Cultivation affected the level of inorganic phosphorus more than the organic pool of the Pampas soils in Argentina

Abstract

The effects of land use on soil organic and inorganic phosphorus (P) stockswere assessed in the Pampas. Three hundred and eighty-six paired siteswidely distributed over an area of ca. 50 Mha were sampled. Land usetypesincluded soils under trees, uncropped soils, cropped soils at the pasturephase of a mixed rotation, cropped soils at the crop phase of a mixed rotation,and flooded soils. Slight differences in organic P stocks were found amongland uses. Organic P was 21?35% lower in flooded soil than in the othertreatments in the 0?100 cm depth. Inorganic P was significantly lower (ca.27%) in pasture and cropped soilsthan in the uncropped controls at 0?25 cmdepth. The ratios of organic P/inorganic P and organic C/organic P decreasedwith depth and did not significantly differ among the sites. The influence ofcultivation on inorganic P to a depth of 100 cm depended on the initialphosphorus content of the soil. Soils rich in phosphorus lost substantialamounts of their phosphorus stocks, in some cases losses were as high as70%, whereas phosphorus-poor soils presented only small changes in theirinorganic P levels.