Plant Nutrient Concentrations in Runoff from Fertilized Cultivated Erosion Plots and Prairie in Eastern South Dakota

Runoff waters from fertilized erosion plots and from native prairie in South Dakota were compared to determine the effect agriculture has had on water quality. Calcium, Mg, K, Na, total P, PO4‐P, NO3‐N , and NH4‐N contents were found to be similar in runoff from the erosion plots and from the prairie. The elemental contents in runoff from erosion plots planted to oats (Avena sativa L.), corn (Zea mays L.), and alfalfa (Medicago sativa L.) or fallowed were not distinctly different and varied from year to year. Variations in the ions in water collected from different basins in the prairie may be caused by differences (i) in the prairie vegetation and mulch in the drainage basins, (ii) in the time the runoff has to dissolve ions because of different overland flow distances, and (iii) in the dilution of the runoff by precipitation that falls directly into the basin. Losses of plant nutrients in soil eroded from cultivated land may be similar to average losses that would occur naturally if the area were in pristine prairie that was periodically subjected to fire.