Availability of P for sugarcane plants was evaluated in a soil treated with organic composts rich in silicon. Five composts were formulated with following wastes: sugarcane bagasse, ashes of sugarcane bagasse, filter cake and castor bean plant residue enriched with silicon powdered rocks. The treatments consisted of five doses (0, 13, 26, 52 e 104 t ha-1) of each compost and an additional treatment with mineral fertilization (NPK). Soil samples were collected after the application of the treatments in order to carry out the following analyses: equilibrium P, "available"� Si, total organic C, and fractionation of the organic substances. The plant was sampled 150 days after planting for analysis of the leaf P. The application of composts made possible reduction of the adsorption of soil P, contributing to raise the absorption of this element by sugarcane crop; the reduction of the adsorption of P in the soil was atributed to Si from rocks of silicon, and the humic substances from composts and the compost containing ashes of sugarcane bagasse did not contribute to elevate content of "available"� Si in the soil.
"Available"� Si; humic substances; adsorption of P
