Managing ground water contamination from agricultural nitrates

Ground water contamination from agricultural nitrates poses potential adverse health effects to a large segment of the rural population of the United States. Contamination is especially prevalent in livestock intensive areas, which produce large quantities of animal waste with substantial nitrogen content.

In this study, potential management strategies for reducing nitrate contamination of ground water from agricultural sources were examined using an economic-physical model of a representative dairy farm in Rockingham County, Virginia. A mixed integer programming model with stochastic constraints on nitrate loading to ground water and silage production was used to simulate the impacts of various nitrate loading reduction strategies on estimated farm level net returns over variable costs. A survey of all dairy operations in the county was conducted to assist in specifying the mathematical programming model, identify current nutrient management and quality issues, and gauge farmers’ attitudes toward ground water quality and agricultural chemical use.

Results of the model indicate that substantial reductions in current nitrate loadings are possible with relatively minor impacts on farmers’ net returns through the use of currently practiced approaches of cost sharing for manure storage facility construction and nutrient management planning. Greater loading reductions are achievable through presently untried policies of land use restrictions, bans on purchase of commercial fertilizer, and imposition of standards on loadings to ground water. These reductions are achieved, however, at higher costs in terms of reduced net returns.

Study results indicate that a wide range of policy options exist for reducing nitrate loading to ground water; these reductions, while varying in cost, do not appear to come at the expense of eliminating the economic viability of the county dairy sector. Model results indicate that reductions in nitrate loading of 40 to 70 percent (on average) could be achieved with reductions in farmers’ net returns of one to 19 percent, respectively, when cost sharing for manure storage construction was provided. Explicit consideration was given to the annual variability in nitrate loading due to weather and other factors. The result was higher policy costs than when average loadings alone were considered.