Diurnal Methane Fluxes as Affected by Cultivar from Direct-Seeded, Delayed-Flood Rice Production

Abstract

Methane (CH 4 ) emissions are known to differ between rice ( Oryza sativa L.) cultivars, where CH 4 emissions from pure-line cultivars are often greater than from hybrids. Numerous field studies have shown that CH 4 emissions follow a diurnal pattern, typically reaching their maximum during afternoon hours. However, it is unknown whether cultivar affects CH 4 fluxes/emissions at various measurement times of day or how those cultivar effects may differ spatially across soil textures and temporally throughout the rice growing season. The objective of this field study was to evaluate the effects of time of day (300, 800, 1200, 1800, and 2300 hours) and cultivar (one hybrid and one pure-line) on CH 4 fluxes before and after heading from a silt-loam and clay soil in a direct-seeded, delayed-flood rice production system. Enclosed headspace chambers, 30 cm in diameter, were used for CH 4 gas sampling on 22 July and 19 August at a silt-loam site and on 29 July and 26 August, 2014 at a clay-soil site in the Lower Mississippi River delta region of eastern Arkansas. Methane fluxes measured pre- and post-heading ranged from 0.7 to 2.2 mg CH 4 -C m -2 · hr -1 from the clay soil and from 2 to 7 mg CH 4 -C m -2 ·hr -1 from the silt-loam soil. Hourly CH 4 fluxes and estimated daily emissions differed among measurement times of day (P < 0.05) for a given cultivar or averaged across cultivars and differed between cultivars (P < 0.05) from the silt-loam soil, but not the clay soil. Results suggested that the optimum measurement time of day to capture either minimum, maximum, or average hourly CH 4 flux or daily emissions for a given day differs by soil texture and rice growth stage, but conducting CH 4 flux measurements around late morning to mid-day appear to be optimum to best capture the mean CH 4 emissions for the day.