HISTORIC ASSESSMENT OF AGRICULTURAL IMPACTS ON SOIL AND SOIL ORGANIC CARBON EROSION IN AN OHIO WATERSHED

Agricultural management affects soil and soil organic carbon (SOC) erosion. The effect was assessed for a watershed (0.79 ha, 10% slope steepness, 132 m slope length) at the North Appalachian Experimental Watershed research station near Coshocton, Ohio, from 1951 to 1998. The agricultural management included: (i) plow-till corn (Zea mays L.)-wheat (Triticum aestivum L.)-meadow-meadow rotation (CWMM) from 1951 to 1970, (ii) plow-till continuous corn (CC) from 1971 to 1975, (iii) meadow (M) from 1976 to 1983, and (iv) no till corn-soybean (Glycine max (L.) Merr) rotation (CS) from 1984 to 1998. Soil erosion was assessed by sediment collection, the Revised Universal Soil Loss Equation (RUSLE), and the 137Cesium (137Cs) method. The SOC erosion was computed as a product of the soil erosion multiplied by the SOC content of 1.51% in the surface soil and by the SOC enrichment ratio of 1.71 except for the proportional equation of the 137Cs method. Sediment collection measurements indicated that the annual soil and SOC erosion rates (Mg ha−1 yr−1) for the corn cycles were, respectively, 1.55 and 0.040 for CWMM, 5.88 and 0.15 for CC, 0.63 and 0.016 for CS, and 2.34 and 0.060 for the entire period. The rates were, respectively, 0.35 and 0.009 for wheat cycles, 0.63 and 0.016 for soybean cycles, and essentially zero for meadow. Furthermore, the rates for the crop rotation periods were, respectively, 0.50 and 0.013 for CWMM, 5.88 and 0.15 for CC, 0.63 and 0.016 for CS, and 1.02 and 0.026 for the entire study period. The estimates by the RUSLE and proportional equation were 3 to 14 and 10 to 55 times the sediment values, respectively. However, the estimates by the revised exponential equation were 1 to 3 times the sediment values.