Tillage effects on soil organic carbon distribution and storage in a silt loam soil in Illinois

Interest in tillage impacts on sequestration of soil organic carbon (SOC) has increased greatly during recent years. The use of reduced and no-tillage (NT) practices generally increases the SOC concentration in surface few centimeters when compared to conventionally tilled soils. However, use of conservation tillage does not always result in increased SOC storage overall. The effects of sample handling and data expressions on the assessment of tillage-induced SOC sequestration were investigated using data collected from a tillage trial on a Thorp silt loam (US Taxonomy: fine-silty, mixed, mesic Argiaquic Argialboll; FAO: Orthic Greyzems). The tillage experiment was established in 1986 in Illinois, USA. The NT treatment used no soil disturbance except for planting. The disk tillage treatment included fall disking (7.5-10 cm deep) after corn (Zea mays L.) and spring field cultivation after soybean (Glycine max L.) production. The moldboard plowing treatment included fall moldboard plowing (20-25 cm deep) after corn, followed by spring disking (7.5-10 cm deep) and field cultivating; fall chisel plowing (30-35 cm) was done after soybean, followed by spring disking and field cultivation. Estimates of tillage impacts on SOC sequestration varied with the soil depth considered, time of sampling, and sample handling technique. Results indicated that tillage-induced changes in SOC occurred in the surface 30 cm. NT soil had greater C contents in the upper 30 cm when assessed on a concentration and volumetric basis. Although the use of NT practices did increase C content stored as surface residues and SOC concentrations in the top few cm of the soil, it did not increase SOC storage overall.