SOIL NITRATE PROFILES UNDER IRRIGATION ON COASTAL-PLAIN SOILS

Soil samples were taken from the surface to a depth of 152 cm on 16 irrigated sites and one forested site in the fall of 1983. All but one of the irrigation sites had corn grown on it in four out of the previous five years. Soil types of the irrigated sites were Matapeake silt loam, Sassafras sandy loam, Woodstown sandy loam, Rumford loamy sand, and Evesboro loamy sand. Soil samples were also taken in the fall of 1983 and spring of 1984 from irrigated corn plots where poultry manure and ammonium nitrate fertilizer were applied at a rate of 202 kg/ha of available nitrogen. Nitrate concentrations were lower on the forested site than any of the cropland sites. Nitrate leaching was occurring to some extent on all of the irrigated corn sites. The greatest nitrate concentrations in the soil profile occurred where excessive nitrogen was applied using manure in addition to commercial fertilizer. The site where soybeans had been grown in the previous four growing seasons had lower nitrate concentrations than any of the cropland sites. Nitrate concentrations were lower at greater depths on the com plots in the spring of 1984 than in the fall of 1983. The most dominant factor affecting fall nitrate profile levels is the total amount of nitrogen applied. © ASCE.