Yam-Based Cropping Systems Performances with Herbaceous Legumes and Chemical Fertilizers

In West Africa, the traditional yam-based cropping systems (shifting cultivation and slash-and-burn) contribute to the deforestation, land degradation and low soil productivity. With the aim of designing more sustainable yam cropping systems, the agronomic research organization in Benin implemented alternative systems including herbaceous legumes (Aeschynomene histrix and Mucuna pruriens var utilis) and chemical fertilizers.This study examines the effect of rotations with herbaceous legumes and chemical fertilizers on yam yields and soils, to see how consistent they are for the different farmers within a site, and different sites. A perennial experiment was implemented for 4 years, with 2-year rotations, smallholder farmers’ traditional rotations maize-yam or 1-year Andropogonon gayanus (natural fallow)–yam, with rotations intercropped Aeschynomene histrix with maize-yam or intercropped Mucuna pruriens with maize and chemical fertilizers. The experiment was conducted with 32 farmers, eight in each site (Miniffi, Gomè, Akpéro and Gbanlin). For each of them, we used a randomized block design with four replicates and four crop rotation treatments. The same treatments didn’t “work” for all 32 farmers from one year to another. The effects of treatments on yam yields differed significantly for the different farmers within a site, and different sites. Yam has a poor response to mineral fertilizer applications. When natural fallow and maize as precedents were compared, yam yield was higher after a (short) natural fallow, despite the chemical fertilizers supply on maize. Indeed, the decrease in yam yields was slower year after year after fertilized maize compared to natural fallow but yam yields remained the lowest after maize. Soil nitrogen and phosphorus concentrations were improved on different sites on yam-based cropping systems with herbaceous legumes and chemical fertilizers in 0-10cm and 10-20cm depth.

Keywords: Chemical fertilizers; Herbaceous legumes; Production; Soil fertility; Sustainable agriculture