Azolla Fertilizer as an Alternative Organic Nitrogen Source for Malabar Spinach Production

The spread of organic farming has led to the need for identifying alternative sources of high-quality organic fertilizer. Azolla is a genus of floating aquatic ferns which has high nitrogen and organic matter content due to its fast growth and symbiotic relationship with nitrogen-fixing bacteria (Anabaena-azollae). However, little research has been done on the use of Azolla as an organic fertilizer for vegetable production. The study evaluated the effects of different levels of Azolla fertilizer on the growth and yield of Malabar spinach (Basella alba). The experiment included 6 treatments: Without application – as a control (T1); 1 ton ha^-1 soybean meal (T2); 16 tons ha^-1 cow manure (T3); 12 tons ha^-1 Azolla fertilizer (T4); 16 tons ha^-1 Azolla fertilizer (T5); and 20 tons ha^-1 Azolla fertilizer (T6). The results showed that the application of Azolla fertilizer significantly increased shoot length, number of leaves, leaf size, dry matter, leaf area index (LAI), and SPAD of Malabar spinach compared to the control or cow manure. The application of Azolla fertilizer at the rates of 12, 16, and 20 tons ha^-1 significantly increased the yield of Malabar spinach by 150, 192, and 205%, respectively, compared to the control; and by 37, 60, and 67%, respectively, compared to the cow manure treatment. Yields and parameters of harvested vegetables were the highest in treatments with 16 to 20 tons ha^-1 Azolla fertilizer. The results suggest that Azolla fertilizer can be used as an alternative organic nitrogen source in organic vegetable production.