Excess sediment, phosphorus(P) and/or nitrogen (N) impair most Iowa lakes and many streams. Most of the sediment and nutrients originate from agricultural fields or stream banks. Previous research on P loss with surface runoff in the Northwest Iowa region was based on short-term rainfall simulations and included a limited set of conditions. The rainfall simulations provided useful information about potential differences between management practices but could not measure long-term differences or annual sediment and P loads. Very limited work has been conducted elsewhere in Iowa to study P loss with runoff based on natural rainfall and large-scale plots.