Interrill Erosion as an Index of Mined Land Soil Erodibility

Abstract

ABSTRACT A rainfall simulation technique was used to evaluate the influence of slope steepness (3 and 9%), mulch rate (0, 1.12 and 2.24 t/ha), and antecedent soil moisture condition (dry and wet runs), on runoff, splash, soil loss in runoff and the primary particle composition of soil in splash and sediment from interrill areas on two mined land topsoils. Topsoils were obtained from stockpiles at North American Coal Corporation's Falkirk Mine near Underwood, ND, and Indian Head Mine near Zap, ND. Soil type and slope had no affect on interrill runoff while mulch rate of 2.24 t/ha reduced runoff by 30% during dry runs. Surface mulching was ineffective in reducing runoff during the wet runs. In terms of soil loss in runoff, the Falkirk topsoil was 28% more erodible than the Indian Head topsoil. Splash and soil loss rates increased with increased slope steepness. Mulch rates of 1.12 and 2.24 t/ha resulted in overall reductions in splash erosion of 56% and 73%, respectively, and reductions in soil loss in runoff of 42% and 64%, respectively, from the bare soil treatments. Splash erosion decresaed by 19% and soil loss in runoff increased by 28% during the wet runs when averaged for all other treatments. Soil in splash was enriched in sand while interrill sediment was enriched in clay and fine silt. The clay and fine silt enrichment of sediment was greater at 3% slope than 9% and also increased with the addition of surface mulch. Antecedent soil moisture condition did not influence the primary particle composition of soil in splash or interrill sediment. Interrill soil loss data were used to rank the erodibility of the topsoils according to slope and mulch rate variations through the development of an erodibility ratio index (ERI).