The effects of cultural practices on drill-seeded delayedflood rice (Oryza sativa L.) production on methane (CH 4 ) emissions are not well quantified. In Arkansas, rice is produced predominantly on loamy soils following soybean (Glycine max L.) as the previous crop, and hybrid rice has replaced a large percentage of pure-line cultivars in the past decade. Therefore, research was conducted during the 2012 growing season to assess the effects of previous crop (rice or soybean) and cultivar (standard-stature, semi-dwarf, and hybrid) on CH 4 emissions on a silt-loam soil. A 30-cm-diameter chamber-based method was used to determine fluxes during the 2012 growing season. When soybean was the previous crop, fluxes were generally lower (P < 0.05) until heading, after which all fluxes decreased until flood release. Seasonal emissions differed based on previous crop and cultivar (P < 0.05). Area-and yieldscaled growing season emissions from rice following soybean were less (127 kg CH 4 -C ha −1 ; 13.7 kg CH 4 -C (mg grain) −1 ) than when rice followed rice(184kgCH 4 -Cha −1 ;20.5kgCH 4 -C(mggrain) −1 ).Hybridriceemitted less (111 kg CH 4 -C ha −1 ; 11.1 kg CH 4 -C (mg grain) −1 ) than semi-dwarf (169 CH 4 -C ha −1 ; 18.3 kg CH 4 -C (mg grain) −1 ) or standard-stature rice (186 kg CH 4 -C ha −1 ; 21.9 kg CH 4 -C (mg grain) −1 ), which did not differ. Thus, results indicated decreased emissions when soybean was the previous crop and when the hybrid cultivar was grown. The incorporation of factors known to influence CH 4 emissions (i.e., previous crop, cultivar, and yield) will improve estimates of the carbon footprint of rice.

Due to anaerobic conditions that develop in soils under flooded-rice (Oryza sativaL.) production, along with the global extent of rice production, it is estimated that rice cultivation is responsible for 11% of global anthropogenic methane (CH4) emissions. In order to adequately estimate CH4emissions, it is important to include data representing the range of environmental, climatic, and cultural factors occurring in rice production, particularly from Arkansas, the leading rice-producing state in the US, and from clay soils. The objective of this study was to determine the effects of previous crop (i.e., rice or soybean (Glycine maxL.)) and cultivar (i.e., Cheniere (pure-line, semidwarf), CLXL745 (hybrid), and Taggart (pure-line, standard-stature)) on CH4fluxes and emissions from rice grown on a Sharkey clay (very-fine, smectitic, thermic Chromic Epiaquerts) in eastern Arkansas. Rice following rice as a previous crop generally had greater (p<0.01) fluxes than rice following soybean, resulting in growing season emissions (p<0.01) of 19.6 and 7.0 kg CH4-C ha−1, respectively. The resulting emissions from CLXL745 (10.2 kg CH4-C ha−1) were less (p=0.03) than those from Cheniere or Taggart (15.5 and 14.2 kg CH4-C ha−1, resp.), which did not differ. Results of this study indicate that common Arkansas practices, such as growing rice in rotation with soybean and planting hybrid cultivars, may result in reduced CH4emissions relative to continuous rice rotations and pure-line cultivars, respectively.

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