Philippe Vernier

Productivity of yam-based systems with herbaceous legumes and short fallows in the Guinea-Sudan transition zone of Benin

The principal driving force in agricultural research is to increase the yield of food crops. For farming to remain productive, it will be necessary to replenish the nutrients removed or lost from the soil. The objective of this study was to determine the impact of yam-based systems on soil productivity (dry matter production, nutrients recycled or removed, profitability and soil fertility changes). We compared smallholders’ traditional systems (1-year fallow of Andropogonon gayanus -yam rotation; maize-yam rotation) with yam-based systems with legumes (intercropped Aeschynomene histrix with maize-yam rotation; intercropped Mucuna pruriens with maize-yam rotation). The production of dry matter (tubers, shoots), nutrients removed or recycled, and soil properties were significantly improved on yam-based systems with legumes in comparison with traditional systems. Yearxa0×xa0Treatment interactions influenced significantly the tuber dry matter production. Sitexa0×xa0Treatment and Treatmentxa0×xa0Farmer interactions affected significantly nutrients removed or recycled. The amount of nutrients recycled or removed was dependent on the dry matter production that, in turn, depended on soil fertility, rainfall and farmers’ effect.Yam-based systems with legumes brought a higher present value than traditional systems in the first 4xa0years and appeared attractive for land, labour and cash productivities.

Dry Matter Production, Nutrient Cycled and Removed, and Soil Fertility Changes in Yam-Based Cropping Systems with Herbaceous Legumes in the Guinea-Sudan Zone of Benin

Traditional yam-based cropping systems (shifting cultivation, slash-and-burn, and short fallow) often result in deforestation and soil nutrient depletion. The objective of this study was to determine the impact of yam-based systems with herbaceous legumes on dry matter (DM) production (tubers, shoots), nutrients removed and recycled, and the soil fertility changes. We compared smallholders traditional systems (1-year fallow of Andropogon gayanus-yam rotation, maize-yam rotation) with yam-based systems integrated herbaceous legumes (Aeschynomene histrix/maize intercropping-yam rotation, Mucuna pruriens/maize intercropping-yam rotation). The experiment was conducted during the 2002 and 2004 cropping seasons with 32 farmers, eight in each site. For each of them, a randomized complete block design with four treatments and four replicates was carried out using a partial nested model with five factors: Year, Replicate, Farmer, Site, and Treatment. Analysis of variance (ANOVA) using the general linear model (GLM) procedure was applied to the dry matter (DM) production (tubers, shoots), nutrient contribution to the systems, and soil properties at depths 0–10 and 10–20 cm. DM removed and recycled, total N, P, and K recycled or removed, and soil chemical properties (SOM, N, P, K, and pH water) were significantly improved on yam-based systems with legumes in comparison with traditional systems.

Preservation of the environment on coral islands and intensification of agriculture: applied study on Maré, Loyalty Islands, New Caledonia

Elevated Pacific coral islands form a particularly vulnerable ecosystem characterized by fragile soils, usually in thin layers, and by the presence of a fresh water lens that replenishes itself only slowly and is also in balance with sea water. This lens often constitutes the sole supply of drinking water and any pollution affecting it would irremediably jeopardize this vital resource. In the Loyalty Islands, population growth combined with more intensive agricultural methods (use of fertilizers, pesticides, machinery, irrigation), often ill-suited to this type of environment, may cause irreversible damage. Agricultural research must, therefore, now try to obviate the dangers by developing techniques that will protect the environment while allowing essential economic development to proceed. Thus, in 1993, CIRAD New Caledonia, in collaboration with ORSTOM, initiated a new multidisciplinary research project in the Loyalty Islands to investigate problems relating to intensification and stabilization of agriculture on coral islands. The methods involve combinations of different levels of intensification (soil preparation × fertilization rates) and crop rotation. Methods are investigated in conjunction with the major food crops grown in the region (traditional tubers, vegetables), as well as fodder crops. Trials are also under way for monitoring infiltration (nitrates and pesticides). After two years of experiments, the first results have been obtained on crops (yield, labour input), and changes in soil fertility (mineral and organic contents) with an intensive method.