Nitrogen losses from Midwestern watersheds : implications for nitrogen management policies
Nitrogen is an essential element in our natural environment, and especially critical for crop production to maintain economic yield from crop production. Nitrogen is considered a major contributor for the Northern Gulf of Mexico hypoxic zone. Nitrogen losses from agriculture are the cause for concern because of the increasing scientific data suggesting N is the leading cause of the hypoxic zone. This interpretation leads the public to believe that agricultural N needs to be regulated. Past research suggests that nitrate concentrations in the Upper Midwest streams and rivers have high nitrate levels due to fertilizers. These studies have been done on large-scale watersheds, which implicates that smaller tributaries are responsible for the increasing amount of N concentrations in the Mississippi River Basin. This study evaluates the N loss from selected smaller tributaries of the Upper Midwest, their N concentrations, and the amount of fertilizer applied in five Midwestern states; Illinois, Iowa, Minnesota, Missouri, and Wisconsin. A loss of N was found from every state but a large variation exists within and among states. Higher application rates of N in Iowa and Illinois create greater N loadings in these watersheds. A consistent trend in the amount of N lost vs. applied was not found in the watersheds evaluated. This study illustrates the amount of N does need to be reduced, but it shows no significant relationship from the amount applied to the amount lost. Therefore, nutrient management should be based on the practices for managing N application and N loss.