AWD towards carbon credits in rice cultivation

Pilot measurement of methane emissions

Amid the increasingly complex climate crisis, Viet Nam’s agricultural sector, and Ha Tinh in particular, faces urgent pressure to transition to greener, more sustainable, low-emission practices. The shift is part of efforts to implement the national project on low-emission crop production for 2025–2035, with a vision to 2050, approved by the MAE.

After initial success applying alternate wetting and drying irrigation during the 2025 spring crop in Thien Cam commune, the model has been expanded province-wide for the 2026 spring season. With around 80 percent of rice now heading, methane (CH₄) measurement in the fields carries not only scientific value but also opens the door to developing carbon credit documentation for rice cultivation.

A nearly 20-hectare consolidated field in Minh Vuong hamlet, Can Loc commune, is among the sites selected for methane sampling during the 2026 spring crop. The area is also implementing the alternate wetting and drying technique through a collaboration between the provincial agriculture department, the North Central Agricultural Science Institute, and Japan-based Green Carbon Inc.

To ensure reliable results, methane sampling follows strict protocols. Gas collection chambers are firmly installed at representative locations within experimental plots to reflect actual farming conditions, including planting density, water levels, and irrigation regimes.

During measurement, the chamber is sealed over the rice plants, creating a closed space where emissions from soil and crops accumulate over time. Technicians then use airtight syringes to extract approximately 50 milliliters of gas, which is stored in glass vials for preservation.

Each sample is carefully recorded with detailed information including sampling time, identification code, ambient temperature, water level, and crop growth indicators. Maintaining consistency in sample volume and conditions across measurements improves the accuracy of data comparison.

Alongside fields using alternate wetting and drying, methane levels are also measured in conventionally farmed plots that remain continuously flooded. These serve as control samples to evaluate the emission-reduction effectiveness of the new method.

Collected gas samples are then sent to laboratories for analysis. Based on changes in methane concentration over time within the chambers, specialists calculate emission levels for each field and convert them into carbon dioxide equivalents ,  a key metric in greenhouse gas accounting.

Healthier crops, lower emissions

Beyond measurement, the alternate wetting and drying model has demonstrated clear production benefits. Initial results show irrigation water use reduced by 30 to 40 percent compared to traditional methods. Nitrogen fertilizer use has also dropped by up to 30 percent, significantly lowering costs for farmers.

Rice plants under this model exhibit stronger growth. Root systems develop deeper and more robustly, improving plant stability and reducing lodging. Effective tillering rates increase, while pest and disease incidence decline. These factors contribute not only to higher yields but also to improved grain quality.

Allowing fields to dry naturally for certain periods reduces anaerobic conditions,  the environment in which methane-producing bacteria thrive. As a result, methane emissions from rice paddies are effectively curtailed.

According to Phan Van Huan, head of the Crop Production Division under Ha Tinh’s Sub-Department of Crop Production and Animal Husbandry, more than 4,000 hectares of rice across 15 communes and wards applied the alternate wetting and drying technique during the 2026 spring crop. Experimental sites were set up at three locations,  Thien Cam, Can Loc, and Duc Thinh,  with methane measurements taken from representative fields under different irrigation regimes.

“Reducing methane emissions delivers not only environmental benefits. If standardized and officially recognized, this model could enable farmers to generate additional income by selling carbon credits,  a form of ‘green asset’ with value on international markets,  while enhancing the global standing of Vietnamese agricultural products,” Huan said.