Land use and altitude: how do they influence the phosphorus fractions?

Soil use and management systems modify phosphorus (P) dynamics by changing the different P compartments. However, the interaction between land-use change and altitude is not clear. This study aimed to evaluate the effect of land use on P forms in different soil aggregate classes of Ultisols located at two altitudes. Soil samples were collected in four land-use systems (agroforestry system, secondary forest, pasture, and eucalyptus) located at two altitudes in the Atlantic Forest biome, Brazil. Phosphorus fractions were assessed using sequential fractionation. In general, recalcitrant forms represented about 70% in the agroforestry system, 66% in the eucalyptus, 65% in the pasture, and 57% in the secondary forest relative to the total P content of all land uses at both altitudes. The soil aggregate classes of smaller diameter presented higher P contents in all fractions. The smallest soil aggregate classes showed up to 65% more P than the classes with smaller diameters in the different land-use systems and altitudes.