Date of Graduation

5-2015

Document Type

Thesis

Degree Name

Master of Science in Crop, Soil & Environmental Sciences (MS)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Brye, Kristofor R.

Committee Member

Norman, Richard J.

Second Committee Member

Hardke, Jarrod T.

Third Committee Member

Roberts, Trenton L.

Fourth Committee Member

Gbur, Edward E. Jr.

Keywords

Biological sciences; Earth sciences; Cultivar; Emissions; Methane; Previous crop; Rice

Abstract

Due to the production of methane (CH4) under flooded-soil conditions, rice (Oryza sativa L.) cultivation is a major contributor to agricultural CH4 emissions. Studies examining CH4 emissions from rice have only recently been initiated in Arkansas and no data have been collected from rice produced on clay soils in Arkansas. Therefore, research was conducted in 2012 and 2013 at the Northeast Research and Extension Center in Keiser, Arkansas to examine the factors affecting CH4 emissions from rice produced on a Sharkey clay (very-fine, smectitic, thermic Chromic Epiaquerts). The objectives of this study were to determine: 1) the effect of vegetation (i.e., no vegetation, low vegetation, and high vegetation) on CH4 fluxes and season-long emissions from a clay soil, 2) the effect of chamber size (i.e., 15.2-cm and 30-cm inner diameter) on measurements of CH4 fluxes and emissions, and 3) the impact of previous crop [rice or soybean (Glycine max L.)] and cultivar (Cheniere, Taggart, and CLXL745) on CH4 fluxes and emissions. Total season-long emissions in 2012 were greatest in the high vegetation treatment (P < 0.01), amounting to 35.6 kg CH4-C ha-1, compared to 1.8 and 8.96 kg CH4-C ha-1 in the no vegetation and low vegetation treatments, respectively. Methane fluxes or season-long emissions did not differ between the two chamber sizes evaluated. Season-long emissions in 2013 were 64% lower (P < 0.01) following soybean than following rice, amounting to 7.0 and 19.6 kg CH4-C ha-1, respectively. Season-long emissions were 31% lower (P = 0.03) from the hybrid cultivar (CLXL745) than from the pure-line, semi-dwarf cultivar (Cheniere) or the pure-line, standard-stature cultivar (Taggart), which totaled 10.2, 15.5, and 14.2 kg CH4-C ha-1, respectively. The low emissions measured in this study, coupled with the magnitude of Arkansas rice production and extent of production on clay and clay-loam soils (> 40%) in Arkansas, indicates that CH4 emissions from mid-southern U.S. rice cultivation may be substantially overestimated. Further research on mid-southern CH4 emissions from various locations and cultural practices will be important to more accurately assess current greenhouse gas emissions from rice production and to mitigate potential negative impacts on the environment.

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