INFLUENCES OF MULCH RATE AND SLOPE STEEPNESS ON INTERRILL EROSION.

Soil and water losses from plots representing field areas between rills were studied for four rates of straw mulch at four slope steepnesses. Three simulated rainstorms totaling 2 hours at 6. 4 cm/hour were applied to a 61- by 61-cm test area of Russell silt loam soil. Interrill erosion was reduced about 40% by mulch applied at a rate of only 0. 5 metric tons/ha and about 80% by 2 tons/ha, as compared with no mulch. Erosion was negligible at the 8 tons/ha rate. Soil losses from the interrill areas at 20% slope were only about double those measured at 2% slope, whereas widely used erosion equations show that total field erosion would increase about 20-fold over this range of steepnesses.