The Effect of Crop Residues on Soil and Water Losses from Corn and Winter Wheat

Soil and water losses from plots planted to a corn, winter wheat, and lespedeza rotation were measured for 14 years. The plots, located on Grantsburg silt loam were 70 feet long and on slopes of 5% and 9%. During the period 1939–46, crop residues were removed or grazed from the plots. From 1947 through 1953, crop residues were returned to the plots. The average annual precipitation was 3 inches greater during the 1947–53 period than in the 1939–46 period. The maximum rainfall intensity (15-minute period) for the storms producing over 80% of the total soil loss was highly significantly greater during the 1947–53 period, when crop residues were returned, than in the 1939–46 period, when crop residues were removed. Comparable individual storms that produced over 80% of the total soil loss were analyzed for each of the two periods. Soil loss “per inch of rain” from corn plots was over three times greater when residues were removed than when they were returned on both the 5% and 9% slopes. Soil loss “per inch of rain” from winter wheat plots on the 5% slope was 3.9 times greater, and on the 9% slope 2.4 times greater when the residues were removed than when they were returned. During the 1947–53 period, soil losses from winter wheat plots were more than 2 times greater from 9% slopes and over 3 times greater from 5% slopes than from similar plots planted to corn. Crop residues on the surface reduced soil losses but did not materially change the amount of runoff from soils having a very slowly permeable subsoil. Data from individual storms producing over 80% of the total soil loss from winter wheat plots for the 1939–53 period were analyzed by the multiple regression method. The partial regression coefficient was determined between soil loss per inch of precipitation and rainfall intensity in inches per hour for the most intense 15-minute period. Keeping the variables of antecedent rainfall and total precipitation constant, the analysis indicated significant differences (1) between the rate of soil loss on 9% slopes where residues were returned as compared to where they were removed, and (2) between the rate of soil loss on 5% slopes as compared to 9% slopes where all residues were removed.