Methane Emissions among Hybrid Rice Cultivars in the MidSouthern United States

Abstract

Abstract. Rice (Oryza sativa L.) production systems have a greater global warming potential than upland row crops due to methane (CH4) emissions resulting from anaerobic conditions associated with flood-irrigated soils. Based on recent research indicating the potential for hybrid cultivars to mitigate CH4 emissions from rice, the objective of this study was to determine the influence of several commonly grown hybrid rice cultivars on CH4 fluxes and emissions from a silt-loam soil. Four cultivars were evaluated: the three hybrids CLXL729, CLXL745, and XL753 and the pure-line cultivar Roy J. Methane fluxes were determined by measuring changes in headspace CH4 concentrations over a period of 1 hour using 30-cm-inner-diameter polyvinyl chloride chambers. Only minor differences in CH4 fluxes occurred among the three hybrid cultivars, while the pure-line cultivar (Roy J) generally had greater (P < 0.05) fluxes. Peak CH4 fluxes occurred just after heading and were greater (P < 0.05) from Roy J (7.9 mg CH4-C m -2 h -1) than from the three hybrid cultivars, which did not differ and averaged 5.1 mg CH4-C m -2 h -1. Seasonal CH4 emissions were greater (P < 0.05) from Roy J (74.8 kg CH4-C ha -1 season -1 ) than from CLXL729, XL753, and CLXL745, which did not differ, and averaged 55.3, 53.0, and 48.9 kg CH4-C ha -1 season -1, respectively. Results of this study indicate the use of common hybrid cultivars may have potential for mitigation of CH4 emissions from rice production on silt-loam soils in the mid-southern United States.Keywords: Methane emissions, rice cultivar, hybrid rice, methane mitigation IntroductionRice (Oryza sativa L.) is the world's only major row crop that substantially contributes to global methane (CH 4 ) emissions. While most crops are grown under aerated soil conditions and act as net sinks for atmospheric CH 4 , the majority of rice throughout the globe is produced in flooded fields [1] and acts as a net source of CH 4 into the atmosphere. The anoxic conditions resulting from flooded soils lead to the production and release of CH 4 , a greenhouse gas with a global warming potential (GWP) 25 times stronger than carbon dioxide (CO 2 ) [2]. Due to the production of CH 4 , rice cultivation has been estimated to have a GWP 2.7 and 5.7 times stronger than the production of maize (Zea mays L.) and wheat (Triticum aestivum L.), respectively, with 90% of the GWP of rice systems attributed to CH 4 [3,4]. It has been estimated, on a global scale, that approximately half of all anthropogenic CH 4 emissions to the atmosphere are a direct result of agricultural activities [5,6] and that 22% of those agricultural CH 4 emissions occur due to rice cultivation [7]. Arkansas is the leading rice-producing state in the US, representing over 49% of harvested area in 2014 and resulting in an estimated 39% of total CH 4 emissions from rice cultivation in the US in 2014 [8].Methane emissions from a rice cultivation system are governed by the magnitude and balance between the two microbial processes of methanogenesis, the prod...

Socio-Technical Changes for Sustainable Rice Production: Rice Husk Amendment, Conservation Irrigation, and System Changes

“…Higher hybrid grain yield is also a benefit when considering net water usage and GHG changes on a peryield basis (Pittelkow et al, 2013;Brodt et al, 2014;Zhao et al, 2019). Hybrid varieties have also decreased both yieldand area-scaled CH 4 emissions relative to pure-line varieties, with suggested mechanisms including changed soil microbial activity and root exudation (Ma et al, 2010;Smartt et al, 2018). Genetic approaches are also used to generate low-CH 4 rice through the altered allocation of photosynthates to aboveground biomass rather than roots (Su et al, 2015;Kim et al, 2018).…”