Developing azolla for sustainable rice cultivation in the Mekong Delta

Vietnam has a long history of cultivating Azolla. As early as the 11th–12th century, Nguyen Minh Khong, a royal preceptor under the Ly dynasty, introduced Azolla to La Mien village, La Van commune, Thai Binh province.

From 1975 to 1985, Azolla was widely cultivated in rice fields across the Red River Delta (Thai Binh, Hai Duong, Ha Nam, etc.), where it was used effectively as green manure. Farmers relied solely on farmyard manure and Azolla, without chemical fertilizers.

After 1979, however, the practice of cultivating Azolla gradually disappeared as chemical fertilizers became widely available and quickly embraced by farmers. Over more than 50 years of chemical fertilizer use and quantity-driven agricultural production, farmland has become degraded, soil fertility and health have declined, and crop quality has suffered.

Excessive herbicide and pesticide use has further damaged the environment, harmed farmers’ health, and weakened productivity. Ultimately, unless corrected, rice cultivation risks becoming a “culprit” of environmental damage. For this reason, agriculture must urgently transition toward greener practices, and Azolla has emerged as a species of strategic importance in this new phase.

Azolla exhibits a remarkable ability to absorb CO₂, surpassing many other natural ecosystems. Estimates suggest that Azolla can remove dozens of tonnes of CO₂ per hectare per year. Its ability to fix atmospheric nitrogen not only supports rapid growth but also reduces the need for synthetic fertilizers, thereby lowering CO₂ and N₂O emissions.

Long-term carbon storage methods, such as biochar production or anaerobic biomass burial, are essential for converting absorbed carbon into tradable credits.

Azolla grows far faster and sequesters significantly more CO₂ than grasslands or forests in the United Kingdom. One hectare of Azolla can absorb up to 30 tonnes of CO₂ annually, compared with just 1 tonne per hectare for grasslands and about 7 tonnes per hectare for forests (Ben Mozt et al., 2008). In rice cultivation, Azolla also reduces nitrogen (NH₃) loss by 25–40% (Paul et al., 1995).

Additionally, Azolla contributes to water treatment by lowering heavy metal concentrations and has been applied in industrial wastewater management in several countries (Sela et al., 1985).

Leading certification organizations such as Verra and Gold Standard already have methodologies related to biomass and agriculture. However, the development of specific methodologies for Azolla will be key to unlocking its full potential in the carbon market.

Today, Azolla is once again being reintroduced into rice fields in several localities. Thriving in diverse aquatic habitats such as ponds, canals, lakes, and slow-moving rivers, Azolla’s outstanding biological trait is its exceptionally high biomass productivity, thanks to photosynthesis rates superior to most C4 plants. This enables Azolla to accumulate large amounts of biomass in a short time, forming the basis of its powerful carbon sequestration capacity.

History provides natural evidence of Azolla’s capacity as a “miracle plant” for carbon capture. Even in nitrogen-poor waters, Azolla grows optimally due to its symbiotic relationship with Anabaena, a cyanobacterium capable of fixing nitrogen independently for itself and its host. This explains why Azolla can double its biomass within just a few days when inoculated with Anabaena.

This independent nitrogen fixation benefits agriculture and underpins Azolla’s role in climate change mitigation. It eliminates one of the key growth-limiting factors for plants and enables Azolla to function as a highly efficient carbon sink.

Sustainable rice cultivation is being urgently implemented in the Mekong Delta to reduce greenhouse gas emissions (N₂O, CH₄, CO₂), restore soil fertility and health, and enhance both the quality and global brand value of Vietnamese rice.

Binh Dien Fertilizer Joint Stock Company is a pioneering enterprise in reviving and developing Azolla in the region. Its leadership, scientific council, and R&D Department plan to build an industrial-scale production model using advanced technologies.

The company intends to cultivate Azolla on 1 hectare under an intensive high-tech model for maximum yield and efficiency, tailored to the hot microclimate of the Mekong Delta. In parallel, it will launch a combined rice–Azolla system across 30 hectares in the 2025–2026 winter–spring crop. By 2026–2027, the system will expand to 200 hectares, with a target of 300 hectares by 2030.

The model aims to cut nitrogen–phosphorus–potassium (NPK) fertilizer use by 40% and reduce pesticide applications. It will produce 20,000 kilograms of fresh Azolla to support organic cultivation on 30 hectares of rice in the 2025 - 2026 winter–spring crop, with rice yields expected to increase by 20% compared to control plots without Azolla.

Thus, Azolla will soon re-emerge in the Mekong Delta, laying the foundation for sustainable rice cultivation and significant reductions in greenhouse gas emissions.