Organic Rice Management Effects on Greenhouse Gas Emissions in Southeast Texas.

Increased demand for organic rice (Oryza sativa L.) has incentivized producer conversion from conventional to organically-managed rice production in the U.S. Little is known on the impacts of organic management practices on emissions of greenhouse gases (GHG) from rice fields. Improved management strategies could increase yield while simultaneously minimize environmental impacts. Field experiments were conducted at the Texas A&M AgriLife Research and Extension Center at Beaumont, Texas to assess and compare emissions of CO₂, CH₄, and N₂O from different organically managed rice production scenarios. During the first growing season (May – July), impacts of rice variety (Presidio, Clearfield XL723, and Tesanai), nitrogen source (Rhizogen and Nature Safe), and nitrogen application rate (0, 150, and 210 kg N ha^-1) on greenhouse gas (GHG) emissions were evaluated within three different fallow systems [ryegrass (Lolium multiflorum L.), clover (Trifolium repens L.), and weedy fallow]. Following the initial harvest, the impacts of N application rate and residue management (with or without straw returned) on GHG emissions were evaluated on a ratoon crop from September to November 2013. Finally, the impacts of winter cover crop on GHG emissions were evaluated from February to March 2014. Nitrogen application rate and rice variety had little impact on GHG emissions during the first year of this study. Organic N source had a significant impact on CH₄ emissions, where greater CH₄ emissions were observed from Rhizogen application compared to Nature Safe. During the ratoon crop, significantly more CO₂ was lost from plots where rice straw was returned compared to those without, but residue return had little impact on CH₄ emissions. In the winter, the greatest CO₂ emissions were observed in clover followed by ryegrass and then weedy fallow. This work provided important preliminary information on GHG emissions from organic rice production and will continue as an ongoing effort to identify management practices which maximize rice yield while simultaneously minimizing GHG emissions.