Phosphorus release risk on a calcareous purple soil in southwest China

Growing concerns about water eutrophication male it imperative to control phosphorus (P) losses from agricultural soil to water. A Quantity-Intensity (Q-I) relationship that reflects the potential of soil P release to water was developed on the calcareous purple soil in southwestern China. Results showed that a change point appeared at 30 mg kg(-1) for Olsen-P and 22 mg kg(-1) for iron-oxide impregnated strips extracted P (FeO-P), respectively, on the curve of CaCl2-P against soil test P (STP). Above the change point, the P release was much more rapid with the increase of STP. Therefore, a threshold in STP was derived to support P source management practices on the soil.