Changes in soil phosphorus pool induced by pastureland intensification and diversification in Brazil

The adoption of more intensive and diversified pasture systems is a promising alternative to improve sustainability of grazing lands in Brazil. Phosphorus (P) is one of the main determinants of ecosystem function in these management systems; therefore, we assessed the effects of adopting more intensive and diversified pasture management systems on soil P dynamics in a set of field experiments. Treatments included fertilized pasture (FP), integrated crop-livestock (ICL), integrated livestock-forest (ILF), compared to conventional management systems (CS) under contrasting climatic conditions (tropical humid, tropical mesic and subtropical). P fractions and total P were determined by soil layer to 1 m depth. Size and distribution of P stocks were related to soil organic matter (SOM) fractions and to clay type and content. Based on the results, P biological fraction represented 9% of P in the soil, on average, in CS under the three assessed climatic conditions. Management systems with FP and the ones with ICL and ILF mainly influenced labile (0.01, 0.02 and 0.03 Mg ha^-1 yr^-1, respectively), moderately labile (0.03, 0.01 and 0.07 Mg ha^-1 yr^-1, respectively) and total soil P fractions (0.21, 0.08 and 0.20 Mg ha^-1 yr^-1, respectively). Clay content and pH were the soil properties mostly related to P fractions; besides, P fractions presented close relationship with these fractions and with total soil C and N, as well as with different SOM fractions. These results can be the scientific basis for governmental initiatives focused on recovering degraded pasture sites in Brazil. The establishment of management practices that favor efficient P use are essential to improve the sustainability of production systems.