Assessment of Nitrogen Management and Cropping Systems in the Arkansas Delta Irrigation Systems.

It has been reported that nitrogen that is lost into the Arkansas Delta can be transported to the Mississippi River Basin, potentially contributing to the nitrate load to which the hypoxia problem in the Gulf of Mexico has been attributed. Developing effective methods of reducing these nitrogen losses requires the development and validation of new tools that can be used to conduct quick assessments of how management practices may affect nitrogen losses. Field studies were conducted in 2008 and 2009 to collect data to test the new NLEAP-GIS 4.2 model and its capability to simulate nitrogen dynamics for different cropping systems grown at Arkansas State University and at the Judd Hill Plantation, an environmentally sustainable farm. The first NLEAP-GIS 4.2 simulation  for this region, which analyzed  cotton, soybean and corn grown in the Arkansas Delta, showed that the model was able to accurately simulate nitrogen dynamics and the effects of management on residual soil nitrate (P < 0.01). The model indicated that nitrate leaching and N₂O emissions from soybean and cotton systems are lower than those from corn systems. Model simulations also showed that the residual nitrate can range from 30 to 200 lbs NO₃-N in the top 1.5 m of soil, in agreement with measured values. The simulated values indicate a need to improve management practices and that rotations of soybeans and cotton with corn could play an important role in reducing nitrate leaching losses and N₂O emissions in this region.