Moderately Resistant Phosphorus Forms In Subtropical Ultisol Of Argentina

The efficiency of phosphorus (P) fertilization may be improved through knowledge of soil P fraction changes with time. This study examined: i) the distribution of P fractions according to Hedley's fractionation scheme and ii) the sequential changes in soil organic P (OP) and inorganic P tip) in a typical Kandihumult,under favorable conditions for mineralization and under depletion conditions, with and without P fertilization. Soil P fractions considered were IP-resin, IP- and OP-bicarbonate, and IP- and OP-hydroxide. The soil is characterized by the predominance of moderately resistant P, in organic and inorganic fractions. In the presence of favorable conditions for mineralization, a substantial decrease in moderately resistant organic P was observed, enhanced even more by fertilizer incorporation. The decrease of total extracted P (TPe) before depletion situations was mainly produced in the moderately resistant fraction, that registered a decrease of 23% (of this value 65% were due to OF). The main fate of the fertilization, in both situations (active mineralization as well as depletion) was moderately resistant inorganic phosphate.