Changes in soil P-fractions by the addition of phosphoric rock at different incubation times and moisture contents

Abstract

The objective of this study was to compare the dissolution of the phosphate rock (PR) Monte Fresco in two acidic soils very contrasting in physicochemical characteristics, through a scheme of fractionation at different periods of incubation and moisture contents. Iguana, a very sandy soil with a low natural fertility and low phosphate retention; and much more acid Bramón soil with a higher exchangeable Al content but with greater natural fertility and high capacity of phosphate retention. Iguana soil dissolved the PR in a greater proportion than the soil Bramón, since this soil, despite its strong acidity presented high levels of P (total and available) and exchangeable Ca which generated less appropriate conditions for the reaction of the PR. During incubation with PR, as a result of the redistribution of the major fractions of P (P-HCl and P-residual) originally present in the PR, occurred a significant increase for the P-resin and microbial-P fractions in Iguana soil; and in P-resin, microbial-P, NaOH-Pi and Po for Bramón soil, in this case, possibly associated with its higher C content. Higher moisture contents decreased more labile P-fractions (resin and NaHCO₃) values in both soils, which implies, a higher adsorption of P due to a greater contact between the adsorbent surfaces and newly released P from the PR.