Excess sediment, phosphorus (P) and/or nitrogen (N) impair many Iowa lakes and streams. Most of the sediment and P originate from fields and stream banks. Previous research was based on rainfall simulations. This technique provided useful information about potential differences between management practices, but estimated poorly long-term differences and total losses. Little work has been conducted elsewhere in Iowa to study P loss with surface runoff based on natural rainfall and large-scale plots. Therefore, a long-term study was established to investigate effects of corn and soybean production, tillage, and fertilizer or manure P management system on crop yield and loss of soil and P with runoff.