The aim of this work was to study the influence of residues of five Sorghum bicolor L. (cv CMS XS 376, CMS XS 365, BR 304, BR 700 and CMS XS 755) on soybean growth. These residues were harvested in three different stages during the sorghum cycle (blooming, milking and physiological maturity) and either spread on the soil surface or totally incorporated in soil, in the proportion of 4 g kg-1 of dry matter in the soil (a Dark Red Oxisol under cerrado vegetation). In the plant treatments, three soybean plants (cv. Doko) were grown in pots with 3 kg of soil up to the blooming stage. In the no-plant treatments, the soil was periodically sampled for N (NO3, NH4) forms. The shoots of soybean plants were collected from each treatment, for total N absorption. Afterwards, samples were taken to determine the variation of available N extractable with KCl 2 mol L-1. The main results showed a negative influence of cultural residues on soybean development, N absorption, nodule weight, and microbial biomass. These effects were dependent on sorghum material and residue management. Carbon immobilized by the soil microbial biomass was higher when the sorghum residues were distributed on the soil surface.
Nitrogen; mineralization; nutrient availability; Sorghum bicolor L