NITRATE NITROGEN CONCENTRATIONS IN PERCOLATE FROM LYSIMETERS PLANTED TO A LEGUME-GRASS MIXTURE

Growing concern that N from agricultural sources is a major pollutant of groundwater has stimulated research on NO3-N concentrations in groundwater under crops receiving N fertilizer. Knowledge of the effects of legumes on groundwater quality and their potential for reducing NO3-N concentrations is limited. Three Coshocton monolith lysimeters (Y-102A, B, and C) containing a well-drained silt loam soil on a 13% slope, and four lysimeters (Y103A, B, C, and D) containing a moderately well-drained silt loam soil on a 6% slope were used to study the effects of a legume-grass mixture on groundwater quality. Between experiments with corn (Zea mays L.), an alfalfa-orchard grass mix (70% Medicago sativa L. + 30% Dactylis glomerata L.), was grown for 2 yr and 3 yr on the Y102 and Y103 lysimeters respectively. The corn, some of which received high rates of N fertilizer, produced NO3-N concentrations in percolate ranging from 15 to 40 mg/L. Under alfalfa, NO3-N concentrations in leachate often were less than 5 mg/L, especially on the moderately well-drained lysimeters. The highest NO3-N percolate concentrations under all treatments occurred during the winter/early spring months.