26th Southern Conservation Tillage Conference TILLAGE AND N-FERTILIZER SOURCE EFFECTS ON YIELD AND WATER QUALITY IN A CORN-RYE CROPPING SYSTEM

Tillage and nutrient source choices have important agronomic and environmental consequences in cropping system management, which need to be quantified in the Southeast. In three years of research at the USDA-ARS J. Phil Campbell Sr. Natural Resource Conservation Center, Watkinsville-GA, we compared agronomic benefits and water quality impacts of no-till and poultry litter versus conventional-till and conventional fertilizer in a corn-rye cropping system. No-till and poultry litter each enhanced corn yield by 15 to 23% over three years. When combined, they enhanced yield by 27%. Off-site effects in terms of nitrate-nitrogen and ammonium-nitrogen losses through runoff or drainage were similar among treatments. Concentrations were dependant on N application rates. Below a 3 ton acre-1 application rate of poultry litter (90 lbs N acre-1), nitrate levels are expected to be below 10 ppm, especially if the first precipitation or irrigation event is delayed after N application. Application of poultry litter increased loss of ortho-phosphate in runoff by 5 to 6 times compared to conventional fertilizer. The sex hormones estradiol and testosterone coming off poultry litter plots were not above levels observed for conventional fertilizer plots. Managing corn with no-till and/or poultry litter at normal N application rates has agronomic advantages, and does not appear to present large additional risks of nitrate or hormone contamination of water resources. However, offsite effect of ortho-phosphate is a concern