Spatial Patterns of Water and Nitrogen Response Within Corn Production Fields

Abstract

Agricultures role on environmental quality has been debated for many decades and although there has been advances in our understanding of the linkage between agricultural management and environmental quality, there is still much we don’t understand about the combination of field-scale and watershed scale management changes (Hatfield et al., 2009). There is increasing interest in developing solutions to environmental quality problems originating from agricultural management; however, the challenge remains on how we integrate the pieces of a very complex puzzle together to achieve solutions which transcend space and time scale. Within the Midwestern United States, the reoccurrence of the hypoxic zone within the Gulf of Mexico and the large increase in the size of the hypoxic zone after the 1993 floods in the Midwest focused attention on the role of agriculture in nonpoint source pollution. Burkart and James (1999) evaluated the nitrogen (N) balance for the Mississippi River Basin and concluded that mineralization of soil organic matter and application of commercial fertilizer was two primary contributors to N load. Jaynes et al. (1999) after examination of a small watershed (5400 ha) in central Iowa found that nitrate-N losses averaged 20 kg ha-1 for this watershed and reached a level in excess of 40 kg ha-1 during 1993. Hatfield et al. (1998) found that drainage from Walnut Creek was the primary transport pathway for nitrate and the annual loads were related to precipitation differences among years. Hatfield et al. (1999) found that for Walnut Creek watershed that drainage through the subsurface drain lines accounted for approximately half of the annual precipitation with evapotranspiration accounting for the other half. This movement of water through the soil profile and the solubility of nitrate in water produce large amounts of nitrate-N loss (Jaynes et al, 1999). These results suggested a strong link between precipitation, crop water use patterns, and nitrate losses. Occurrence of the hypoxic zone has prompted an increased level of debate about the need to reduce N inputs into agricultural systems. Opponents of this conclusion argue that over the past 20 years the input of N fertilizer has not increased, soil organic matter levels haven’t changed, and crop production levels have increased suggesting that the efficiency of the agronomic production system has increased and any change in nitrate loss would be difficult to achieve. Hatfield et al. (2009) performed an analysis of the temporal changes in the nitrate-N concentrations in the Raccoon River watershed in central Iowa and observed the changes in nitrate-N concentrations since the 1970’s were dominated more by changes in land use practices