Constraints of Soil Conservation Innovations in Yam-based Systems with Herbaceous Legumes in the Guinea-Sudan Transition Zone of Benin Republic

In Benin nowadays, farmers hardly have the possibility to rely on long duration fallow and yam is being cultivated in 1 or 2-year herbaceous fallow-yam or maize-yam rotation systems with manual incorporation of residue into the soil. One of the most serious problems of farming systems in West Africa is the excessive reduction of agricultural productivity related to the “slash and burn” and shifting cultivation systems. 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). Herbaceous legumes (Mucuna in particular) used for yam production were appreciated by end-users for their capacity to restore soil fertility, maintain soil humidity and control weeds (Imperata cylindrica in particular) as well as in low and relatively high population zones. This study was carried out in 2005 in the Guinea-Sudan transition zone of Benin in a low (Savalou, Bantè, Savè and Ouessè) and in a relatively high population density zone (Dassa-Zoumè, Glazoué). This study examines end-users in the framework of focus group and individual surveys in 306 farm households, constraints degree of severity of yam-based cropping systems and participatory solutions in order to improve policy transacting in rural areas for sustainable yam production. The results showed a significantly high constraint degree of severity for herbaceous legume biomass incorporation (52% and 46%) for Mucuna and Aeschynomene respectively during individual surveys and 82% during focus groups for both legumes. Crop competitions, field access (with Mucuna), animal divagation, fertilizer cost, biomass burn, seed consumption, market and grains harvest (with Aeschynomene) were additional constraints as well as in low and relatively high population density zones. On the seed production plot, the biomass of Aeschynomene at senescence could be shaken within basins to collect easily the seeds and avoid loss. The mixture of Aeschynomene seeds with dry sand (3/4 sand - 1/4 seeds) solves the problem of planting small seeds. Before the legumes reach physiological maturity, three-quarters of biomass could be manually incorporated into the soil before the dry season during ridging and the remaining biomass could be left on the surface as mulch in order to reduce the workload related to the biomass incorporation into the soil. The practice of a firewall and fire of reference around the plot is necessary to avoid the burning of the mulch in the dry period. Mucuna seeds valorisation occurred to generate additional income for smallholder households. Animal nutrition with Mucuna grains deserves to be more investigated. The crop-livestock integration with these herbaceous should be an opportunity for yam production because of agro-pastoral potential in the Guinea Sudan transition zone of Benin. Integration of forage legumes into traditional fallow management can help improve both forage supply at a time of feed scarcity and soil fertility.