Suspended Solids and Phosphorus Loads from a Clay Soil: I. 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 (Zea mays L.) plots, loads of SS and total P were 407 and 0.88 kg ha−1 y−1, respectively. Suspended solids and total P loads from drains beneath permanent sod were 97 and 1.85 kg ha−1 y−1, respectively. Comparison of these results with limited data on P and SS loads in surface runoff indicated that >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. Dissolved P concentrations in effluent from permanent bluegrass sod exceeded those from continuous corn and rotational plots. Subsurface sediment and sediment‐associated P loads were highest from continuous corn. Greater soil cover over the tile line decreased both sediment and P concentrations. Sediment‐associated P concentrations increased with P fertilization rate at one of the experimental locations.