Summary |
Many studies have shown the effects of agricultural practices on the amount of nutrient runoff from cropland. Few studies, however, have examined the importance of intrinsic land properties. The purpose of this study was to determine the relative importance of intrinsic land properties and agricultural practices in generating edge-of-field nutrient loadings. A secondary purpose was to identify nutrient reduction strategies for primary agricultural soils within the study area. The study area this research was the Jerry's Creek Watershed in eastern North Carolina. Research methodology used involved; (1) the collection of 22 input parameters for 534 ten acre parcels of land within the study area; (2) using the Agricultural Non-point Source Pollution Model (AGNPS) to simulate nitrogen and phosphorus losses from each of the ten acre parcels; (3) statistically analyzing the relative effect of each of the 22 input parameters on nitrogen and phosphorus losses with stepwise multiple regression and stepwise multiple regression with principal component scores; and (4) analyzing the data generated by simulations and statistics. Results indicate that agricultural management variables have a much greater effect on both sediment and soluble phase nutrient losses from cropland that do intrinsic land properties. Management related variables, however, were less dominant with respect to soluble phase nutrient losses. Management variables affecting land surface characteristics the "C" factor (Universal Soil Loss Equation), Manning's Roughness Coefficient, and surface condition constant had the greatest effect on sediment phase losses. Fertilization level had a dominant effect on soluble phase losses. Simulation results indicate that tobacco has the greatest total nutrient losses from each soil series in the study area. Corn generally had the lowest total nutrient losses from well drained soils while soybeans or peanuts had the lowest losses from poorly drained soils. Results indicate that best management practices (BMPs) can effectively reduce nutrient losses from cropland; especially sediment phase losses. Tillage and management practices that reduce or slow surface runoff were generally the most effective means of reducing sediment phase losses. Tobacco had the greatest losses from all soil series within the study area and therefore, should receive priority with respect to either BMPs or land-use changes. The Coxville, Gritney, and Roanoke soil series had much higher total nutrient losses and lower crop yields than most of the other agricultural soils within the watershed. These soils should receive prioritization for retirement from crop use. |