Methane Emissions from Drill-Seeded, Delayed-Flood Rice Production on a Silt-Loam Soil in Arkansas

Abstract

Rice ( L.) production is unique among staple food crops because the majority of the growing season typically occurs under flooded-soil conditions. Flooding the soil leads to anaerobic conditions, which are a precursor to methane (CH) production. However, no known research has investigated CH emissions from the drill-seeded, delayed-flood rice production system common in Arkansas, the leading rice-producing state in the United States. Therefore, research was conducted in 2011 to determine the effects of vegetation (rice and bare soil), chamber location (in- and between-rice rows), and nitrogen (N) fertilization (optimal and no N) on CH emissions from a silt-loam soil. Methane fluxes measured weekly from flooding until flood release were affected by vegetation, chamber location, and sample date ( < 0.05). In-row CH fluxes were <0.7 mg CH-C m h until 20 d after flooding (DAF) and <1.0 mg CH-C m h from between-row and bare soil until 41 DAF and were unaffected by fertilization over time. The largest weekly measured CH flux (31.9 mg CH-C m h) was observed from in-row rice at 41 DAF. Post-flood-release CH fluxes were affected by vegetation, fertilization, chamber placement, and sample date ( < 0.05) and accounted for approximately 3 to 7% of the season-long CH emissions. Methane emissions averaged 195 kg CH-C ha per growing season and were unaffected by fertilization. Direct measurement of CH emissions from drill-seeded, delayed-flood rice grown on a silt-loam soil will improve the accuracy of assessments of the carbon footprint and long-term sustainability of rice.

Methane Emissions among Hybrid Rice Cultivars in the MidSouthern United States

“…The proportion of CH 4 emitted following flood release in this study, however, was similar to emissions ranging from 10.5% from CLXL745 to 16% from a semi-dwarf, pure-line cultivar observed by Rogers et al [30]. Post-flood CH 4 release has been observed in numerous previous studies ranging from 3 to 20% of total area-scaled emissions [30,32,51,54,56,70,74]. While the magnitude of post-flood-release CH 4 emissions differs among various treatments, it has become apparent that CH 4 has the potential to accumulate in saturated soils and be released as the soil dries and macropores become accessible for gas transport.…”

“…The seasonal pattern of CH 4 emissions increasing once the flood is applied, peaking near heading, then declining prior to flood release has been observed in numerous previous studies [30,32,49,51,53,59,60,61,62] and suggests that root exudates increase during vegetative growth providing substrate for methanogenesis and decrease again during grain fill as resources are translocated to the filling grains. Research conducted by Denier van der Gon et al [63] indicated that CH 4 emissions are related to allocation of photosynthetically derived C between roots and grains and that decreasing translocation of C to grains (i.e., removing florets prior to grain fill) causes an increase in C translocation to roots and an increase in CH 4 emissions.…”

“…Gas sampling throughout the study occurred between 0800 and 1000 hours, similar to previous studies [30,32,48,49,51,52,53], in order to prevent excessive heating within the chambers during sampling. Gas samples for flux measurements occurred on approximately weekly intervals at 7,14,21,28,35,43,49,56,63,71, and 77 days after flooding (DAF) for the flooded duration of the study.…”

“…Gas samples for flux measurements occurred on approximately weekly intervals at 7,14,21,28,35,43,49,56,63,71, and 77 days after flooding (DAF) for the flooded duration of the study. Sampling intensity was increased after flood release to 80, 82, 83, 84, and 85 DAF [i.e., 2, 4, 5, 6, and 7 days after flood release (DAFR)] in an attempt to adequately quantify a post-flood-release pulse of CH4 that has commonly been observed in previous studies [32,48,49,51,54,55,56].…”

Cultivar and Previous Crop Effects on Methane Emissions From Drill-Seeded, Delayed-Flood Rice Production on a Silt-Loam Soil

“…Chamber headspace volume was determined for every chamber at each gas sampling by measuring the height of the chamber above the flood water. Weekly sampling was conducted mid morning, similar to previous studies (Adviento-Borbe et al, 2013;Rogers et al, 2013;Shang et al, 2011). Gas samples were collected between 800 and 1000 h (Shang et al, 2011;Rogers et al, 2013) based on mean daily soil temperatures of the study region (Rogers et al, 2013) to minimize biases associated with soil temperature fluctuations, which are often correlated with diurnal variations in CH 4 fluxes (Denier van der Gon and van Breemen, 1993;Schütz et al, 1989).…”