Soil-profile distribution of organic C and N at the end of 6 years of tillage and grazing management

Authors: Franzluebbers, Alan; STUEDEMANN, JOHN - Retired ARS Employee

Submitted to: European Journal of Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/21/2013
Publication Date: 10/1/2013
Publication URL: http://handle.nal.usda.gov/10113/57859
Citation: Franzluebbers, A.J., Stuedemann, J.A. 2013. Soil-profile distribution of organic C and N at the end of 6 years of tillage and grazing management. European Journal of Soil Science. 64:558-566.

Interpretive Summary: Soil organic carbon and total soil nitrogen are key determinants for evaluating the most beneficial agricultural management practices to address climate change, environmental quality, and soil productivity issues. A scientist at the Plant Science Research Unit in Raleigh, North Carolina teamed with a former scientist in USDA-Agricultural Research Service from Watkinsville, Georgia to evaluate the effects of tillage and cover crop management on carbon and nitrogen concentrations in the soil profile under long-term management. Soil organic carbon was affected by management only in the surface layer (0-8”), wherein soil under no tillage had greater content than under conventional, disk tillage. Preservation of carbon and nitrogen in the soil can help mitigate greenhouse gas emissions. In addition, conservation management of soil with no tillage and periodic utilization of cover crop forage for cattle grazing can be considered adaptation strategies to increase the resilience of agriculture in the southeastern USA to climate change. Findings from this study will be important for producers to understand the value of tillage management on soil carbon and nitrogen, as well as for conservation organizations and government agencies wanting to promote conservation practices to sequester carbon from the atmosphere and avoid transport of nitrogen from agricultural fields.

Technical Abstract: Stocks of soil organic carbon (SOC) and total soil nitrogen (TSN) are key determinants for evaluating agricultural management practices to address climate change, environmental quality, and soil productivity issues. We determined SOC, TSN, and particulate organic C and N depth distributions and cumulative stocks in response to 6 years of tillage (conventional and no tillage) and cover crop management (without and with cattle grazing) on an Acrisol in the southeastern USA. Total and particulate organic C concentrations were greater under no tillage than under conventional tillage at a depth of 0-20 cm only. No differences in concentrations at various depths to 150 cm or of cumulative stocks were observed in total and particulate organic C and N in response to cover crop management, suggesting that animal grazing had no negative effect on SOC and TSN. Compared with perennial grass as a control, stock of SOC was significantly reduced under cropping at a depth of 0-40 cm, was trending toward reduction at a depth of 0-90 cm, and was not different at a depth of 0-150 cm. Declining significance of management with depth indicated an important consideration in attempts to determine whole-profile response of SOC and TSN to management – rigorous sampling approaches are needed to overcome low concentrations and high variation with increasing soil depth. Results of this study clearly indicate (1) greater SOC and TSN concentrations can be expected in the surface layer under no tillage than under conventional tillage in Acrisols of the warm, moist climatic region of the southeastern USA and (2) compensation for stratified SOC and TSN with no tillage does not occur deeper in the soil profile, such that the same relative numeric difference that occurred at the surface remains unchanged with greater cumulative depth.