The characterization of several soil phosphorus (P) pools allowed the evaluation of P components not usually monitored in fertilizer soil tests and can help to understand this nutrient's cycle. The aim of this study was to evaluate the changes in P pools of a Fluventic Eutrochrepts fine clay which had been under long-time sugarcane plantation. In one situation the sugarcane had been cropped for 55 years with and without trash burning prior to harvesting. The other sugarcane plantation, cultivated for 35 years, with crop residues and leaves burning, had received annual stillage inputs through aspersion irrigation at rates of 120 m³ ha-1 yr-1. Soil samples were taken from the 0-0.20 and 0.20-0.40 m layers and a sequential P fractionation method was performed. Total P, available P, organic P, inorganic P and P in humic substances were also evaluated. The results of this study indicated that the management with trash preservation on the soil surface promoted higher P content in all evaluated pools. The preservation of crop residues and leaves and stillage addition modified the P pool distribution, promoting a decrease of non-labile pools and consequently an increase of labile pools. At all studied sites the P content was higher in the humic than in the fulvic acid fraction. The smallest relative participation of organic pools at the site without burning suggests the contribution of this pool to the available P through its mineralization.
sequential fractionation; organic phosphorus; availability
