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 pathwa y for P transport to surface waters in certain soil types. Our objective wa s to describe and quantify particulate matter (PM), particulate phosphorus (PP) and dissolved phosphorus (DP) transport to tile drains during controll ed plot experiments. The results were compared to corresponding studies of natural storm events in the tile-drained catchment as a whole. Six rain sim ulations (irrigation 15.3-37 mm) were carried out at two 25 m(2) plots on a loamy soil, Tracer chloride concentration in the drainage water peaked wit hin 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 drai nage flow: 63 to 334 mg PM L-1, 0.177 to 0.876 mg PP L-1, and 0.042 to 0.10 3 mg DP L-1, respectively. Particulate matter and PP loss rates measured fo r the rapid drainage flow response were in the same range in the plot exper iments 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), respec tively. Tracer analysis using Cs-137 revealed that the PM in the drainage w ater was derived from the topsoil.