequently applied 2 to 4 weeks after crop emergence.…”

Variable grain legume yields, responses to phosphorus and rotational effects on maize across soil fertility gradients on African smallholder farms

“…Legumes have the potential to contribute to the soil N budget through biological N 2 -fixation (BNF), and are potentially a cheap alternative to mineral N fertilizers for providing N to crops (Boddey et al 1997;Giller et al 1997). Grain legumes are more attractive to most smallholder farmers than other legume-based technologies, such as green manures, which do not contribute directly to income or food security (Giller 2001;Snapp et al 2002). However, most grain legumes have high N harvest indices and may only have a small or net negative contribution to the soil N budget (Giller and Cadisch 1995).…”

“…Major challenges exist to enhance productivity of soyabean and other grain legumes under smallholder farm conditions (Snapp et al 2002). Soils cultivated by smallholder farmers are predominantly infertile and sandy, with small contents of soil organic matter, available P and bases, and are also acidic.…”