Effects of management practices on legume productivity in smallholder farming systems in sub-Saharan Africa

Legumes play a key role in food and nutrition security, providing livestock feed and contributing to soil fertility, in mixed smallholder farms in sub-Saharan Africa (SSA). The environmental conditions under which smallholder farming is practiced are highly heterogeneous with large differences in management practices among farms resulting in variable legume productivity. A meta-analysis based on 128 publications was conducted to quantify the effects of intercropping, inoculation with rhizobia, minimum tillage and phosphorus application on legume grain and biomass yield and the amount of biological nitrogen fixation in a range of SSA contexts. To further explain the heterogeneity in the results, legume species, type of inoculant, P-application rate, altitude, rainfall, soil characteristics and non-legume companion crops were used as moderators. lntercropping as compared to sole cropping reduced legume biomass and grain yields to varying extents, although the total land equivalent ratio for the sum of the intercrops was higher than 1 (1.2-1.9)in all cases. Expressed as the relative land equivalent ratio (rLER) intercropping affected pigeonpea grain yield the least (rLER 0.9) and faba bean the most (rLER 0.3). The non-legume companion crops explained some of the heterogeneity where maize and sorghum significantly reduced the legume yields. Inoculation and P application increased legume grain and biomass yield and moderators such as legume species, type of inoculant, soil organic carbon and soil pH further explained the different effects of the management practices on legume productivity. Minimum tillage had no effect on legume productivity. although less data were available than for the other practices. We conclude that intercropping with legumes improves overall productivity and that application of P fertilizer and inoculants increase legume grain and biomass yield. The effect varies with crop species, soil type and other environmental conditions, and this needs to be factored into tailored recommendations supporting decision making in smallholder farming

Grain legumes and dryland cereals contribute to carbon sequestration in the drylands of Africa and South Asia

Grain legumes and drylands cereals including chickpea (Cicer arietinum), common bean (Phaseolus vulgaris), cowpea (Vigna unguiculata), groundnut (Arachis hypogaea), lentil (Lens culinaris), pigeon pea (Cajanus cajan), soybean (Glycine max), finger millet (Eleusine coracana), pearl millet (Pennisetum glaucum) and sorghum (Sorghum bicolor) are the leading sources of food grain in drylands of Africa and South Asia. These crops can help smallholder agriculture to become more resilient, productive, and profitable, but their quantitative impact on carbon sequestration is unknown. The aim of this review study was to quantify their contribution to carbon sequestration across the drylands of Africa and South Asia based on 437 publications with 1319 observations in studies conducted across 32 countries. Cropping systems with grain legumes showed the greatest increase in soil organic carbon (SOC) concentrations, while cereals (and pigeon pea) gave the largest amount of aboveground carbon stock (>2 Mg C ha 1). Estimated carbon stock in post-harvest residues of these crops was 1.51 +/- 0.05 Mg C ha 1 in Africa and 2.29 +/- 0.10 Mg C ha 1 in South Asia. These crops produced more aboveground carbon, and significantly increased SOC, when grown as intercrops. Soils with low initial SOC (32%) showed the greatest potential for carbon sequestration when cropped with grain legumes and dryland cereals. This study is the first of its kind to provide evidence that grain legumes and drylands cereals improve carbon sequestration across Africa and South Asia

Farmer perceptions of legumes and their functions in smallholder farming systems in east Africa

Legumes play an important role in sub-Saharan Africa (SSA) farming systems through the provision of food, feed, fuel, income and a range of biophysical benefits, such as soil fertility enhancement and erosion control. However, their full potential is not being realized. The purpose of this study was to assess farmers’ perceptions and knowledge towards legumes and the rationale of farmers for current legume production practices using a survey of 268 farmers in the Democratic Republic of Congo and Kenya. Most of the farmers had some knowledge of legumes and their characteristics. However, they had little knowledge of some key functions, including soil erosion control and soil fertility improvement. Most farmers relied on radio and other farmers for legume-related information. Farmers with relatively large livestock holdings ranked provision of livestock feed as an important legume function. We conclude that farmers put more value on short-term benefits of legumes including food and income than long-term benefits such as natural resource management and thus grain legumes are more readily identified by farmers than forage species. Also, we conclude that farmers require more than just information about legumes to increase uptake, they also require improved market access to procure inputs and sell products to realize other benefits that are associated with growing legumes

Conservation agriculture as a climate change mitigation strategy in Zimbabwe

There is a need to quantify agriculture’s potential to sequester carbon (C) to inform global approaches aimed at mitigating climate change effects. Many factors including climate, crop, soil management practices, and soil type can influence the contribution of agriculture to the global carbon cycle. The objective of this study was to investigate the C sequestration potential of conservation agriculture (CA) (defined by minimal soil disturbance, maintaining permanent soil cover, and crop rotations). This study used micrometeorological methods to measure carbon dioxide (CO2) flux from several alternative CA practices in Harare, central Zimbabwe. Micrometeorological methods can detect differences in total CO2 emissions of agricultural management practices; our results show that CA practices produce less CO2 emissions. Over three years of measurement, the mean and standard error (SE) of CO2 emissions for the plot with the most consistent CA practices was 0.564 ± 0.0122 g CO2 m-2 h-1, significantly less than 0.928 ± 0.00859 g CO2 m-2 h-1 for the conventional tillage practice. Overall CA practices of no-till with the use of cover crops produced fewer CO2 emissions than conventional tillage or fallow

