Date of Graduation

5-2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Crop, Soil & Environmental Sciences (PhD)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Richard Norman

Committee Member

Kristofor Brye

Second Committee Member

Michelle Evans-White

Third Committee Member

Edward Gbur

Fourth Committee Member

Nathan Slaton

Keywords

Ammonia Volatilization, Methane, Rice, Trace Gases

Abstract

The Environmental Protection Agency (EPA) currently uses a single methane (CH4) emissions factor of 160 kg CH4-C ha-1 for a primary rice (Oryza sativa L.) crop. The emissions factor is based on studies that do not adequately represent current management practices in Arkansas. Another concern is pre-flood fertilizer nitrogen (N) management, as the common N source, urea, is prone to loss via ammonia (NH3) volatilization. Thus, the objective of this research was to investigate trace gas emissions from rice on a silt-loam soil, including CH4 emissions as influenced by nitrogen (N) fertilization (i.e., optimal N and no N) in 2011, and previous crop [i.e., soybean (Glycine max L.) or rice] and cultivar (i.e., semi-dwarf, standard-stature, and hybrid) in 2012, and to assess the impact on grain yield of ammonia (NH3) volatilization from preflood urea application with and without the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT). A chamber-based method was used to measure methane fluxes and linear interpolation and numerical integration between individual sample dates was performed to determine seasonal emissions. Ammonia volatilization was measured using semi-open static chambers. In 2011, no differences (P > 0.05) were measured in CH4 emissions due to N fertilization where mean annual emissions were 195 kg CH4-C ha-1. Methane emissions in 2012 were greater (P < 0.05) when rice was the previous crop (184 kg CH4-C ha-1) compared to when soybean was the previous crop (127 kg CH4-C ha-1), and emissions were greater from the semi-dwarf pure-line cultivar (169 kg CH4-C ha-1) and standard-stature pure-line cultivars (186 kg CH4-C ha-1), which did not differ, compared to the hybrid cultivar (111 kg CH4-C ha-1). Ammonia volatilization was reduced (P < 0.05) and grain yield increased when using NBPT compared to untreated urea. Methane results suggest the EPA's emissions factor potentially overestimates CH4 emissions in Arkansas, as 70% of rice production follows soybean and 50%

of production is from hybrid rice. Results also indicate NH3 volatilization can be reduced by the usage of NBPT. Thus, trace gas emissions measurements from rice will improve long-term sustainability assessments of rice.

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