Responses of total, reactive and dissolved phosphorus pools and crop yields to long-term fertilization

Maintaining an appropriate soil phosphorus level is key to ensure sustainable phosphorus management for crop production and to minimise phosphorus losses to water bodies. However, the effects of long-term fertilization on different soil phosphorus pools, crop yields and phosphorus loss risk remain unclear. This requires insights into the responses of soil phosphorus pools, crop phosphorus uptake with related crop yields and phosphorus loss to long-term phosphorus inputs. Changes in four soil phosphorus pools (P_CACL2, P_OLSEN, P_OX and P_TOTAL, respectively) and crop yield responses to various fertilization rates were examined in a 29-year long-term phosphorus fertilization experiment in China. Results showed that the increase in the four soil phosphorus pools was proportional to the accumulated phosphorus surplus, i.e., the input minus uptake. P_OLSEN and P_OX increased linearly with continuous phosphorus application and peaked at a phosphorus accumulation near 3200 kg P ha⁻¹. Beyond this threshold, continuous phosphorus application caused a gradual increase in P_TOTAL and a linear increase in P_CACL2, which implies an increasing risk for leaching. The P_OX pool accounted for 87% of the accumulated phosphorus surplus until soil phosphorus saturation occurred. The crop yields of wheat and maize responded clearly to changes in P_TOTAL, P_OX, P_OLSEN and P_CACL2, with P_OX explaining most of the yield variation. Furthermore, P_OX was highly correlated with P_CACL2, being a risk indicator for phosphorus leaching. Given that P_OX explains best how much of phosphorus surplus accumulates in soil, the variation in crop yield, and the risk for P leaching, it can be used as a valuable and reliable indicator to manage phosphorus sustainably.