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 thr ee soils using well-defined, ridge-furrow configurations to simulate r idge-tillage conditions. Interrill and rill erosion was studied using rainfall simulation on freshly formed (FF) and consolidated (CON) ridg es on somewhat poorly drained Rossmoyne silt loam in Ohio, and on fres hly formed ridges on well-drained Chelsea fine sand and Miami silt loa m in Indiana. Corn stalk and leaf residue were hand-applied only to ri ll 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 cons olidated Rossmoyne ridges was significantly smaller than that from Mia mi and Rossmoyne freshly formed ridges. Average runoff rate for consol idated Rossmoyne 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 inf low 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, detachmen t 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%, detachmen t 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; Rossmoyne freshly fo rmed ridges, b = 0.006; and Rossmoyne consolidated ridges, b = 0.061. As residue increased from 0 to approximately 45%, average flow velocit y decreased significantly by 55 to 71 %. Addition of 40% residue cover decreased velocity of flow across all flow levels and soils by more t han 50%. Reduction was greater for consolidated Rossmoyne ridges compa red to freshly formed ridge conditions. Addition of residue at approxi mately 45% increased the Darcy-Weisbach friction factor by 9 to 29 tim es 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 resid ue cover. As residue cover increased, correlation between detachment r ate and hydraulic shear exhibited much variability. The model fit the data reasonably well (r(2) values of 0.6 to 0.9) for cases where there was no, or relatively small amounts, of residue on freshly formed rid ges. For Rossmoyne 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 port ion of total detachment. On consolidated Rossmoyne ridges, the interri ll contribution was a major portion of total detachment all along enti re range of hydraulic shear values evaluated in this study. Further re search is needed to quantify surface residue-soil disturbance interact ions for ridge-tillage, especially for conditions following planting, cultivation, and harvest.