Effects of Increased Fertilizer Rates on Nitrogen Content of Runoff and Percolate From Monolith Lysimeters

Nitrogen (N) fertilizer was applied to meadow (Danthonia spicata L., Poa pratensis L., and Medicago sativa L. Dactylis glomerata L.)- and corn (Zea mays L.)-cropped lysimeters at rates up to 322 and 672 kg/ha per year, respectively, to determine the effects on chemical quality of surface and subsurface water. Runoff and percolate samples collected from May 1971 through April 1975 were analyzed for inorganic and total N content. Results were evaluated from crop and soil cover treatment differences and compared with data from a similar, earlier study on the same lysimeters in which very low rates of N fertilizer were used. Nitrogen losses in runoff were greatest in the summer when intense rainfall events occurred shortly after the date of fertilizer application. Quantities of N transported in surface water decreased as the amount of effective soil cover increased. The N losses ranged from < 1 kg/ha per year for meadow to 10 kg/ha per year for clean cultivated corn. Nitrogen loss by leaching was greatest during the winter when percolation rates increased because of low evapotranspirational demand. Differences observed among management practices were primarily a function of the levels of soluble N remaining in the soil at the end of the growing season. Nitrogen flux was < 10 kg/ha per year under meadow, with N concentrations in the percolate not exceeding the 10 ppm NO₃-N level recommended for potable water by the U. S. Public Health Service. More than 250 kg/ha per year of N loss was measured under corn, with N concentrations in percolating water attaining 70 ppm—far in excess of recommended levels. Results of this study demonstrated that improved fertilizer management, involving application rates in balance with crop nutrient requirements, soil incorporation of fertilizer materials, and adequate soil cover, will minimize runoff and leaching losses which reduce fertilizer efficiency and adversely affect water quality.