Potential Purification of High Nitrate Groundwater Through Irrigation Management

ABSTRACT Afield-calibrated computer model was used to evaluate the effect of irrigation and nitrogen (N) management upon corn production and the potential for decreasing the nitrate concentration of the groundwater (purification). The study site is representative of a large portion of the Central Platte Valley of Nebraska where sandy soils, 10 to 40 ppm of nitrate-nitrogen (NO3-N) in the groundwater, and a shallow water table are common. Pumped groundwater is the primary source for irrigation in the valley. Simulation results for this area indicate that irrigation and N management strongly influence corn production and the increase or decrease of groundwater nitrate. For locations with concentrations less than 20 ppm N03-N in the groundwater, more N percolates from the crop root zone than is pumped in the irrigation water. This pollu-tion is minimized when water and N are carefully man-aged to meet crop requirements. When concentrations exceed 20 ppm the crop can, under certain conditions, extract more nitrate from the pumped irrigation water than is returned to the groundwater through leaching. Excessive irrigation amplifies the nitrate purification potential over a wide range of water application amounts as long as fertilizer rates are low and the nitrate concen-tration of the irrigation water is high. If excessive fertili-zer is applied, the opportunity for purification is lost.