CARBON AND NITROGEN STORAGE ARE GREATER UNDER BIENNIAL TILLAGE IN A MINNESOTA CORN-SOYBEAN ROTATION

Authors: Venterea, Rodney - Rod; Baker, John; Dolan, Michael; Spokas, Kurt

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/2006
Publication Date: 8/22/2006
Citation: Venterea, R.T., Baker, J.M., Dolan, M.S., Spokas, K.A. 2006. Carbon and nitrogen storage are greater under biennial tillage in a Minnesota corn-soybean rotation. Soil Science Society of America Journal. 70:1752-1762.

Interpretive Summary: There is increasing attention being paid to the role of agriculture in generating greenhouse gases that may affect global climate. The objective of this study was to examine how different plowing practices, applied over a 15-year period, affected the release of carbon dioxide (CO2) to the atmosphere, and the accumulation of carbon stored in the soil profile in corn/soybean rotations in Minnesota. The three tillage treatments were designed to represent a gradual gradient in intensity. The treatments ranged from the most physically disruptive conventional tillage (CT) employing moldboard plowing and disk ripping in alternate years, to an intermediate conservation tillage (CsT) employing disk ripping and no tillage in alternate years, to the least intensive no till (NT). Following the initial decade of treatments, only the intermediate treatment (CsT) accumulated carbon over the entire soil profile to a depth of 60 cm. The rate of accumulation under CsT was high compared to other studies. Over the last 5 years, neither of the reduced tillage treatments showed gains in carbon over the entire sampled depth. During a drier than normal growing season (2003), soil CO2 emissions and soil water content under CsT and NT tended to be higher than CT. In contrast, during a normally wet year (2004), no differences in CO2 emissions were detected. These findings have important implications for scientists and policy-makers involved in the development of strategies for minimizing the contribution of agriculture to atmospheric CO2 levels. In particular, the results demonstrating that a tillage practice of intermediate intensity was able to accumulate considerable soil carbon compared to both more intensive and less intensive tillage, should be considered in the development of such strategies for the upper midwest U.S.

Technical Abstract: Few studies have examined the impacts of rotational tillage regimes on soil carbon (C) and nitrogen (N). We measured the C and N content of soils managed under corn (Zea mays L.)-soybean (Glycine max L.) rotation following 10 and 15 years of treatments. A "conventional" tillage (CT) regime employing moldboard and chisel plowing in alternate years was compared with both continuous no-till (NT) and biennial tillage (BT) which employed chisel plowing prior to soybean only. While masses of C and N in the upper 0.3 m under both BT and NT were higher than CT, only the BT treatment differed from CT when the entire sampled depth (0.6 m) was considered. Decreased C inputs, as indicated by reduced grain yields, may have limited C storage in the NT system. Thus, while more C was apparently retained under NT per unit of C input, some tillage appears necessary in this climate and cropping system to maximize C storage. Soil carbon dioxide (CO2) fluxes under NT were greater than CT during a drier than normal year, suggesting that C storage may also be partly constrained under NT due to wetter conditions that promote increased soil respiration. Increased temperature sensitivity of soil respiration with increasing soil moisture was also observed. These findings indicate that long-term biennial chisel plowing for corn-soybean in the upper mid-west U.S. can enhance C storage, reduce tillage-related fuel costs, and maintain yields compared with more intensive annual tillage.