Daroub, S., F. J. Pierce, and B. G. Ellis. 2000. Phosphorus fractions and fate of phosphorus-33 in soils managed under plowing and no-tillage. Soil Science Society of America Journal 64:170-176.
Minimum tillage may alter soil P fractions through the application of P fertilizers and the deposition of organic matter on the surface rather than being incorporated into the soil. This study was conducted to determine whether 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, microbial, NaOH, NaOH after sonication, HCl, and residual fractions extracted sequentially. Soybean (Glycine max L.) residues labeled with 33P were added to soils, incubated, and extracted periodically, and 33P was counted in the different P fractions. Levels of 31P in NT were higher in some of the fractions compared with CT; however, there was no consistency in 31P fractionation across soil types due to tillage in any of the inorganic and organic fractions. At the start of incubation, 56 to 82% of the applied 33P was extracted in the resin fraction in the three soils. Resin-33P followed a three-parameter single exponential decay model with a corresponding increase 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 33P released from the labile resin pool. An increase in the calcium phosphate pool occurred in the calcareous soil. Tillage had no effect on the fate of 33P released from soybean residues during the incubation period.
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