Research developed by Embrapa and partners in the last ten years have shown good results in GHG mitigation in irrigated rice cultivated in the Brazilian South. Replacing continuous for intermittent flood irrigation is a feature that has mitigation potential above 70%. Other practices such as crop rotation, no-till farming, early tilling and nitrogen fertilization contribute to slowing the pace of global warming. These are some of science's responses to combine sustainability with high yield in rice crops in the South. The research informs breeding programs and public policy for the sector. Research developed by Embrapa Temperate Agriculture and educational and research institutions in southern Brazil in the last ten years has contributed to the mitigation of greenhouse gas (GHG) emissions in rice production. Several management practices have been implemented and adapted to lowland farming conditions in the Pampa biome with the aim of achieving carbon balance and contributing to increase water use efficiency, diversify the production system and identify rice genotypes that most adapt to climate change. The focus has been on irrigated rice cropping in Rio Grande do Sul, which accounts for over 87% of the country’s total methane emissions in the cultivation of the cereal, on top of a high water requirement. The most relevant practices include alternative water management systems for rice cultivation. Intermittent flooding and sprinkler irrigation, which replaces continuous flooding, has the potential to mitigate greenhouse gas emissions by over 70% and saves water. The use of nitrogen fertilizers for irrigated rice, based on the use of controlled-release fertilizers instead of traditional soluble sources, can reduce nitrous oxide and ammonia emissions from rice plantations. Ammonia emission factors from different sources of nitrogen in irrigated rice cultivation in southern Brazil are significantly lower than the reference indices proposed by the Intergovernmental Panel on Climate Change (IPCC), which is 10%. Another relevant research finding refers to crop diversification, i.e. the introduction of dryland crops like soybeans (pictured below), corn, sorghum, and forage plants in rotation with the irrigated rice, which significantly mitigates rice monoculture's potential for global warming. One of the practices resulting from the research that is already fully integrated into the production system is the adjustment of soil and mulch management for irrigated rice. Early tilling in the fall, in succession to the rice harvest, and rotation with soybeans reduce the annual global warming potential in the lowlands by more than five times. In addition, production systems that incorporate dryland crop rotations established in no-till farming and improved pastures, associated with rotational grazing, emit less methane, with a higher potential for soil carbon accumulation, and are thus recommended as environmentally sustainable alternatives to the lowland environment. Diversification of lowland production: soybean cultivated in rice area. Photo: Walkyria Scivittaro Directions for breeding programs and public policy The existing RD&I have been guiding rice breeding and genetic improvement programs towards the development of new varieties that not only have high grain yield and quality, but also gather resistance and tolerance to biotic and abiotic factors, nutritional quality and a lower potential for GHG emissions. They have also informed the elaboration of public policy aimed at environmental sustainability and minimizing the impact of agriculture on climate change. In that sense, it is worth nothing the inclusion of research results in the third and fourth editions of the National Inventory of Anthropogenic Emissions by Sources and Removals, specifically in the sector report “Methane Emissions from Rice Cultivation”. In both editions, for the state of Rio Grande do Sul, the estimated methane emissions from rice cultivation were calculated based on local factors, replacing the data proposed by the IPCC used in previous versions, allowing for a more realistic and favorable estimate of national emissions concerning irrigated rice farming. Measurement of GHG emissions in irrigated rice plantation. Photo: Walkyria Scivittaro GHG emissions in rice crops Researcher Walkyria Scivittaro, who coordinates studies on greenhouse gas emissions in irrigated rice farming at Embrapa, observes there is growing global demand for cereals, staple foods for the human population, which are produced in about 160 million hectares, roughly 11% of the world’s cultivated land. Although rice production is essential to humankind's food security, it has a potential negative impact on the environment, since the crop has a high water requirement, demands vast flooded areas and is associated with greenhouse gas emissions into the atmosphere. “To meet the demand for rice, which should grow about 20% over the next two decades, it is necessary to increase both the cultivated area and the crop yield. Both alternatives can intensify environmental impact in terms of the release of greenhouse gases into the atmosphere, especially methane and nitrous oxide,” she explains. IPCC data show that at a global level, rice production contributes to 30% and 11% of methane and nitrous oxide emissions, respectively. According to data from the Fourth National Inventory (2021), although Brazil is the largest producer of rice outside the Asian continent, methane emissions are less expressive (about 2% of the total). This can be explained by the area under irrigated cultivation, which totals less than 1.4 million hectares and is much smaller than that of the major grain-producing countries, located in Asia. Nevertheless, records by the Ministry of Science, Technology and Innovations (MCTI) points to irrigated rice cultivation in the South of Brazil, especially the state of Rio Grande do Sul, as relevant to the calculation of methane emissions from agriculture, as it accounts for over 87% of national emissions associated with producing the cereal. “The rice sector in Rio Grande do Sul is highly targeted by society from an environmental point of view, especially in terms of reducing greenhouse gas emissions and the high water requirement. Therefore, it is essential to invest in research, development and innovation measures to ensure the production required by the market with sustainability", Scivittaro explains. The irrigated share in domestic rice production A survey on Brazilian grain harvest made available by the National Food Supply Company (Conab) found that most of the Brazilian rice production comes from irrigated plantations in Rio Grande do Sul, which even though they account for less than 2% of the national area where the cereal is cultivated, provides over 70% of the national cereal production. Santa Catarina is another state that traditionally produces irrigated rice. More recently, Tocantins also increased the cultivated area with irrigated rice. The three states combined account for almost all of the national irrigated rice farming. While on the one hand the area with irrigated rice in Brazil has remained constant, but with increasing yields over the years that ensure domestic supply; on the other hand, the area with dryland rice production, which is traditionally developed in agricultural frontier areas, has been decreasing year after year, making room for more profitable crops, such as soybeans and corn. The retrospective statistics of national rice production reflect such trends. In 1990, the area cultivated with dryland rice in the country was close to 3.1 million hectares (74% of the total); then in 2021, dryland cultivation represented 23% of the total area (less than 0.4 million hectares), while the irrigation system totaled 1.3 million hectares (77% of the total). “Such data not only demonstrate the importance of rice production in Rio Grande do Sul for domestic grain supply and food security, but also the need and urgency of research efforts so that production is sustainably conducted and contributes to the achievement of Brazil’s GHG emission reduction targets pledged upon signing the Paris Climate Agreement, which aims to strengthen the global response to the threat of climate change and strengthen the ability of countries to deal with the effects of such changes", the researcher states. For her, it is clear that rotation of rice with dryland crops is highly beneficial to lowland production systems in Rio Grande do Sul, not only because it reduces GHG emissions from the irrigated rice crops, but also because it allows diversification of production in the property, nutrient cycling, and integrated pest management, especially weed control. On the other hand, the introduction of dryland crops in rotation with irrigated rice in the lowlands generally is limited by technical aspects, especially stress caused by excess water, due to poor soil drainage, and also due to water deficit, which is common in the region during the summer. Thus, the success of lowland crop diversification depends on the adoption of additional water management practices, such as soil softening and groove-ridge technology, which have been revolutionizing the production of grains, forage and winter cereals in this environment,” Scivittaro concludes.