Integrating legumes in mixed crop-livestock systems in east Africa: Farmers' perceptions, ecosystem services and support for decision making

Challenges faced by smallholder farmers in east Africa include limited access to inputs, small farm sizes, and erratic rainfall patterns. Legume intensification and species diversification have been recommended for improving food and nutritional security, controlling soil erosion, improving soil fertility, supplying income and providing fuel. The aim of the thesis was to assess the various contributions legumes make in integrated crop-livestock systems and to facilitate their efficient use. The approaches used included: 1) an on-farm survey of 268 farmers in Kenya and Democratic Republic of the Congo to assess farmers’ perceptions of legumes and their functions; 2) a metaanalysis on the effects of crop management practices on legume productivity and biological nitrogen fixation (BNF) in sub-Saharan Africa; 3) an on-farm experiment in Kenya investigating the effects of crops and crop mixtures including legumes on soil erosion control; and 4) providing inputs from literature review and experimental results to further develop the LegumeCHOICE decision support tool. Results showed that farmers appreciated legumes more for their food and income functions than for provision of fodder, fuel, soil fertility or erosion control. Furthermore, according to survey work, the concept of “legumes” had little meaning for farmers. The metaanalysis showed that crop management practices directly influenced legume productivity. Intercropping increased the total land equivalent ratio (LER). Focusing on the legume component, pigeon pea (Cajanus cajan) had a relative LER of 90%, while for species such as groundnut (Arachis hypogea) and common bean (Phaseolus vulgaris) the figure was around 60%. Inoculation and phosphorus (P) application increased legume grain and biomass yield, and species and soil type helped explain the variation of legume productivity in response to those management practices. Inoculation also increased the amount of nitrogen (N) fixed by legumes. Experimental work showed that incorporating different crop types and crop mixtures with legumes increased rainfall infiltration and earthworm population, and reduced runoff and soil erosion. Calliandra hedgerows, mulching and sole Mucuna reduced soil erosion and runoff more than maize/common bean intercropping. Developing literature-derived values as a complement to the expert scores, which presently underlie the LegumeCHOICE tool improved the relationships between the scoring and actual provision of food, livestock feed and soil fertility improvement using grain and biomass yield and BNF as proxies. This thesis shows that farmers in east Africa have some knowledge about legumes although their perception of the various functions legumes provide is limited. Despite heterogeneity of smallholder farming systems, legumes respond consistently to intercropping, inoculation and P-application. Combining literature values with expert scores enhanced the validity of the LegumeCHOICE tool for supporting farmer decision making

Weed Management in Zimbabwean Smallholder Conservation Agriculture Farming Sector

Weed management is one of the major constraints in the Zimbabwe smallholder farming sector contributing to smallholder poor yields, hence there is need to identify cropping systems that have potential to reduce weed pressure while improving crop yields. Conservation agriculture has been suggested as one of these farming systems. The implementation of CA three key principles reduces weed pressure even when the use of herbicides is minimised. Crops included in crop rotations, intercropping or relay cropping may have faster growth rate than weeds hence, have a comparative advantage over weeds. Maintenance of permanent soil cover through crop residues impedes weed germination thereby reducing weed population. Elimination of ploughing also reduces the chances of bringing buried weed seeds to the surface where their chances for germination are high. Hence, some seeds lose viability thus reducing weed density. Weed seeds accumulate at the surface, when allowed to set seed, increasing their exposure to predation resulting in reduction of weed density over time. The use of herbicides ensures that the fields are weed free as the season’s progress thus ensuring better yields at the end of each growing season. Hence, weeds are reduced in CA systems over time despite the weeding option used

Crop Residue Management in Conservation Agriculture Systems in Zimbabwe Smallholder Farming Sector: Importance, Management Challenges and Possible Solutions

Conservation agriculture (CA) is promoted as a cropping system that has potential to alleviate poor crop yields in smallholder farming while protecting the environment. It involves maintenance of permanent soil cover, diverse crop rotations and/or interactions; and minimum soil disturbance. CA is associated with crop residue management challenges due to low crop biomass yields and crop-livestock interactions in Zimbabwean smallholder farming sector. There is competition on crop residue uses causing challenges in retaining adequate crop residues for full benefits of using residues to be realised. Among the crop residues management options fencing fields reduces the chances of crop residues grazing by free roaming cattle during the dry season. Construction of rakes to pile up crop residues where cattle cannot access has been practiced in some communal areas. Farmers have practised the system of taking the crop residue harvest to homesteads into protected areas to reduce risk of grazing. Farmers may use fences around fields to reduce access into fields. However, all these management options require an investment from the farmers who are resource constrained. Farmers may use non-crop residues such as thatch grass and reduce competition for crop residue use where farmers feed them to livestock during the dry season