Phosphate fixation capacity of eight soils representative of the Piracicaba municipality, State of Sao Paulo, Brazil, were studied. Representative samples of the following soils were utilized: Iracema, Luiz de Queiroz, Pau D'Alho, Monte Olimpo, Lageadinho, Quebra Dente, Gibóia e Ribeirão Claro. Once the amount of phosphate fixed by each soil was known, the quantity of P to be added to neutralize their respective fixing capacities was calculated. The available P from soils incubated without this element was extracted and a calculation was made to verify how much of it must be added to the soils for them to maintain their mean values of available phosphorus. Mean values of available P, soluble phosphate that must be added to the soils varied according to soil type. It was concluded that the percentage of clay is a good index to evaluate the capacity of phosphate retention by soils from the municipality of Piracicaba.
phosphate fixation; phosphate adsorption; available phosphorus