Temporal and spatial variations of phosphorus losses and drainage in a structured clay soil

Drainage discharge and loss of dissolved (PO4-P) and particulate (part-P) P from four artificially drained plots with clay soils were studied over a four-year period. The loads of total P observed during this time ranged from 421 g P ha−1 to 805 g P ha−1. Annual losses and losses during high-flow events were measured. Leaching of P occurred episodically with the largest losses during high-flow events. Concentrations of PO4-P during high-flow events were positively related to discharge rates and the curves obtained were grouped into two classes based on similar slopes within the class. Concentrations of part-P were related to concentrations of suspended soil material, and increased with increasing discharge rate, but the slope of the curves obtained varied over a wide range. High P concentrations were observed in high-flow episodes which occurred after P fertilizer applications.