|Simmonds, Maegan - University Of California|
|Anders, Merle - University Of Arkansas|
|Adviento-borbe, Maria - University Of California|
|Van Kessel, Chris - University Of California|
|Linquist, Bruce - University Of California|
Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/2014
Publication Date: 1/8/2015
Citation: Simmonds, M.B., Anders, M., Adviento-Borbe, M.A., Van Kessel, C., Mcclung, A.M., Linquist, B.A. 2015. Seasonal methane and nitrous oxide emissions of several rice cultivars in direct-seeded systems. Journal of Environmental Quality. 44:103-114.
Interpretive Summary: Greenhouse gases like methane and nitrous oxide, when released into the atmosphere, have the ability to increase global temperatures. Agricultural activities are associated with significant greenhouse gas emissions. Rice is generally produced in flooded fields as a means of weed control but this production system results in oxygen depleted soils during the growing season. Under these conditions, methane producing soil bacteria can grow and the methane is released into the atmosphere by translocation through the rice plant’s root system and stems, and out through the leaves. Global rice production is considered a major contributor to methane emissions and global warming. Although different production practices including fertilizer application, water management, and tillage methods can be implemented to reduce greenhouse gas emissions, this study was conducted to determine if rice cultivars can also play a role in mitigation of emissions. Eight commercial rice varieties were evaluated, some being tested in California and others in Arkansas. Replicated field studies were conducted and methane and nitrous oxide emissions were determined for each variety over the course of the growing season. It was found that methane accounted for over 90 percent of the greenhouse gas emissions with nitrous oxide playing a much smaller role. Although there were differences among the cultivars for greenhouse gas emissions, the differences were not consistent over field locations or years. However, rice varieties were identified that had low emissions and high grain yield. This indicates the potential for being able to both reduce emissions from rice production fields without compromising grain yield of this staple crop for much of the world.
Technical Abstract: Understanding cultivar effects on field greenhouse gas (GHG) emissions in rice (Oryza sativa L.) systems is needed to improve the accuracy of predictive models used for estimating GHG emissions and determine to what extent choice of cultivar may have on GHG mitigation. We compared methane (CH4) and nitrous oxide (N2O) emissions, global warming potential (GWP = N2O + CH4), yield-scaled GWP (GWPY = GWP Mg-1 grain), and plant growth characteristics of eight cultivars within four study sites in California and Arkansas. Seasonal CH4 emissions differed between cultivars by a factor of 2.1 and 1.3 at one California and one Arkansas site, respectively. Nitrous oxide emissions were negligible, comprised <10% of GWP, and were not different among cultivars. When sites and cultivars were pooled, and data were normalized to site averages, there was a positive correlation (r = 0.33) between root biomass at heading and seasonal CH4 emissions, but no correlation with shoot biomass at heading, or grain or straw biomass at maturity. Although significant differences in GWP and GWPY were observed among cultivars, these were not consistent across sites indicating the importance of the genotype x environment interaction. While no high-yielding and low CH4-emitting cultivars were identified at the California sites, among the Southern varieties tested at the Arkansas site in the second year, the lowest emitting cultivar had the highest yield, demonstrating the potential for breeding high-yielding varieties with low GWP, the ideal scenario to achieve low GWPY due to simultaneously mitigating GHG emissions and improving global food security.