Three fertilizer experiments, designed to study mainly the effect of under-sowing the corn crop with velvet beans (Stizolabium sp.), were conducted for several years on different soil types of the State of São Paulo. After the last harvest, composite soil samples were taken from the differently treated plots and analysed. While the limestone as well as the phosphorus and potassium applications increased considerably the concentrations of the nutrients they contain, the under-sowing of velvet beans, although increasing the following corn yields, did not increase the organic matter content of the mentioned soils nor did it practically change the other chemical soil characteristics studied.