Nutrient Management Planning Effects on Runoff Losses of Phosphorus and Nitrogen
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Non-point source pollution accounts for a large proportion of surface and ground water contamination. The objective of this study was to evaluate the differences in losses from commonly-used best nutrient management practices (BMPs) involving incorporation of manures and fertilizers on an Appalachian and a Coastal Plain soil. Poultry litter and dairy manure were applied in consecutive study years on 4.6m (15ft) x 15.2m (50ft) (Appalachian site) and a 6.1m (20ft) x 15.2m (50ft) (Coastal Plain site) field plots in no-till or conventional-till corn production. The manures were incorporated into the soil for one-half of the plots and a 30-minute, 76-mm simulated rainfall event (consistent with a 2-yr. storm event) was applied to all plots after planting and harvest, . Runoff samples, taken every five minutes, were analyzed for soluble phosphorus (SP), total phosphorus (TP) and sediment-associated particulate phosphorus (PP), nitrate, ammonium, and total nitrogen (TN), then converted to kg ha-1 load. Observed SP loads were significantly greater at the coarser textured Coastal plain site. There were minimal differences in TP losses between spring and fall simulations for both manures. P loads in runoff were significantly higher in plots that did not receive incorporation of either manure. Observed SP losses were greater from dairy manure than poultry litter treated soils. SP contributions to TP from poultry litter were much smaller than dairy manure and PP played a larger role in poultry litter TP load. Post-plant runoff volume was controlled by reduced tillage in poultry litter plots and residue cover in dairy manure plots. Sediment, nitrate, ammonium and organic nitrogen (N) loss was controlled by tillage in both years. . However, this may be offset by the observed increase in leaching of N. Post-harvest nutrient losses were less than post-plant losses from both manures, but to a lesser degree with dairy manure suggesting that, especially with wet manures, maximizing the time between application and a runoff event is critical in minimizing pollution risk to surface water.