Technical Abstract: Based on up to 30 years of experimental and monitoring data, the outflow, N, and P exported from a typical agricultural hill-land watershed in Pennsylvania is examined in terms of critical source areas. Most of the surface runoff and P export occurs from areas near the stream. About 90% of the bioavailable P exported in outflow from this watershed was generated din storm flow from stream riparian zones. Annually, most of this export occurred during the largest 5-7 storms. In contrast, nearly all the exported nitrate originated as subsurface flow entering the soil or groundwater some distance from the stream, and is mostly exported in nonstorm flow. The observed NO3 export over the long term matches up very well with the N excess computed by N balance obtained by farmer survey for the contained agricultural land. By combining land use, hydrologic processes, watershed position, and N balance information for agricultural land, the major source areas for P and N are separate, predictable, and identifiable. We apply these ideas and techniques to our watershed and present the results as an example of this new approach.