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Improved varieties of legumes adapted to nutrient deficiency have the potential to improve food security for the poorest farmers. Tolerant varieties could be an inexpensive and biologically smart technology that improves soils while minimizing fertilizer costs. Yet other technologies that improve productivity and appear to be biologically sound have been rejected by farmers. To translate benefits to smallholder farmers, research on low-nutrient tolerant genes and crop improvement must keep farmer preferences and belief systems in the forefront. We review farmer participatory research on legume-intensification and soil fertility management options for smallholder farmers in Africa, including recent results from our work in Malawi and Kenya. We suggest that indeterminate, longduration legumes are the best bet for producing high quality residues, compared to short-duration and determinate genotypes. This may be due to a long period of time to biologically fix nitrogen, acquire nutrients, photosynthesize and grain fill. Also, the indeterminate nature of long-duration varieties facilitates recovery from intermittent stresses such as drought or pest pressure. However, indeterminate growth habit is also associated with late maturity, moderate yield potential and high labour demand. These traits are not necessarily compatible with smallholder criteria for acceptable varieties. Malawi women farmers, for example, prioritized early maturity and low-labour requirement, as well as yield potential. To address complex farmer requirements, we suggest the purposeful combination of species with different growth habits; e.g. deep-rooted indeterminate long-duration pigeonpea interplanted with short-duration soyabean and groudnut varieties. On-farm trials in Malawi indicate that calorie production can be increased by 30% through pigeonpea-intensified systems. Farmers consistently indicate strong interest in these systems. In Kenya, a 55% yield increase was observed for a doubled-up pigeonpea system (a double row of pigeonpea intercropped with three maize rows) compared to traditional, low density intercrops. However, the need for improved pigeonpea varieties with high intercrop suitability, including reduced early branching, was highlighted by a farmer preference study in the same area. These examples illustrate the potential for participatory research methodologies to drive biophysical research in farmer-acceptable directions.

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This chapter reviews evidence of the impacts of agroecological farming practices on climate adaptation and mitigation. Farm diversification has the strongest evidence for its impacts on climate change adaptation. The evidence for agroecology’s impact on mitigation in LMICs is modest and emphasises carbon sequestration in soil and biomass. Agroforestry has the strongest body of evidence for impacts on mitigation. Locally relevant solutions produced through participatory processes and the co-creation of knowledge with farmers has improved climate change adaptation and mitigation. Knowledge gaps were found in regard to agricultural climate change mitigation, resilience to extreme weather, and agroecology approaches involving livestock, landscape redesign and multi-scalar analysis. There is a need to assess the performance of agricultural development using an outcome-based approach based on agroecological principles and climate change adaptation and mitigation indicators in order to guide donor and national investment. Moreover, direct investment and the scaling of practices for which the current evidence is strongest are needed. These include: (1) agricultural diversification, agroforestry and local adaptation; (2) increase action around resilience to extreme weather and climate change mitigation outcomes in LMICs and build the capacity of policymakers, scientists and institutions from the global South to work on these issues; and (3) compare the cost-effectiveness and outcomes of agroecology approaches with other agricultural development interventions at multiple scales, including the valuation of environmental and social benefits to better evaluate alternative approaches to sustainable agriculture.

Implementing sustainable production practices to rehabilitate soils is a grand challenge of our day, particularly for resource-poor farmers. The West African Sahel requires attention to balancing the need for increasing agricultural production against harsh environmental conditions. While there is much research documenting technologies for soil regeneration in the Sahel, there has been limited focus on how agricultural practices contribute or exacerbate these efforts. Previous assessments of agricultural practices in this region have been largely descriptive, and some soil ameliorating practices have been promoted with little empirical evidence on their effectiveness. Here we systematically review the literature on soil fertility and conservation practices that have been studied within West African Sahelian agricultural systems. We identified practices in the West African Sahel that have been tested to improve soil fertility and reduce land degradation, and summarized the outcomes of these practices. A unique contribution of this review is the assessment of site-specific conditions and contexts under which practices are most effective in studies which recorded these specific characteristics. We found that research in this area is dominated by chemical fertilizer and organic amendment practices, with moderate to few studies focused on soil and water conservation, crop diversification, or agroforestry. Additionally, most studies consisted of single practices rather than combining practices that target the range of biophysical limitations farmers face in agricultural production. These limitations highlight the need for increased research testing combinations of practices across long-term on-farm studies to generate stronger evidence of conditions under which practices best perform. These findings provide key lessons for research and extension on sustainable agricultural management under the challenging conditions of the Sahel.