SUSPENDED-SOLIDS AND PHOSPHORUS LOADS FROM A CLAY SOIL .1. PLOT STUDIES

Phosphorus and suspended solids (SS) contents in tile discharge from two southwestern Ontario clay soil drainage experiments were measured over a 2-y period. For continuous corn plots, loads of SS and total P were 407 and 0. 88 kg ha** minus **1 y** minus **1, respectively. Suspended solids and total P loads from drains beneath permanent sod were 97 and 1. 85 kg ha** minus **1 y** minus **1, respectively. Comparison of these results with limited data on P and SS loads in surface runoff indicated that more than 50% of the total P load from these nearly level plots may be lost via subsurface tile flow. Overall, 34% of the total P load from subsurface drains was sediment-associated. Furthermore, crop cover, P fertilization rate, and tile drain depth were found to significantly affect dissolved P export.