Long-term Effects of Tillage and Corn Stalk Return on Soil Carbon Dynamics

Abstract

The ability to increase pools of soil organic C (SOC) in agricultural ecosystems is of interest both for sequestering atmospheric CO 2 , and for restoring organic matter pools important to soil health. It has been well established that tillage and harvest management regimes can influence SOC in cropland, but long-term, continuous experiments are rare. We investigated the dynamics of relic and new SOC pools using δ 13 C analysis in cornfields (Zea mays L.) established in 1972 at the University of Connecticut Research Farm. The plots have been under no-till (NT) or conventional till (CT) management, with residues returned (+) or residues removed (-) within each tillage treatment. After 28 yr of continuous management, NT increased SOC significantly by 48.3 ± 9.9 g C m -2 yr -1 over CT in treatments with residue returned (i.e., NT+ compared with CT+), and by 60.1 ± 13.8 g C m -2 yr -1 over CT in treatments with residue removed (i.e., NT- compared with CT-). Residue return in NT+ plots did not increase SOC relative to NT- plots (23.0 ± 12.7 g C m -2 yr -1 , N.S.), but residue return to the CT+ plots resulted in a significant increase in SOC of 34.8 ± 11.1 g C m -2 yr -1 over SOC content in CT- plots. The greatest difference in SOC content was found between the CT-and NT+ treatments (83.1 ± 10.7 g C m -2 yr -1 ). Our results indicate that there may be a rapid cycling of the aboveground C4-C back to the atmosphere as CO 2 or lost as dissolved organic C from the soil profile. Such a rapid cycling of returned C4-C suggests that the annual return of aboveground biomass may not increase soil C storage over the long term once soils have reached a steady-state SOC level.