This document discusses using phosphate oxygen isotope ratios (δ18OP) to better understand phosphorus cycling in agricultural soils. The research aims to 1) identify the bioavailable fraction of phosphorus in soils and 2) identify phosphorus cycling impacted by fertilization and plant activities. It proposes developing δ18OP as a tracer to distinguish phosphorus sources and transformations. Key findings discussed include the transformation of applied fertilizer phosphorus into recalcitrant apatite pools in agricultural soils. The document concludes that stable isotope labeling and tracking allows in-depth understanding of phosphorus sources, transfers, and transformations in environments.