Effects of corn residue and fertilizer management on soluble nutrient runoff losses.

ABSTRACT SIMULATED rainfall was used to determine the ef-fects of fertilizer rate and placement, and corn residue amount on the soil surface, on soluble nutrient runoff losses from a fallow soil. Four levels of residue (0, 375, 750, and 1500 kg/ha), two levels of fertilization (none versus 77, 66, and 27 kg/ha of NH4-N, NO3-N, and PO4-P, respectively), and two methods of fertilizer place-ment were evaluated. On plots with no residue, the chemicals were either surface-applied or point-injected to a depth of 5 cm; on plots with residue, chemicals were surface-applied either above or below the residue. Bromide, at the rate of 151 kg/ha, also was applied to the fertilized plots. Residue on the unfertilized plots increased nutrient concentrations in runoff little, if at all. Surface fertiliza-tion significantly increased nutrient concentrations in runoff, particularly for the ions interacting with soil (NH4 and POJ). Placement with respect to corn residue did not significantly affect concentrations in runoff. In-jected fertilizer did not increase concentrations in runoff relative to concentrations for unfertilized plots. Concen-trations of nonadsorbed NO3 and Br~ ions in runoff from plots receiving chemical application were closely cor-related. Increases in losses of NO3-N and Br over unfer-tilized plots were less than 1 percent of that applied. In-creases in NH4-N and PO4-P losses from fertilization were as high as 5 and 3 percent of that applied, respec-tively.