Date of Graduation

12-2021

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

Wood, Lisa S.

Second Committee Member

Lessner, Daniel J.

Third Committee Member

Henry, Christopher G.

Keywords

Greenhouse gases; Nitrous oxide; Rice; Soil

Abstract

As the number one rice (Oryza sativa)-producing state in the United States, Arkansas also ranks fourth as the largest user of groundwater. Recently, due to the development of drought- resistant hybrid cultivars, the furrow-irrigated rice production system has become an increasingly popular alternative to traditional flood-irrigated production with respect to conserving groundwater and maintaining yield. However, other environmental parameters, like greenhouse gas emissions, specifically nitrous oxide (N2O), have yet to be evaluated under furrow-irrigated rice. The objectives of this study were to i) evaluate the effects of site position (i.e., up-, mid-, and down-slope) and tillage treatment [i.e., conventional tillage (CT) and no-tillage NT)] on N2O fluxes and season-long emissions from a furrow-irrigated rice production system on a silt-loam soil in east-central Arkansas, and ii) to evaluate the effects of nitrogen (N)-fertilization amount and timing [i.e., 100% of the early season optimum N rate plus one split application (OPOS), 50% of the early season optimum N rate plus two split applications (HOPTS), 100% of the early season plus two split applications (OPTS), and an unamended control (UC)] on N2O fluxes and season-long emissions in a greenhouse trial simulating a furrow-irrigated rice production system. Gas collection occurred weekly over the 2018 and 2019 rice growing seasons for the field study and during 2020 growing season for the greenhouse trial. In 2018, N2O emissions differed (P < 0.1) among site positions and differed between tillage treatments, while 2019 emissions differed (P < 0.1) only between tillage treatments. Nitrous oxide emissions in 2018 were greatest at the down-slope position (3.34 kg N2O ha-1 season-1) compared to both the mid- (2.78 kg N2O ha-1 season-1) and up-slope (2.74 kg N2O ha-1 season-1) positions, which did not differ. For both growing seasons, CT produced greater (P < 0.1) N2O emissions than NT, where mean annual emissions from CT were 3.15 and 2.58 kg N2O ha-1 season-1 for the 2018 and 2019 seasons, respectively. In 2020, N2O fluxes differed among fertilizer-N treatments over time (P < 0.01), yet there was no consistent trend between mid-season fertilizer-N application timing and the timing of peak N2O fluxes. Nitrous oxide emissions numerically ranged from 0.42 kg N2O ha-1 season-1 from the UC to 0.65 kg N2O ha-1 season-1 from the OPOS treatment, but unlike fluxes, did not differ (P = 0.60) among N-fertilizer treatments. Results of these studies highlight the importance of soil management practices and water regimes in regulating N2O production and release from rice fields. The evaluation of N2O fluxes and emissions from furrow-irrigated rice is essential to understanding the environmental impact of furrow-irrigation as an alternative water management scheme for rice production.

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