Runoff losses of Nutrients and soil from ground fall-fertilized after soybean harvest

ABSTRACT PLOT measurements of soil and nutrient runoff concentrations and losses were made for two simulated rains in the fall after soybean harvest and fertilization (N, P, and K at 31, 35, and 80 kg/ha, respectively). The five treatments were: fertilizer surface-applied, no incorporation; fertilizer point-injected into the soil; fertilizer incorporated by chisel plowing; fertilizer incorporated by disking; and no fertilizer applied, no tillage. Chisel plowing reduced surface residue coverage from 82% (before tillage and the first rain) to 48%; disking reduced coverage to 31%. About half the residue buried by tillage was uncovered by the first rain. Sediment concentrations in runoff from the tillage plots were about three times higher than from the no-tillage plots. For rain 1(111 mm), loosening the soil by tillage reduced runoff amounts, particularly from the chisel-plow treatment; for rain 2 (72 mm), runoff from the disked treatment was about three times that from the other treatments. Total soil loss from the disk treatments was 2.3 T/ha, which was at least three times higher than any other treatment. Concentrations of NH4-N, P04-P, and K in runoff water and on sediment from treatments where fertilizer was incorporated by either point-injection or tillage were at the same levels as from the unfertilized treatment. Chemical concentrations from the surface-application-without-incorporation treatment were significantly higher than from all other treatments, particularly for the first rain (e.g., NH4-N > 3 mg/L, P04-P > 0.9 mg/L, and K > 18 mg/L). Total NH4—N, P04—P, and K losses were also the greatest for the surface-application-without-incorporation treatment, but were only 0.8, 0.4, and 5.9 kg/ha, respectively. On the basis of these results, fall fertilization would not be recommended because of water quality concerns. If fertilizer is applied, no tillage should be performed because of the potential for increased soil losses; but if tillage is performed, chisel plowing would be preferred to disking. When point-injection of liquid fertilizers becomes feasible on a large scale, its advantage of nutrient incorporation without residue incorporation will warrant its recommendation.
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