Date of this Version
Balancing the amount of N needed for optimum plant growth while minimizing the NO3 that is transported to ground and surface waters remains a major challenge for everyone attempting to understand and improve agricultural nutrient use efficiency. Our objectives for this review are to examine how changes in agricultural management practices during the past century have affected N in Midwestern soils and to identify the types of research and management practices needed to reduce the potential for nonpoint NO3 leakage into water resources. Inherent soil characteristics and management practices contributing to nonpoint NO3 loss from Midwestern soils, the impact of NO3 loading on surface water quality, improved N management strategies, and research needs are discussed. Artificial drainage systems can have a significant impact on water quality because they behave like shallow, direct conduits to surface waters. Nonpoint loss of NO3 from fields to water resources, however, is not caused by any single factor. Rather, it is caused by a combination of factors including tillage, drainage, it is caused by a combination of factors, including tillage, drainage, crop selection, soil organic matter levels, hydrology, and temperature and precipitation patterns. Strategies for reducing NO3 loss through drainage include improved timing of N application at appropriate rates, using soil tests and plant monitoring, diversifying crop rotations, using cover crops, reducing tillage, optimizing N application techniques, and using nitrification inhibitors. Nitrates can also be removed from water by establishing wetlands or biofilters. Research that is focused on understanding methods to minimize NO3 contamination of water resources should also be used to educate the public about the complexity of the problem and the need for multiple management strategies to solve the problem across agricultural landscapes.