Produtividade de grãos, da água e emissão de gases de efeito estufa sob práticas alternativas de irrigação em arroz

Abstract

The lowland areas of the southern part of Rio Grande do Sul are predominantly cultivated with border irrigated rice in the continuous flooding system. This irrigation method is characterized by low water use efficiency and high greenhouse gas emissions. Given the current scenario of climate change and water scarcity, the seek for alternative irrigation methods and/or systems that are efficient in the water use, that promote high yield and quality of the grains produced, as well as provide a reduction in gas emissions greenhouse effect has been a constant challenge to research and the productive sector. In this sense, border irrigation methods in intermittent flooding and sprinkler systems emerge as alternatives to traditional flood irrigation, aiming to reduce water use and lessen environmental impact. Although these irrigation methods can promote a reduction in water use, plants can be affected by the reduction in water availability. When associated with conditions of high evapotranspiration demand, they can cause morphophysiological changes in rice plants, promoting a reduction in their growth and development, with effects on the yield and quality of the crop's grains. Thus, the present study aimed to evaluate the agronomic performance and morphophysiological modifications of rice varieties subjected to different irrigation methods and systems, as well as their influence on irrigation water productivity (Chapter I); evaluate yield components and grain quality of rice varieties subjected to irrigation methods and systems (Chapter II), as well as the influence of irrigation methods and systems on methane and nitrous oxide emissions, global warming partial potential and the relation with grain yield of irrigated rice varieties (Chapter III). For this, experiments were carried out in the 2019/20 and 2020/21 growing seasons in the lowlands didactic-experimental area at the Federal University of Santa Maria. As the main results obtained, it was verified that intermittent irrigation provides a reduction in the use of water without harming the productivity and quality of rice grains. However, due to the intensity of the intermittence used, the emission of methane and nitrous oxide were not affected, being the PAGp/PG similar to that verified by continuous irrigation. Sprinkler irrigation promotes reduced water use, however, with a reduction in shoot and root dry matter accumulation, nutrient accumulation, parameters related to photosynthesis, number of grains per panicle and grain yield. In addition, sprinkler irrigation had a higher percentage of opaque and plastered grains and reduced whole grain rice yield. As for the emission of greenhouse gases, the sprinkler provided a reduction in the emission of methane from the soil in rice cultivation, however, it increased the emissions of nitrous oxide. Variety IRGA 431 CL provides reduced water use and higher irrigation water productivity, without harming grain yield with lower percentage of opaque and plastered grains and higher whole grain rice yield than variety IRGA 424 RI. The fluxes and total emission of methane and nitrous oxide, as well as the partial global warming potential were not influenced by rice varieties, containing similar values of PAGp/PG.