following the construction of the hydroelectric power station of solteira island in the late 1960s, some areas were deforested and used as "lending areas". the soil was extracted from these areas, which acquired chemical and biological characteristics far from the ideal. this work aimed to evaluate the use of organic residues as a reconditioner of degraded subsoil and quantify its effects on soil microbial activity and fertility in 'barbatim？o' (stryphnodendron polyphyllum mart.) cultivation. the area is located at the unesp/ ilha solteira campus farm, in selvíria - ms. four sections (repetitions) of 250 m2 (10 x 25 m) were allocated, with 10 treatments for each, as follows: control; liming; fertilizing+n+p; liming+n+p; n+p+water hyacinth; n+p+sugar cane bagasse; n+p+water hyacinth+sugar cane bagasse; liming+n+p+water hyacinth; liming+n+p+sugar cane bagasse and liming+n+p+water hyacinth+sugar cane bagasse. the chemical characteristics of the subsoil were evaluated as well as plant growth, carbon microbial biomass (cmb) and released c-co2 , metabolic quotient (qco2) and microbial quotient (qmic), in 5 subsoil sample collecting times (june, august, november and december, 2005 and march, 2006). the subsoil displayed the same acid and poor nutrient level characteristics after a year. during the experiment, the cmb presented stabilization tendencies and the qco2 and qmic decreased in the same period. in all, even below the ideal level, the organic residues showed better results, with small positive differences for water hyacinth. cmb exhibited seasonal variations.