NITROGEN AND PHOSPHORUS IN ERODED SEDIMENT FROM CORN AND SOYBEAN TILLAGE SYSTEMS

Runoff, soil loss and sediment bound total Kjeldahl nitrogen (TKN) and Bray P-1 phosphorus (P) losses were measured from corn (Zea mays L.) and soybean [Glycine max (L.)] tillage systems subjected to simulated rainfall. Runoff and soil loss were influenced by contouring and tillage treatment. After 60 min of simulated rainfall, there was little or no runoff or soil erosion from plots which had recently been ridge cultivated along the contour. Soil and nutrient losses from up-and-down slope ridge-till plots were never significantly different than from the conventional tillage treatment. Bray P-1 P concentration in the top 5 cm of soil and eroded sediment was significantly reduced by moldboard plowing. Concentrations of Bray P-1 in the eroded sediment tended to decrease as soil loss increased. Bray P-1 enrichment ratios ranged from 1.69 to 4.5, and were correlated to a greater extent with sediment concentration than with soil loss. The TKN losses were linearly related with soil loss and the average TKN enrichment ration ranged from 1.02 to 1.28. The TKN enrichment ratio was not significantly correlated with Bray P-1 enrichment ratio.