The sustainability of cereal/legume intercropping was assessed by monitoring trends in grain yield, soil organic C (SOC) and soil extractable P (Olsen method) measured over 13 years at a long-term field trial on a P-deficient soil in semiarid Kenya. Goat manure was applied annually for 13 years at 0, 5 and 10 t ha -1 and trends in grain yield were not identifiable because of season-toseason variations. SOC and Olsen P increased for the first seven years of manure application and then remained constant. The residual effect of manure applied for four years only lasted another seven to eight years when assessed by yield, SOC and Olsen P. Mineral fertilizers provided the same annual rates of N and P as in 5 t ha -1 manure and initially ,gave the same yield as manure, declining after nine years to about 80%. Therefore, manure applications could be made intermittently and nutrient requirements topped-up with fertilizers. Grain yields for sorghum with continuous manure were described well by correlations with rainfall and manure input only, if data were excluded for seasons with over 500 mm rainfall. A comprehensive simulation model should correctly describe crop losses caused by excess water.
Conservation agriculture (CA) (zero tillage + organic inputs as surface residue) is believed to improve soil nutrient status, soil structure, control soil erosion, and also enhance soil fauna diversity. Despite the widespread interest in CA, empirical evidence of the benefits of CA on soil fauna diversity is limited, especially in low-input systems of sub-Saharan Africa (SSA). Consequently, the magnitude and effect by CA on soil fauna remains unquantified. The aim of this study was to evaluate the effect of CA and associated management practices on soil fauna richness and abundance. We hypothesized that CA and mixed cropping would positively influence soil fauna richness and abundance. We compared CA with conventional till (CT; with or without residues) in sole maize and maize-bean cropping systems. Soil macrofauna and mesofauna were sampled across the treatments in medium-term (6 years) trials in Embu, Central Kenya, and Kakamega (6 years) and a long-term trial in Nyabeda (15 years) using soil monoliths and core samplers, respectively. In agreement with our hypothesis, higher macrofauna taxonomic richness and mesofauna was recorded in CA than in CT without residues. This study demonstrated that: (1) medium to long-term addition of organic residues enhances soil fauna richness and abundance, (2) CA increases soil fauna taxonomic richness and abundance compared with CT, and (3) CA under maize-bean intercropping, rotation and sole maize cropping systems promote soil fauna richness and abundance compared with sole legume (common beans). We conclude that adoption of CA is important in enhancing richness of soil fauna. Given the numerous challenges faced by smallholder farmers of SSA in the adoption of CA, who in most cases rarely practice all the three CA principles simultaneously, we propose a further study that will determine the effects and interactions between each of the CA components on soil fauna richness and abundance.
Conservation agriculture (CA) is a promising technology for controlling soil degradation, mitigating drought, increasing crop yield and reducing production costs. We hypothesized that adopting CA system would improve system productivity and efficiency, hence resulting in higher profits. To test the hypothesis, we designed a study to evaluate water use efficiency (WUE) and the economic benefits (yield and gross margins) of CA in the upper and lower midlands agro-ecological zones of eastern Kenya. Four tillage treatments, including farmers' practice (residues removed), conventional tillage (residues removed) and two CA practices with residue retention (zero tillage and furrow-ridge), were laid out in 22 farmers' fields where each farm was treated as a replicate. The results are based on four consecutive seasons farmer-researcher managed trials during the period 2010 and 2012. CA significantly improved crop yields after the first season of experimentation. Joint use of zero tillage and furrow-ridge provided higher WUE and yield advantage (25-34%) in the third and fourth seasons compared to the conventional practices. The lower midlands zone gave higher WUE values, which can be explained by the effects of water harvesting and retention for longer period on CA treatments. CA practices have increased income on average by 12% resulted from labour cost reduction and yield increment. Weeding costs for conventional tillage were USD 88 ha −1 compared to USD 24 ha −1 for herbicide application under CA. Practicing CA will certainly increase crop yields, WUE, generate more revenue and diversify risks during poor seasons. However, these benefits may not necessarily be earned in the first season, but will accrue in subsequent seasons.
Climate change is any significant change in climatic conditions. Such changes may negatively affect productivity of the rain-fed agriculture practised by over 75% of the smallholder Kenyan farmers. The effect leads to failure to sustainably provide adequate food and revenue to famers. It is on this basis that an almost 8-year field study was conducted to evaluate and scale climate resilient agricultural technological options associated with Conservation Agriculture (CA) systems and practices (no-till; maintenance of permanent soil cover; and crop diversification - rotations and associations), complemented with good agricultural strategies. The activities involved were targeted to sustainably increase productivity of maize-legumes farming systems while reducing environmental risks. The results showed improved soil properties (physical, chemical and health) and consequently increased crop yields and human nutrition by over 30%. Such benefits were attributed to cost savings arising from NT and reduced labour requirement for weed control. This was further based on enhanced crop soil moisture and nutrients availability and use efficiency leading to over 25% yield increase advantage. Apart from the field trials, the study used the Agricultural Production Simulator (APSIM) computer model to simulate CA scenario with the aim of providing potential quick answers to adopting CA practices for farm system productivity. The results were inclusively shared, leading to over 21% increase in the number of farmers adopting the CA practices within and beyond the project sites. The study's overall recommendation affirmed the need to integrate the CA practices into Kenyan farming systems for sustainable agricultural livelihoods and economic opportunities.
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