Soil organic carbon sequestration rates in two long-term no-till experiments in Ohio

The effectiveness of no-till (NT) farming in reducing loss of soil organic matter (SOM) depends on climate and soil properties. Soil samples were obtained from two long-term experiments that were designed to study the impact of tillage systems on crop yields. However, the objectives of this experiment were to assess the impact of NT on soil organic carbon (SOC) sequestration rate and other soil properties and to estimate historic depletion of SOC under different soil management practices with reference to the undisturbed wooded control. The two long-term experiments in Ohio studied were those sited at South Charleston and Hoytville. The South Charleston, (83 degrees 30' W and 39 degrees 48' N) experiment was established in 1962 on Crosby silt loam (fine mixed, mesic Aeric Ochraqualf). The site has long-term annual temperature and precipitation of 10.8 degrees C and 1043 mm, respectively. Tillage treatments for continuous corn (Zea mays) were NT, chisel plow (CP), and moldboard plow (MP). The Hoytville (84 degrees 04' W and 41 degrees 03' N) experiment was established in 1987 on Hoytville clay loam (fine, illitic mesic Mollic Epiaqualfs) soil. The site has long-term annual temperature and precipitation of 9.9 degrees C and 845 rum, respectively. There were two crop rotations: (i) 2-year corn-soybean (Glycine max) rotation with NT and subsoiling and (ii) 3-year com-soybean-oat (Avena sativa) rotation with NT, CP, and rotational tillage soil management. The Hoytville clay site is poorly drained, has higher clay content, and higher and more even by distributed antecedent level of SOC in the soil profile than does the South Charleston silt loam soil. No-till increased SOC and N pools in the 0 to 5-cm layer in silt loam soil but had no effect in clay soil. The rate of SOC sequestration in the silt-loam soil under NT was 175 kg C ha(-1) y(-1). The silt loam soil had higher SOC and N stratification ratios in NT than in MP and CP treatments, whereas the stratification ratios were low and similar in all treatments in the clayey soil. For both soils, there were no differences between tillage treatments in several soil properties including texture, available water capacity, hydraulic conductivity (K), and cation exchange capacity. The NT decreased soil bulk density and pH in the 0 to 15-cm layer in the silt loam soil. The plow till treatments had a small impact on soil aggregation in clayey soil. The decline in water-stable aggregates with reference to NT was no more than one sixth. In the silt loam soil, however, the water-stable aggregates in plow till treatments were merely one third of that in the NT treatment. The historic loss of the SOC pool for 0 to 30-cm depth under agricultural land use was 25 to 35% in silt loam and 19 to 25% in the clayey soil.