Soil phosphorus dynamics during grassland establishment after deforestation and intensive agricultural use

The depletion of P resources is threatening agricultural sustainability and understanding the mechanisms by which land use change can restore soil health is therefore essential. This study investigated the long-term dynamics of soil phosphorus (P) following the conversion of cropland to grassland in northwestern Spain. The research evaluated how increases in soil organic matter (SOM) have influenced soil P forms along a 40-year chronosequence of grassland establishment, revealing a slow but gradual recovery of organic P (Po), mainly as P-monoesters and diesters. Intensive cropland management initially led to the significant loss of organic P through accelerated mineralization, promoting the dominance of inorganic P (Pi) forms. However, grassland establishment led to a gradual increase in the organic P contents, Po: Pi ratios and soil organic carbon (SOC): Po ratios, suggesting that conversion of cropland to grassland can partly mitigate the initial losses and promote P sustainability (improving nutritional P-use efficiency). Although the recovery of P levels and P distribution to the original state is a long-term prospect, the research findings highlight the important role of grassland conservation in sustaining soil nutrient cycles and fostering agroecosystem resilience.