The biological management of soil fertility project

Abstract

Cover cropping, hedgerow intercropping, additional food-crop cropping and combinations of these with monocropping were studied as whole systems in SE Asia. The benefits of each system in terms of nutrient retention or supply, the sustainability of levels of organic matter and fertility were assessed, along with the financial rewards or penalties and the constraints to adoption of each cropping system in terms of extra labour, conflicts with off-farm labour and farmers' attitudes. Leguminous pre- and post-crops such as groundnut increased the yield of a food crop and provided enough marketable produce itself to increase a farmer's income significantly. The residues also helped maintain levels of soil organic carbon and nitrogen in soil. Analysis suggested a good price for the secondary crop to be key, however, as is sufficient water to grow it and availability of or tenure on the land for a farmer to be willing to invest. Hedgerow intercropping boosted soil fertility but did not increase incomes sufficiently, monocropping was profitable but yields and soil fertility declined rapidly. Monocropping remains popular with farmers with little land or without tenure, however. Nitrogen fixation was sufficient to match offtake in a moderately yielding food-crop in these systems; more intensive production requires additional input. Overall leguminous secondary cropping has the least against it of the improved cropping systems investigated and probably stands the best chance of being adopted by farmers in the region.