The biological management of soil fertility project

Cover cropping, hedgerow intercropping, additional food-crop cropping and c ombinations of these with monocropping were studied as whole systems in S.E . Asia. The benefits of each system in terms of nutrient retention or suppl y, the sustainability of levels of organic matter and fertility were assess ed, along with the financial rewards or penalties and the constraints to ad option 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 f ood crop and provided enough marketable produce itself to increase a farmer 's income significantly. The residues also helped maintain levels of soil o rganic 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 a vailability 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 dec lined rapidly. Monocropping remains popular with farmers with little land o r without tenure, however. N-2-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 l east against it of the improved cropping systems investigated and probably stands the best chance of bring adopted by farmers in the region.