Using Long-Term Evaluations of Arkansas Cropping Systems to Reduce Nitrate Leaching and N2O Emissions.

There have been reports in the literature that nitrogen leaching losses from the Mississippi River Basin cropping systems are contributing to the transport of nitrogen loads to the Gulf of Mexico and to the resulting hypoxia problem in this area. The Arkansas Delta region has been identified as a potential source of the nitrogen entering the Mississippi River. To assess the effects of cropping systems and management practices on the potential leaching losses from agricultural fields located in the Arkansas Delta, we used the new Nitrogen Loss and Environmental Assessment Package with GIS Capabilities (NLEAP-GIS 4.2) that was released in 2010 to conduct a preliminary long-term analysis of a series of management scenarios for crops growing under hydrological type A and D soils. Average state yield production and recommended N inputs were used for these scenarios. Simulations were conducted for no-till and conventional systems; for each of these systems, we evaluated corn-corn and corn-soybean rotations. Factorial analyses of spring vs. fall applications, surface application vs. incorporation of N, best N rates, and 75% over-application were conducted. The analyses showed that rotations of soybeans into corn systems reduced the emissions of N₂O across the Arkansas Delta and reduced the NO₃-N leaching losses as well and suggest that use of best management practices and realistic N application rates can significantly contribute to decreased losses of reactive N to the environment. These analyses further suggest that NLEAP-GIS 4.2 is an effective tool for evaluating agricultural management practices.