Changyoon Jeong, Jim Wang and Xi Zhang

Rice cultivation is critical to global food security, providing a staple food for more than half of the world's population. Most U.S. rice production areas are the Arkansas Grand Prairie, the Mississippi Delta area, the Sacramento Valley of California and the Gulf Coast, including Texas and southwest Louisiana. However, rice cultivation is water-intensive and can be significantly impacted by climate change. Implementing climate-smart practices in rice cultivation is vital for enhancing sustainability, reducing environmental impacts and ensuring food security in changing climatic conditions. Climate-smart rice cultivation aims to increase productivity in an environmentally and socially sustainable way, strengthen farmers' resilience to climate change, and reduce greenhouse gas emissions where possible. LSU AgCenter promotes climate-smart rice farming such as efficient water management, soil health practices with nutrient management, integrated pest management, utilizing climate data and modeling to support farmers in planting time and managing risk associated with climate variability, and recommends resilient rice varieties to climate stress.

Greenhouse gas emissions from rice production primarily come from methane (CH₄) released during flooded rice cultivation and nitrous oxide (N₂O) emissions associated with fertilizer application and organic matter decomposition. Mitigating these emissions is crucial for reducing the environmental footprint of rice farming. However, emissions vary, primarily reflecting the impact of management practices. In particular, continuous flooding of paddies stimulates CH₄ emissions, whereas the fertilizer nitrogen (N) application rate is the most crucial driver of N₂O emissions.

Cover crop cultivation in rice paddies can alter the decomposition dynamics of organic matter, leading to reduced methane emissions. Certain cover crops, such as legumes or grasses, can provide carbon inputs that stimulate microbial communities in the soil, promoting aerobic decomposition and reducing methane-producing anaerobic conditions. In addition, cover crop root exudates — the fluid emitted through the roots — can also influence soil microbial activity, leading to reduced CH₄ production. Cover crop management strategies, such as incorporating cover crop residues into the soil before flooding, can shorten the duration of anaerobic conditions during the rice-growing season, thereby reducing CH₄ emissions. Legume cover crops can fix atmospheric nitrogen, reducing the need for synthetic nitrogen fertilizers and consequently mitigating N₂O emissions associated with fertilizer application. The biomass produced by cover crops adds organic carbon to the soil, improving soil structure while helping decrease N₂O emissions by promoting aerobic conditions.

Water management in rice cultivation is essential for ensuring the sustainability and resilience of this vital crop in the face of global challenges. Through the adoption of improved cultivation techniques, the development of stress-tolerant rice varieties, and the implementation of integrated farming practices, it is possible to achieve higher productivity, enhanced environmental sustainability and improved livelihoods for rice farmers worldwide.

Traditional rice farming methods, such as continuous flooding, require large quantities of water and contribute to water scarcity in many regions (Figure 1a). Improved water management techniques are essential for making rice cultivation more sustainable and climate-smart. Alternate wetting and drying (AWD) water management is the most popular water-saving technology, which can not only significantly reduce water use by 15%-30% but also AWD decreased N₂O emissions by 12%-70%, which was attributed to optimizing field soil moisture during the application of fertilizer (Figure 1b).

Furrow-irrigated rice production also uses a controlled irrigation method that supplies water directly to the plant roots through furrows (Figure 1c). This method can significantly reduce water usage, making it a more sustainable option in water-scarce regions or under conditions where water conservation is essential. Furrow irrigation minimizes the time for the field to flood and lowers CH₄ emissions compared to flooded rice farming methods. Moreover, by optimizing fertilizer use and reducing runoff, furrow-irrigated rice can minimize nutrient leaching into water bodies, thus protecting aquatic ecosystems. While furrow-irrigated rice offers many advantages, its implementation faces challenges. These include the need for specific infrastructure (like leveled fields and the ability to control water delivery precisely), knowledge and training for farmers to manage the new system effectively, and initial investment costs.

Additional climate-smart practices in rice cultivation may include two more options. The first option is to use enhanced efficiency nitrogen fertilizer (EFNF) to mitigate N₂O emissions and NH₃ volatilization. The typical EFNF is urea or urea ammonium nitrate (UAN) treated with N stabilizers such as urease and nitrification inhibitors or urea coated with polymer. Researchers have found that applied N stabilizers extended the availability of applied N-fertilizer and reduced nitrate production, which is the predominant N₂O precursor under subtropical and tropical regions of the southern U.S. A second option is the application of biochar, a stable form of carbon-derived from biomass conversion under high temperatures with limited oxygen conditions to enhance soil fertility and mitigate greenhouse gas emissions. Biochar amendment was reported to enhance soil physical, chemical and biological properties by improving the soil structure, bulk density, porosity, water and nutrient retention, and hydraulic conductivity. Abundant oxygen- and nitrogen-containing functional groups and aromatic moieties, such as benzene-like properties, on biochar surface could alter the soil's cation- and anion-exchange capacities, improve nutrient retention in the solid phase and increase nutrient availability in the soil solution. Thus, biochar potentially acts as a slow-release fertilizer by infusing it with other nutrients and reducing inorganic N fertilizer, mitigating N₂O gas emission.

Currently, LSU AgCenter soil scientists are researching the optimization and implementation of these different climate-smart strategies and improving soil health parameters to ensure the management of continued and resilient rice production in Louisiana. Implementing these climate-smart strategies requires collaboration among farmers, researchers, policymakers, extension agents and other stakeholders. Supporting policies, incentives and investments are also necessary to facilitate adoption and scaling up these practices, ultimately contributing to more resilient, sustainable, and productive rice production systems in the face of climate change.

Changyoon Jeong is an associate professor at the LSU AgCenter Red River Research Station. Jim Wang is a professor in the AgCenter School of Plant, Environmental and Soil Sciences, and Xi Zhang is an assistant professor at the Red River Research Station.

This article appeared in the spring 2024 edition of Louisiana Agriculture.

Figure 1. Rice farming methods include several options for irrigation including:

a. Conventional flooded rice

b. Alternate wetting and drying

c. Furrow-irrigated rice. Rice planted in raised beds in furrow-irrigated cultivation reduces labor costs but is also vulnerable to weeds and insects.