Phosphorus fractions and fate of phosphorus-33 in soils under plowing and no-tillage

Minimum tillage may alter soil P fractions through the application of P fer tilizers and the deposition of organic matter on the surface rather than be ing incorporated into the soil. This study was conducted to determine wheth er no-tillage (NT) systems affected soil organic and inorganic P fractions and the transformation of P from residues applied to soils. Surface soils ( 0-2 cm) under NT and conventional tillage (CT) were sampled from three long -term research sites. Inorganic and organic P was measured in the NaHCO3 mi crobial, NaOH, NaOH after sonication, HCl, and residual fractions extracted sequentially. Soybean (Glycine maw L.) residues labeled with P-33 were add ed to soils, incubated, and extracted periodically, and P-33 was counted in the different P fractions. Levels of (3)1P in NT were higher in some of th e fractions compared with CT; however, there was no consistency in P-31 fra ctionation across soil types due to tillage in any of the inorganic and org anic fractions. At the start of incubation, 56 to 82% of the applied P-33 w as extracted in the resin fraction in the three soils. Resin-P-33 followed a three-parameter single exponential decay model with a corresponding incre ase in other pools depending on soil. The increase in these pools followed a quadratic model in the three soils. By the end of the incubation period, the NaOH fraction accounted for the majority of the UP released from the la bile resin pool. An increase in the calcium phosphate pool occurred in the calcareous soil. Tillage had no effect on the fate of P-33 released from so ybean residues during the incubation period.