Environmental Effects of a Medium-Fertility 12-Month Pasture Program: II. Nitrogen
1982
Owens, L. B. | van Keuren, R. W. | Edwards, W. M.
Four small, medium fertility (56 kg/ha per year N) watersheds were used in a rotational summer-grazing and winter-feeding program to determine its effects on N levels in water. During a 5-year study on sloping uplands in Ohio, the concentrations of NO₃-N and NH₄-N were determined in precipitation, surface runoff, subsurface flow, and sediment. Although the NO₃-N concentration was generally higher in the surface runoff from the summer-grazing/winter-feeding area than from the summer-grazing-only areas, it usually resulted in no significant impairment of water quality, except on a few occasions when the NO₃-N concentration exceeded 10 mg/liter. The N transported in the subsurface flow from the summer-grazing only areas was approximately equal to that transported from the winter-feeding area and to the amount of N received in the precipitation. Both surface runoff transport and sediment transport of N were much greater in the winter-feeding area than in the summer-grazing-only areas because these latter areas yielded very little surface runoff and only a trace of soil loss. Reduction of vegetative cover and increased soil disturbance on the winter-feeding area resulted in increased surface runoff and soil erosion and thus more N was transported. Surface and subsurface losses of N from the winter-feeding area were nearly equal. A large percentage of N was transported by the large storms, which represented a small percentage of the total number of storms.
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