Seasonal CH4 and N2O emissions and plant growth characteristics of several cultivars in direct seeded rice systems

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 to determine to what extent choice of cultivar may have on GHG mitigation. We compared CH₄ and N₂O emissions, global warming potential (GWP = N₂O + CH₄), yield-scaled GWP (GWP_Y = GWP Mg^-1 grain), and plant growth characteristics of 8 cultivars within 4 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 differences in GWP and GWP_Y were observed, the consistency of some of the trends was variable 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, the lowest emitting cultivar had the highest yield. This highlights the potential for breeding high-yielding varieties with low GWP, the ideal scenario to achieve low GWP_Y due to simultaneously mitigating GHG emissions and improving global food security.