ABSTRACT
Some 40 years ago, a number of agronomists around the world independently realized that the increases in the prices of synthetic fertilizers during the 1970s had produced a tremendous financial burden for smallholder farmers. Green manure/cover crops (GM/CCs) include a variety of plants, usually legumes, but also include trees, bushes, climbers, or creepers grown with, below, or between main-crop plants. The net costs of GM/CC systems vary greatly, depending especially on which GM/CC species are used and how many species are planted. The soil cover provided by most GM/CCs can be very important for conserving soil by curbing water erosion. GM/CCs can sequester significant amounts of atmospheric carbon in the soil through their growth of roots. Weeding and plowing are the heavy operations that have always given farmers with mechanized capability a major economic advantage.
