Rice Cultivar Effects on Methane Fluxes and Emissions from Drill-Seeded, Delayed-Flood Rice on a Silt-Loam Soil.

Rice (Oryza sativa L.) is the only major staple food crop grown under flooded and subsequently anaerobic soil conditions. Anaerobic and reduced soil conditions result in methane (CH₄) emissions from the soil resulting in a greater global warming potential as compared to upland crops. Rice production in the Mid-South has rapidly accepted hybrid cultivars, which now represent upwards of 40% of planted-rice area. The objective of this study was to compare multiple hybrid cultivars as well as a pure-line cultivar. The study was conducted on a DeWitt silt loam (fine, smectitic, thermic Typic Albaqualfs) at the Rice Research and Extension Center near Stuttgart, Arkansas. Four cultivars were selected for the study: CLXL729, CLXL745, Roy J, and XL753. Gas sampling was conducted using the chamber method where weekly samplings were conducted during the flooded portion and every one to two days following flood release. Minimal differences were measured between hybrid cultivars where the pure-line cultivar resulted in significantly greater fluxes, particularly in the latter portion of the season. Fluxes peaked following heading where the flux from Roy J (7.9 mg CH₄-C/m²/h) was greater than the three hybrid cultivars (mean = 5.1 mg CH₄-C/m²/h), which did not differ. Following flood release, a significant post-flood release pulse was measured on day four. Methane emissions for the growing season were greater from Roy J (74.8 kg CH₄-C/ha/season) than from CLXL729 (55.3 kg CH₄-C/ha/season), XL753 (53.0 kg CH₄-C/ha/season), and CLXL745 (48.9 kg CH₄-C/ha/season), which did not differ. Emissions in the current study were 27 to 42% of the United States Environmental Protection Agencies current factor. Thus, CH₄ emissions from Arkansas rice production may be overestimated by the current CH₄ emissions factor.