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

Kristofor R Brye,Alden D Smartt,Richard J Norman

doi:10.4236/jep.2017.89060

Abstract

Methane (CH4) emissions are known to differ between rice (Oryza sativa L.) cultivars, where CH4 emissions from pure-line cultivars are often greater than from hybrids. Numerous field studies have shown that CH4 emissions follow a diurnal pattern, typically reaching their maximum during afternoon hours. However, it is unknown whether cultivar affects CH4 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 CH4 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 CH4 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 CH4-C m-2· hr-1 from the clay soil and from 2 to 7 mg CH4-C m-2·hr-1 from the silt-loam soil. Hourly CH4 fluxes and estimated daily emissions differed among measurement times of day (P 4 flux or daily emissions for a given day differs by soil texture and rice growth stage, but conducting CH4 flux measurements around late morning to mid-day appear to be optimum to best capture the mean CH4 emissions for the day.

Highlights

Measurement time of day is important for attaining the most accurate estimations of seasonal and/or annual methane (CH4) emissions [1]
Results suggested that the optimum measurement time of day to capture either minimum, maximum, or average hourly CH4 flux or daily emissions for a given day differs by soil texture and rice growth stage, but conducting CH4 flux measurements around late morning to mid-day appear to be optimum to best capture the mean CH4 emissions for the day
Based on the results of this field study conducted among four location-growth stage combinations during the 2014 rice growing season from the direct-seeded, delayed-flood production system in eastern Arkansas, hourly CH4 fluxes and estimated daily emissions differed among measurement times of day for a given cultivar or averaged across cultivars

Summary

Introduction

Measurement time of day is important for attaining the most accurate estimations of seasonal and/or annual methane (CH4) emissions [1]. Temporally scaled CH4 emissions may be under- or over-estimated depending on the time of day in-field CH4 flux measurements are conducted. During the night and early morning have generally been reported as the times of day with the lowest CH4 fluxes/emissions [6] [7] [8] [11] [13]. Numerous studies have reported no significant difference in CH4 emissions between day and night [6] [14] [15]

Methods

Results

Conclusion