Phosphorus Losses from Agricultural Soils to Surface Waters at a Small Agricultural Watershed in Korea.

Agriculture is considered an important nonpoint P source for both particulate and dissolved forms to surface waters. Dissolved P losses in runoff have been shown to be well related to soil P contents. Therefore, we investigated available P content in soil and dissolved reactive P concentration in surface runoff from a mixed land use (11.8% paddy field, 4.5% upland, 73.3% forest) 514 ha watershed in Goseong-Cheon, Gong-Ju, Korea. The importance of agricultural land use activities for supplying nutrients (N, P) to the Goseong-Cheon, Gong-Ju, Korea is examined and nutrient sources for a typical agricultural hill-land watershed within the Goseong-Cheon watershed are identified and assessed. As the loss of dissolved reactive P concentration in surface runoff (R²=0.87) has been shown to be related to soil test P (Lancaster P₂O₅) content, measures to minimize nonpoint source losses of agricultural P are most effective when implemented at the source. Also, it showed that the dissolved reactive P concentration in runoff water was highly related to the dissolved P concentration (R²=0.73). This suggests that near-stream surface runoff and soil P control P export from the watershed. Thus, the integration of areas of high soil P with areas of surface runoff production must be considered when guidelines are developed for P applications. Considering the distribution of high P soils alone may unnecessarily restrict farm management options without providing the desired reduction in P export from watersheds.