Surface residue effects on soil erosion from ridges of different soils and formation

The effect of crop residue on soil erosion by water was studied on three soils using well-defined, ridge-furrow configurations to simulate ridge-tillage conditions. Interrill and rill erosion was studied using rainfall simulation on freshly formed (FF) and consolidated (CON) ridges on somewhat poorly drained Rossmoyne silt loam in Ohio, and on freshly formed ridges on well-drained Chelseafine sand and Miami silt loam in Indiana. Corn stalk and leaf residue were hand-applied only to rill erosion plots. Average percent cover for five residue levels was 0, 4.7, 10.0, 20.0, and 45.0%. Average interrill detachment rate on consolidated Rossmoyne ridges was significantly smaller than that from Miami and Rossmoyne freshly formed ridges. Average runoff rate for consolidated Rossrnoyne ridges was significantly greater than that on freshly formed ridges. Average rill detachment rate decreased in the order of Chelsea FF > Rossmoyne FF > Miami FF > Rossmoyne CON. Within each inflow level for Chelsea freshly formed and Rossmoyne consolidated ridges, average detachment rate decreased significantly; 51 to 83% and 88 to 92% reductions, respectively, as cover increased from 0 to about 45%. Within each inflow level for Chelsea freshly formed ridges, detachment rate decreased significantly by 40 to 72% as cover increased from 0 to about 20%. Cover levels of 20 and 45% bracket a compliance level of 30%. On Miami soil, as cover increased from 0 to about 45%, detachment decreased by 65 to 82%. For Detachment = a exp (b X % residue cover), average coefficient b values were Chelsea freshly formed ridges, b = -0.032; Miami freshly formed ridges, b = -0.030; Rossmoynefreshlyformed ridges, b = -0.006; and Rossmoyne consolidated ridges, b = -0.061. As residue increased from 0 to approximately 45%, average flow velocity decreased significantly by 55 to 71%. Addition of 40% residue cover decreased velocity of flow across all flow levels and soils by more than 50%. Reduction was greater for consolidated Rossmoyne ridges compared to freshly formed ridge conditions. Addition of residue at approximately 45% increased the Darcy-Weisbach friction factor by 9 to 29 times that of bare soil. Effect was greatest for noncohesive Chelsea sand. For freshly formed ridge conditions, a linear relationship was found for detachment rate versus hydraulic shear on all soils with no residue cover. As residue cover increased, correlation between detachment rate and hydraulic shear exhibited much variability. The model fit the data reasonably well (r2 values of 0.6 to 0.9) for cases where there was no, or relatively small amounts, of residue on freshly formed ridges. For Rossrnoyne consolidated ridges, correlation between detachment and hydraulic shear for all residue levels was very low. For freshly formed ridge conditions, the interrill contribution was a smaller portion of total detachment. On consolidated Rossmoyne ridges, the interrill contribution was a major portion of total detachment all along entire range of hydraulic shear values evaluated in this study. Further research is needed to quantify surface residue-soil disturbance interactions for ridge-tillaged especially for conditions following planting, cultivation, and harvest.