Subsurface drainage loss of particles and phosphorus from field plot experiments and a tile-drained catchment

Movement of particles by water through the soil can be a significant pathway for P transport to surface waters in certain soil types. Our objective was to describe and quantify particulate matter (PM), particulate phosphorus (PP) and dissolved phosphorus (DP) transport to tile drains during controlled plot experiments. The results were compared to corresponding studies of natural storm events in the tile-drained catchment as a whole. Six rain simulations (irrigation 15.3-37 mm) were carried out at two 25 m2 plots on a loamy soil. Tracer chloride concentration in the drainage water peaked within 1 h of the onset of irrigation, thus indicating rapid macropore flow to the drains. PM, PP, and DP concentrations were highest in the initial drainage flow: 63 to 334 mg PM L-1, 0.177 to 0.876 mg PP L-1, and 0.042 to 0.103 mg DP L-1, respectively. Particulate matter and PP loss rates measured for the rapid drainage flow response were in the same range in the plot experiments as for nine precipitation events in the tile-drained catchment (13.3 ha): 171 to 630 g PM ha-1 mm-1 vs. 141 to 892 g PM ha-1 mm-1, and 0.57 to 1.75 g PP ha-1 mm-1 vs. 0.71 to 5.92 g PP ha-1 mm-1, respectively. Tracer analysis using 137Cs revealed that the PM in the drainage water was derived from the topsoil.