Assessment of greenhouse gas mitigation from rice cultivation using alternate wetting and drying and rice straw biochar in Thailand

Abstract

The mitigation of greenhouse gas (GHG) emissions and water usage optimization in rice cultivation is challenging for many agricultural countries, including Thailand, who have set goals of reaching net zero emissions and coping with droughts caused by climate change. Alternate wetting and drying (AWD) and biochar application are possible practices for achieving cleaner rice production through reduction of GHG emissions and water consumption. However, these methods’ potential varies by site, especially in areas with limited control of water levels. This study assessed the effects of AWD at different drying levels (10, 15, and 20 cm below the soil surface) and rice straw biochar on GHG emissions, yield production, water use, soil characteristics, and economic aspects. This study was conducted over two rice cultivation seasons: a major season in 2022 and a second season in 2023 at a field in Kalasin Province, northeastern Thailand. Using AWD and biochar reduced annual GHG emissions by 48.2% and 8.01%, respectively. Deeper drying levels of AWD showed greater mitigation potential than shallow levels. The combination of AWD and biochar had additional potential for GHG mitigation, however, this impact did not show statistical change as compared to their separate potentials. The adoption of AWD and biochar could also maintain the amount of rice yield compared to traditional practice. All levels of AWD saved irrigation water consumption by an average of 16.8% per season; the highest potential was observed in AWD at 10 cm below the soil surface. Biochar improved soil health after two seasons by enhancing soil pH and organic carbon sequestration. The combination of AWD and biochar did not additionally augment the capacity in water saving of AWD or soil improvement of biochar. The AWD water regime also did not increase net profits, while biochar decreased net profits due to the required investment in biochar production. Using AWD is a feasible way to mitigate GHG emissions and save water without affecting rice productivity and net profits in northeastern Thailand.