Role and Applications of Azolla in Organic Agriculture

Azolla in Organic Farming

History of Using Azolla in Farming

In recent years, the supply of organic fertilizers has been a decisive factor in organic production, and one of the primary challenges in organic fertilization is finding reliable sources of organic nitrogen. In practice, we can use processed animal-based nitrogen. However, from an ecological perspective, this may not be a sustainable solution. Therefore, we need to find more sustainable alternatives. Using Azolla as fertilizer—providing a source of organic nitrogen—is a sustainable and effective solution because Azolla synthesizes nitrogen from the atmosphere for its own use through symbiosis with cyanobacteria in its leaves. If properly applied, Azolla plays an enormous role with extensive applications in organic agriculture.

_What is Azolla?_

Azolla (also known as mosquito fern or water fern, scientific name Azolla sp.) is an aquatic fern living in symbiosis with the nitrogen-fixing cyanobacterium Anabaena azollae. Azolla was first described in 1883 by the French naturalist Jean-Baptiste Lamarck. In Vietnam, during the 1960s production campaigns to rebuild the country, Azolla was one of the most widely promoted green manure plants and appeared across nearly all rural regions. Azolla ranges in length from 1 to 2.5 cm, with a main axis branching into secondary stems, all bearing small alternating leaves, along with branched roots and abscission layers that allow branches to detach and develop into independent plants. This is also Azolla's primary mode of reproduction.

_Figure 1: Azolla A( a: green A. filiculoides, b: red A. filiculoides), B ( a: red A. pinnata, b: red A. pinnata)_

_( Nham Tran 2020)_

The Role of Azolla in Organic Agriculture

Nitrogen is an essential macronutrient for plant growth. Although 78% of the atmosphere is free nitrogen, most plants cannot utilize it directly because they can only absorb nitrogen in the forms of nitrate (NO3-) and ammonium (NH4+). Through remarkable evolutionary development, Azolla possesses the unique ability to fix atmospheric nitrogen for its own needs thanks to its symbiotic relationship with cyanobacteria. As Azolla decomposes, it supplies an abundant source of nitrogen for other plants to absorb. According to research, cultivating Azolla requires no fertilizer application (Pereira et al. 2011, Nham Tran 2021), yet 1 hectare of cultivated Azolla can provide 1,100 kg of bioavailable nitrogen per year for crops.

Applications of Azolla in Organic Agriculture

1. Organic Fertilizer:

In recent years, as ecological concerns have come to the forefront, people have sought natural fertilizer sources to replace synthetic chemicals. Abundant natural macronutrient sources include potassium in banana stems, wood ash, and Mexican sunflower; nitrogen readily available from leguminous plants with symbiotic root nodules; and a significant nitrogen source in Azolla that should not be overlooked. Azolla is an outstanding organic fertilizer approved for organic farming. It easily replaces synthetic nitrogen, and crucially, allows farmers to remain self-reliant. Cultivation techniques are simple, with high capacity to fix atmospheric nitrogen and accumulate it in vegetative biomass. Cultivating and utilizing Azolla is thus an ideal practice for sustainable, efficient organic production.

2. Animal Feed

Azolla has a high crude protein content of 25–30% on a dry weight basis, with an amino acid profile comparable to soybean meal (Nham Tran 2020, 2021). Notably, its Ca, P, K, Mn, and Zn contents are all elevated. The manganese content in dried Azolla meal is significantly higher than that of other forage plants, leading to extensive research on Azolla as feed for various livestock and aquaculture species including goats, pigs, rabbits, chickens, ducks, shrimp, and fish. According to the scientific journal of the National Institute of Animal Science, one kilogram of fresh Azolla provides a nutritional value equivalent to 0.05–0.07 feed units (FU). Thus, one hectare of cultivated Azolla per season can yield 6,000–9,000 FU. Clearly, using fresh Azolla to feed pigs and ducks provides considerable economic benefits, especially for breeding sows.

A research report by Srinivas Kumar (2012) replacing 25% of total dietary protein with dried Azolla in male buffalo rations, along with studies replacing up to 50% with Azolla for calves and buffaloes (Indira et al. 2009), showed no adverse side effects on livestock. However, negative effects were reported when more than 20% Azolla meal was used to substitute total protein for goats (Samanta & Tamang 1995). Furthermore, feeding Azolla to cattle has been shown to improve milk yield (Chatterjee et al. 2013; Gowda et al. 2015; Mathur, Sharma & Choudhary 2013), and its use in rabbit feed has also been documented (Ramesh et al. 2011). Studies on fish and shrimp feed show that Azolla can replace 10–30% of protein without adverse effects (Radhakrishnan et al. 2014; Sudaryono 2011). Remarkably, Azolla can substitute for 100% of soybean meal protein for giant tiger prawn due to its nutritional similarity.

Therefore, it can be confidently stated that in addition to serving as an effective organic fertilizer, Azolla is also an excellent source of organic livestock and aquaculture feed—a promising alternative in the development of sustainable organic agriculture.