The following section is a discussion of the importance of the problem of agricultural nonpoint source pollution, the conceptual framework and methods, and the research objectives of this study. Agricultural nonpoint source pollution is an important environmental concern. Agricultural nonpoint sources have been identified as the major contributors to sediments, nutrients, pathogenic bacteria, and pesticides affecting surface water quality (NRC, 1993). Severe soil degradation from erosion, compaction, or salinization, can damage the productive capacity of the soil and exacerbate water pollution. Sediments from eroded croplands interfere with the use of bodies of water for transportation; reduce the life of dams, locks, reservoirs, and other water developments; and degrade aquatic ecosystems. Nutrients accelerate the rate of eutrophication of lakes, streams, and estuaries; and nitrogen may cause health problems if ingested by humans in drinking water. Pesticides in drinking water, may become a human health concern and have been accused of disrupting reproduction of life in aquatic ecosystems (Overcash and Davidson, 1980). Statistics suggest that agriculture is the primary source of nonpoint pollution, affecting 64 percent of polluted U.S. rivers and 57 percent of impaired U.S. lakes (Figures 1-2). Nutrients (nitrogen and phosphorous) and sediments, the major types of pollutants closely associated with agricultural production, severely affect surface water quality in the United States (Figures 3-4) and loadings of these pollutants have increased in agricultural watersheds. These nutrients account for 13 percent of the destruction in U.S. rivers and 59 percent in U.S. lakes, making it the leading source of impairment in U.S. lakes (Smith et al., 1987).