Phosphorus pools responses to land-use change for sugarcane expansion in weathered Brazilian soils

Abstract

Without proper management, land-use change (LUC) associated with producing sugarcane (Saccharum officinarum) for bioenergy in Brazil can lead to soil degradation and have negative implications on ecosystem functions. Phosphorus (P) depletion is one of the most frequent causes of land degradation in tropical environments, and as such, soil P pools have been identified as potential indicators of negative environmental impacts. We quantified soil P dynamics for the most common LUC sequence in sugarcane expansion areas [i.e., native vegetation (NV) to pasture (PA) to sugarcane (SC)], to determine if and how these changes could be used to evaluate environmental impacts of LUC in weathered Brazilian soils. Soil samples were collected from three areas in central-southern Brazil, representing the primary sugarcane-producing region of the world. Soil P fractionation was performed, and P stocks were calculated for the surface 30cm. Soil chemical attributes and macrofauna data were correlated with P pools. Long-term conversions from natural ecosystems (Cerrado and Atlantic forest biome) to extensive PA decreased total P stocks by 31.2% indicating progressive soil degradation in these areas. In contrast, the LUC from PA to SC increased total P stocks by 35.6%; nevertheless, fertilization management altered the soil P-cycle, causing P accumulation in less plant-available forms. Available P increases to support adequate SC growth are still needed. Applying P using organic residues increased labile organic P and may be a complementary strategy for increasing nutrient supplies in SC fields. Phosphorus availability showed significant positive correlations with other soil chemical properties and clay content, while the functional diversity of soil macrofauna was strongly correlated with labile and biological P. We conclude that P pools can be useful indicators for assessing LUC modifications on soil quality in the tropics, and recommend they be used to assess land degradation and environmental sustainability within SC expansion areas in Brazil.