Potencial da irrigação por inundação intermitente em mitigar as emissões de gases de efeito estufa de cultivares de arroz

Abstract

Irrigated rice cultivation is responsible for significant greenhouse gas (GHG) emissions, mainly methane (CH₄). This occurs mainly in crops that use the continuous flooding system, which keeps the soil saturated throughout almost the entire rice growing cycle. Flooding the soil creates ideal conditions for the activity of methanogenic microorganisms, which decompose organic matter in the soil, releasing CH4. Rice crops also contribute to the emission of other GHGs, such as carbon dioxide (CO₂) and nitrous oxide (N₂O), but in smaller quantities. The intermittent flood irrigation system, which alternates periods of flooded and drained soil during the rice growing cycle, can constitute a strategy to mitigate GHG emissions from rice crops, particularly CH4. This study was developed with the objective of evaluating the potential and intensity of GHG emissions from rice cultivars under continuous and intermittent flood irrigation. The study was carried out in the 2019/2020 to 2021/2022 agricultural harvests, in Planossolo, at the Terras Baixas Experimental Station of Embrapa Clima Temperado, in Capão do Leão, RS. Over the three harvests, four conventional irrigated rice cultivars (BRS Pampa CL, BRS A705, BRS Pampeira and BRS 358) and two hybrid cultivars (XP 113, XP 117) were evaluated. GHG emissions were measured by the closed static chamber method. Seasonal CH4 and N2O fluxes and emissions and the productive performance of irrigated rice were evaluated. The partial global warming potential (GWP) of the crop was also calculated, considering the global warming potentials of CH4 and N2O in relation to CO2, respectively 28 and 265, as well as the crop's emission intensity (GWP/RG), which relates GWP to grain yield (RG). The main differences in CH4 emissions were associated with the rice irrigation system, being higher under continuous flooding compared to intermittent flooding. The highest emission peaks occurred in the period between the booting and the beginning of rice flowering. Seasonal CH4 emissions and GWP were higher under continuous flooding irrigation compared to intermittent flooding, with no effect of the irrigation system on total N2O emissions. Irrigated rice cultivars differed in terms of CH4 and GWP emission potential, as well as in tolerance to water stress caused by intermittent irrigation. In general, cultivars that combine an early biological cycle and high production potential have a greater potential to mitigate GHG emissions and GWP. The intermittent flood irrigation system is a promising alternative to reduce GHG emissions and the global warming potential of rice crops in the lowlands of Rio Grande do Sul. However, the adoption of this technique requires careful management, considering the interaction between water management and nitrogen fertilization, avoiding substantial increases in N₂O emissions and stress due to water deficit and ensuring the sustainability of production.