Date of Graduation

5-2018

Document Type

Thesis

Degree Name

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

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor

Kristofor R. Brye

Committee Member

Richard J. Norman

Second Committee Member

Cammy Drost Willett

Third Committee Member

Michelle Evans-White

Keywords

Rice, Arkansas, nitrous oxide, water management

Abstract

Rice (Oryza sativa L.) is a common crop grown in Arkansas under flooded-soil conditions. The saturated to nearly saturated soil makes rice production an ideal environment for the production of potent greenhouse gases, such as nitrous oxide (N2O). The objectives of this study were to i) evaluate the impact of water management practice (full-season-flood and intermittent-flood) and cultivar (pure-line and hybrid) on N2O fluxes, season-long N2O emissions, and global warming potential (GWP; 2016) and ii) evaluate the impact of tillage practice [conventional tillage and no-tillage (NT)] and type of urea fertilizer [ N-(n-butyl) thiosphosphoric triamide (NBPT)-coated and non-coated urea] on N2O fluxes, season-long N2O emissions and GWP (2017). For both objectives, rice was grown in a direct-seeded, delayedflood production system. Gas samples were collected from enclosed chambers at 20-min intervals for 1 hr approximately weekly between flood establishment and 4 to 7 days after endof- season flood release. In 2016, both N2O fluxes and season-long N2O emissions were unaffected (P > 0.1) by water management or cultivar. However, season-long N2O emissions ranged from 0.38 to 0.84 kg N2O-N ha-1 season-1 from the full-season-flood/hybrid and intermittent-flood/hybrid treatment combinations, respectively. The GWP differed (P < 0.003) between cultivars, where the hybrid (XL753; 2272 kg CO2 eq. ha-1 season-1) had a substantially lower GWP than the pure-line cultivar (LaKast; 4473 kg CO2 eq. ha-1 season-1). In 2017, both N2O fluxes and season-long N2O emissions ranged from 0.27 and 0.50 kg N2O-N ha-1 season-1 from NT/NPBT-coated urea and NT/non-coated urea, respectively, but were unaffected (P > 0.1) by tillage practice or type of urea fertilizer. The NT/non-coated-urea combination (2204 CO2 eq. ha-1 season-1) had the numerically largest GWP, but GWP was unaffected (P > 0.05) by tillage or fertilizer type. There are limited N2O emissions studies that have been conducted in rice production in the US, therefore, it is important to quantify and evaluate N2O emissions from common rice production practices (full-season-flood and conventional tillage) and their alternatives (intermittent-flood and no-tillage) to estimate the environmental impacts of these practices when rice producers are considering a conversion to more sustainable practices.

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