Nutrition loss through surface runoff from slope lands and its implications for agricultural management

Agricultural land use on slope areas is susceptible to nutrition loss via surface runoff, which would result in negative impacts on downstream waters. However, the linkage between nutrition loss and off-site crop production has been rarely reported. A study was conducted in a small independent agroforestry watershed in subtropical hilly terrain of China. Nutrition loss via surface runoff was measured from cropland, tea garden, citrus orchard, and natural woodland on a slope area. Grain production of rain-fed uplands and irrigated rice paddies were also investigated. Results exhibited that the runoff and associated nutrient loss were substantially affected by land use patterns. In general, the cropland generated the highest runoff and associated nutrient loss, followed by tea garden, citrus orchard, and woodland. Despite of land use patterns, the descending order of nutrient elements losses was: Ca2+ > K+ > SO4-S > TN (total nitrogen) > Mg2+ > TP (total phosphorus). Irrigated rice paddies had a higher level of self-sustainability of grain production compared with rain-fed uplands, which should be partially attributed to the nutrients input from irrigated water. The results imply that the runoff harvesting for irrigation, especially the runoff harvesting from agricultural land use patterns, can increase crop production with extra nutrition input by irrigation and reduce nutrition load to downstream waters.