No-Till Corn after Bromegrass: Effect on Soil Carbon and Soil Aggregates

Authors

Ronald F. Follett, Colorado State University - Fort CollinsFollow
Gary E. Varvel, University of Nebraska-LincolnFollow
John M. Kimble
Kenneth P. Vogel, University of Nebraska-LincolnFollow

Document Type

Article

Date of this Version

4-4-2008

Comments

Published in Agron. J. 101:261–268 (2009). Copyright © 2009 by the American Society of Agronomy.

Abstract

Grasslands in the Conservation Reserve Program (CRP) in the USA may be converted to grain crops for bioenergy. The effect of no-till conversion of a smooth bromegrass (Bromus inermis Leyss) grassland to no-till corn (Zea mays L.) production on soil organic carbon (SOC) in the western Corn Belt was monitored for over 6 yr. A different ¹³C/¹²C isotope signature is imparted to SOC by C4 plants including corn versus C3 plants such as bromegrass. Changes in C isotope ratios in SOC in three soil depths (0- to 5-, 5–10, and 10–30 cm) by particle size was also monitored during ~6.5 yr of no-till corn production at two different N levels (60 and 120 kg ha^–1). Soil was collected eight times during the study from the 0- to 5- and 5- to 10-cm depths, and at four of these times from the 10- to 30-cm depth from each of the N rate replicates. Because fertilizer N had no significant effect over years on any of the above-ground biomass production variables, the data from both N treatments was combined for regression analysis to determine the effects of years of no-till corn production on SOC variables. Total SOC did not change significantly at any depth during the study, but there was a significant change in the source of the SOC. Total C4-C increased over this time, while C3-C decreased in the 0- to 5- and 5- to 10-cm depth, while neither changed in the 10- to 30-cm depth. In the 0- to 5- and 5- to 10-cm depths, largest loss of C3-C was from 2-mm aggregates, while largest increases in C4-C were in the 1-, 0.5-, 0.25-, and 0.125-mm aggregates. If CRP grasslands are converted to grain crop production, the data from this study strongly support the use of no-till farming practices as a method of conserving the SOC that was sequestered during the time period that the land was in the CRP.