Tillage effects on soil organic carbon storage and dynamics in Corn Belt of Ohio USA

No-till (NT) agriculture reduces soil disturbance, conserves soil and water, and lowers the cost of agricultural production. However, its role in soil organic carbon (SOC) sequestration can be soil and site specific. The applicability of the results from long-term tillage experiments (LTTEs) showing positive rate of carbon (C) sequestration is being questioned under large scale farmers' field conditions. Therefore, this study assessed the soil C dynamics under conventional till (CT) and NT practices using three LTTEs and three farmer's field sites in Ohio, USA with diverse soil types, and environmental and management conditions. The hypothesis tested was that reduced soil disturbance in NT management system enhances soil C sequestration in comparison to CT management. Soils were sampled (0-40cm) from adjacent CT, NT and woodlot (WL) plots at each site. Total C and nitrogen (N) pools were calculated based on equivalent soil mass basis. The SOC was fractioned into old C and new (corn C) using δ ¹³C natural abundance. The CT soils had 26-55% lower SOC and 7-34% lower N pool compared to forest soils. Most of the historic SOC and N losses in cultivated soils occurred within the plow (0-25cm) layer. The SOC pool in the top 40cm was significantly greater under NT than CT at LTTEs and Coshocton farm. There were no significant differences in SOC pool of the top 40cm among CT and NT at Delaware and Hoytville farms. Old C accounted for 69% and 66% of SOC under CT and NT, respectively at Northwestern Agricultural Research Station. However, at Western Agricultural Research Station, corn-derived C dominated CT and NT soils, accounting for 55% and 66% of SOC in the top 40cm, respectively. At North Appalachian Experimental watersheds, corn-derived C dominated NT soils (64%), while old C dominated CT soils (64%). Result of this study indicated that a decrease in SOC and N pools occurs when forest soil is cultivated. Conversion of CT to NT restores some of the depleted SOC and N pools. This supports our hypothesis that the reduced soil disturbance in NT system slows the decomposition of SOC which increases soil C sequestration. The quantity and rate of loss or sequestration depends on several factors including soil type, texture and drainage, tillage intensity, and duration of NT practice.