Potential use of phosphorus saturation degree as combined indicator for crop yield and leaching risks at regional scale

To ensure the sustainable use of phosphorus (P) fertilizers it is necessary to develop P management strategies that maximize crop yield while minimizing P leaching. Current P management practices, based on single agronomic soil P tests such as Olsen P (P_OLSEN), do not consider the P sorption capacity allowing one to predict soil P dynamics in response to long-term P inputs and related impacts on crop yield, P uptake and P loss. The oxalate extraction method, measuring contents of P, aluminium (Al) and iron (Fe), has been identified as a high-potential agri-environmental P test as it measures the reversibly sorbed P pool. This test gives insights in the plant-available P pool, the P sorption capacity and the degree of P Saturation (PSD). In this study, we evaluated the performance of P_OLSEN and PSD in explaining crop yield and P leaching risks, using long-term field experiments from China (n = 1) and Europe (n = 11), and we applied these insights to an inventory dataset (grid-sampling based) of Qiyang county in China. The variations in crop yield and P leaching risk were better explained by PSD (R²=0.5–0.95 for crop yield and 0.84–0.95 for P leaching risk) than by P_OLSEN (R²=0.68–0.93 for crop yield and < 0.73 for P leaching risk). The PSD target level to achieve 90 % of the potential yield was higher than the critical level to avoid enhanced P leaching for the Chinese but not for the European experiments. When applied on regional scale, we showed that the use of P_OLSEN might underestimate P demand for crop production and overestimate the potential leaching risk. Considering the theoretical advantages of PSD as a combined agri-environmental soil P test, we discussed the implications of its use for regional P management and showed that the α value, which is used to estimate PSD from oxalate extractable Al and Fe, needs to be adjusted for regional pedogenic and related climate factors.