Nutrient Management Planning Effects On Runoff Losses of Phosphorus and Nitrogen.

The management of nutrients in agricultural production systems and the resultant non-point source pollution accounts for a large proportion of the contaminants affecting surface and ground waters. To estimate phosphorus and nitrogen losses from agricultural land, models such as the Chesapeake Bay Watershed Model need accurate nutrient loss efficiencies for various best management practices. The objectives of this study were to (1) determine the nutrient loss of some best management practices commonly recommended in nutrient management planning; (2) evaluate the differences in phosphorus and nitrogen runoff losses resulting from the use of organic sources versus commercial fertilizer; and (3) determine the impacts of incorporation and manure type on phosphorus and nitrogen losses. Three replications of small scale field plots (e.g. 20 x 50 ft) were established at a Coastal Plain and Appalachian location in a randomized complete block design. Animal wastes and commercial fertilizer were applied according to nutrient management planning recommendations for corn (Zea maize spp.) crop production. Poultry litter was the waste nutrient source for one set of plots during the first year of the study and dairy manure was the waste nutrient source for another set of plots during the second year of the study. Nutrients were applied to specified plots at rates equivalent to nitrogen-based plans, chemical fertilizer plans, and phosphorus removal plans. The effects of soil incorporation were evaluated by tilling one-half of the plots immediately after animal waste and chemical fertilizer application. Runoff and sediment loss as well as nutrient losses in runoff were determined in the spring and fall by applying simulated rainfall. A 30-minute, 76-mm simulated rainfall event was applied to all plots after planting and after harvest using a variable intensity rainfall simulator. Runoff samples were continuously collected at 5-minute intervals during the 30-minute rain events. Nutrient losses for different nutrient management practices were evaluated by analyzing filtered and unfiltered runoff samples for ammonium (NH4-N), nitrate (NO3-N), phosphate (PO4-P), total nitrogen (TN), and total phosphorous (TP). Leached nutrients were determined from soil samples collected to a 105-cm soil depth taken prior to nutrient application and following crop harvest. Statistical analyses will be performed to determine the effects of nutrient management planning on runoff, sediment loss, and nutrient losses.