Potentials of azolla-cyanobacteria symbiosis as a biofertilizer in lowland rice production systems: A review

The reliance on chemical fertilizers seriously undermines ecosystem safety, soil health, and the essential reserves of organic matter. In contrast, biofertilizer Azolla significantly enhances rice yield while promoting soil fertility over extended periods. This literature review employs the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) approach, offering valuable insights for policymakers and researchers regarding Azolla’s numerous advantages, potential limitations, and innovative applications as an environmentally friendly modification for rice production. Significant findings highlight Azolla's remarkable ability for effective nitrogen fixation, which can even surpass the symbiotic relationship typically found in legumes when conditions are favorable. Notably, it can produce an additional 30–120 kg of nitrogen per hectare, thereby significantly increasing overall rice yield. Acting as a green manure in wet soil, Azolla accelerates the process of nitrogen mineralization and skillfully regulates floodwater pH levels, which helps to reduce ammonia volatilization losses and enhances the efficiency of nitrogen fertilizers. Furthermore, it substantially improves the chemical and physical properties of the soil, greatly enhancing microbial activity and facilitating the release of essential cations such as sodium, calcium, and magnesium. This multifaceted process leads to increased soil nitrogen content, available phosphorus, exchangeable potassium, and total nitrogen, ultimately benefiting rice nitrogen uptake. Therefore, applying Azolla is strongly advocated as a beneficial practice for sustaining crop productivity, enriching soil fertility, and promoting overall environmental sustainability.