Strength properties and organic carbon of soils in the North Appalachian region

Soil strength influenced by management and soil properties controls plant growth, root development, and soil-moisture relations. The impact of textural and structural parameters on soil strength is moderated by soil organic C (SOC) concentration. Therefore, the objectives of this study were to assess differences in soil strength and SOC concentration in watersheds under long-term (> 15 yr) management practices in the North Appalachian region on a predominantly Typic Hapludults on undulating slopes (> 6% slope). Seven watersheds without field replication under moldboard plow (MP), chisel plow, disk with beef cattle manure (DiskM), no-till with beef cattle manure (NTm), no-till with no beef cattle manure (NTnm), pasture, and forest were studied. Cone index (0), shear strength, bulk density (p(b)), volumetric moisture content (theta(v)), and SOC concentration were determined at the summit, backslope, and footslope landscape positions at the 0- to 10-, 10- to 20-, and 20- to 30-cm depths. The SOC concentration was slightly higher at the footslope than at the summit position in the cultivated watersheds. The P-b was lower at the footslope than at the summit in NTm (1.22 vs. 1.42 Mg m(-3)) and chisel (1.34 vs. 1.47 Mg m(-3)) treatments. Forest had the lowest CI (0.19 MPa), shear strength (6.11 kPa), and P-b (0.93 Mg m(-3)) and the highest SOC concentration (62.7 g kg(-1)), whereas NIP had the highest CI (0.67 MPa), shear strength (25.5 kPa), p(b) (1.44 Mg m(-3)), and the lowest SOC concentration (13.6 g kg(-1)) in the 0- to 10-cm depth (P < 0.01). The SOC concentration in NTm was 1.7 times higher than that in NTnm, and both no-till treatments had lower P-b (< 1.21 Mg m(-3)) than MP (1.44 Mg m(-3)) at 0- to 10-cm depth (P < 0.01). Manuring decreased both CI and shear strength, but increased SOC concentration. The p(b), theta(v), and SOC concentration were potential predictors of Cl; whereas p(b) and SOC concentration were of shear strength (r(2) > 0.42; P < 0.01). Results show that landscape positions had small effect, but management, particularly manuring, had large and significant effects on soil strength and SOC concentration.