Emissões de gases de efeito estufa de cultivares de arroz sob irrigação por inundação contínua e intermitente

Abstract

Brazilian rice production comes predominantly from irrigated crops in Rio Grande do Sul, where the activity is considered to have a negative environmental impact, due to the high potential for greenhouse gas (GHG) emissions and water use. Several factors influence GHG emissions from rice fields, such as water management and cultivars. This work aimed to compare the GHG emission potential of rice cultivars under continuous and intermittent flood irrigation. The study was carried out under field conditions, in the 2019/2020 harvest, at the Experimental Station Terras Baixas of Embrapa Clima Temperado, in Capão do Leão-RS. The irrigated rice cultivars XP 113 (hybrid - Indian subspecies), BRS Pampa CL (Indian subspecies) and BRS 358 (Japanese subspecies) were evaluated in two irrigation systems (continuous and intermittent flooding) and two plant populations (150 and 300 plants m-2). The collections of air samples for the evaluation of methane (CH4) and nitrous oxide (N2O) emissions were performed using the closed static chamber method, with weekly or higher frequency. The total flows and emissions of CH4 and N2O from the soil were evaluated, as well as the productive performance and industrial yield of rice cultivars. The partial Global Warming Potential (pGWP) was also calculated, based on seasonal CH4 and N2O emissions and their respective global warming potentials (34 and 298), and the pGWP index on a grain yield scale (pGWP/GY). The main differences in CH4 fluxes were associated with the rice irrigation system, with higher emission peaks occurring in the period between booting stage and the beginning of flowering. For N2O, a characteristic emission temporal pattern was not observed due to the variation of the factors evaluated. Seasonal CH4 emissions were higher under continuous flood irrigation than intermittent flooding, with no effect of the irrigation system on total N2O emissions. The hybrid XP 113 provided lower total CH4 and pGWP emissions than the conventional cultivars BRS Pampa CL and BRS 358. The CH4 and pGWP emissions increased with the plant population. CH4 contributed to almost all of the pGWP associated with rice cultivation. The cultivars BRS Pampa CL and XP 113 provided higher grain yield than ‘BRS 358’. The intermittent flood irrigation system provided a lower pGWP/GY index, compared to continuous flooding, indicating that the flooding intermittency was effective in mitigating the GHG emissions and the pGWP of the rice crop. The hybrid XP 113 and ‘BRS Pampa CL’, under a smaller plant population, were superior to ‘BRS 358’ in terms of pGWP mitigation effectiveness in grain yield scale. Water management and the use of rice cultivars with less GHG emission potential are promising alternatives for mitigating pGWP in irrigated rice fields.