Rice (Oryza sativa L.) production systems have a greater global warming potential than upland crops because of methane (CH4) emissions resulting from anaerobic conditions of the flooded soils. Differences in cultural practices, cultivar choice, previous crop/crop rotation, and in particular soil texture may substantially influence CH4 emissions throughout the rice growing season. Despite being the leading rice-producing state in the United States, no research on CH4 emissions from clay soils has been conducted in Arkansas. The objective of this study was to characterize growing-season CH4 fluxes and emissions from direct-seeded, delayed-flood rice grown on a Sharkey clay soil (very-fine, smectitic, thermic Chromic Epiaquerts). Field research was conducted in 2012 evaluating bare soil (i.e., unvegetated) and non–N-fertilized and N-fertilized rice. Methane fluxes increased during vegetative growth in both vegetated treatments and reached significantly different maximum fluxes of 4.8 (N-fertilized) and 0.94 (non–N-fertilized) mg CH4-C m−2 h−1 following 50% heading. Fluxes then decreased over time in vegetated treatments and approached 0 mg CH4-C m−2 h−1 at flood release. Fluxes from the bare soil remained near 0 mg CH4-C m−2 h−1 for the entire growing season. Total season-long emissions were greater (P < 0.001) in the N-fertilized (35.6 kg CH4-C ha−1) compared with the non–N-fertilized (9.0 kg CH4-C ha−1) and bare soil (1.8 kg CH4-C ha−1) treatments, which did not differ with each other. Methane emissions from a clay soil in this study represented only 20% of the U.S. Environmental Protection Agency–reported emissions factor for rice grown in Arkansas. These results indicate that CH4 emissions from Arkansas rice produced on clay soils may be substantially overestimated, and additional data are needed to accurately evaluate the multitude of factors known to affect CH4 emissions.
1Department of Crop, Soil, and Environmental Sciences, University of Arkansas, Fayetteville, AR.
2Department of Plant, Soil, and Entomological Sciences, University of Idaho, Aberdeen Research and Extension Center, Aberdeen, ID.
3Agricultural Statistics Laboratory, University of Arkansas, Fayetteville, AR.
Address for correspondence: Dr. Kristofor R. Brye, Department of Crop, Soil, and Environmental Sciences University of Arkansas, Fayetteville, AR 72701. E-mail: firstname.lastname@example.org
Financial Disclosures/Conflicts of Interest: None reported.
Received September 4, 2015.
Accepted for publication December 7, 2015.