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A Morelet's crocodile (Crocodylus moreletii) amid profuse Azolla fern.

A Morelet's crocodile (Crocodylus moreletii) amid profuse Azolla fern in Laguna Catemaco, in Los Tuxtlas Biosphere Reserve at the center of the Sierra de los Tuxtlas, Veracruz, Mexico.

Credit: Claudio Contreras/Nature Picture Library

Azolla Fern

Call to action:

Grow azolla to sequester carbon from the atmosphere, clean polluted waterways, and create regenerative animal feed, green manure, and biofuel.

The aquatic azolla fern is a wonder plant. It grows quickly on the surface of ponds and stores atmospheric carbon in its tissues; it can replace fossil fuel–intensive nitrogen fertilizers in agriculture and substitute for monoculture crops in animal feed; it can clean up heavy metals in wastewater; and it can be a regenerative source of biofuels. Azolla uniquely draws nitrogen directly from the air. When the mulched plant is introduced to soil, the nitrogen becomes available for use in agriculture or gardens. The nitrogen means azolla is packed with protein, making it a replacement for soybeans in animal feed. In rice paddies, azolla can double productivity, reduce disease-spreading mosquitoes, decrease methane emissions, and reduce water loss.

Action Items

Individuals

Learn about azolla and its many benefits. There are seven species of azolla across every continent except Antarctica. They grow as free-floating aquatic plants on the surface of ponds, ditches, and wetlands, often forming a thick mat. In addition to absorbing carbon, all azolla species share a unique ability to make nitrogen fertilizer from the air with the help of Anabaena azollae, a cyanobacteria that is dependent on azolla for its survival. The benefits of azolla include:

Support the use of azolla and spread the word about its benefits. One of the best ways to support azolla is to find growers making use of it and buying their products. Another is to support groups who spread the word about how azolla can be incorporated into agricultural and other activities.

  • The Japanese farmer Takao Furuno has made it his life’s mission to spread the word on how rice can be grown without artificial fertilizers or pesticides by integrating ducks, fish, and azolla into production. He has reached more than seventy-five thousand farmers across Asia. If you live in Japan, you can purchase his products.
  • The Azolla Foundation operates the most comprehensive website of azolla resources and has compiled numerous success stories. It’s for-profit sister entity, Azolla Biosystems Ltd. is a UK-based company looking to develop a number of commercial azolla products and tools.
  • Online retailers sell fresh azolla for cultivation in ponds or aquariums. One in India also sells powdered azolla as a soil additive.
  • The Climate Foundation has a project growing azolla in the geothermal waters of Nevada.

Grow and eat azolla. Azolla can be used around the house for fertilizing plants or a garden. It is safe to add to a salad or omelet (just make sure there are no snails where it is grown as they can spread certain kinds of parasites). Fresh azolla has been described as having a “crisp texture” and a taste “earthy and reminiscent of a forest.” It composts in about ten days. All you need is some sunlight, a bit of soil, and a container like a bucket.

  • A number of guides to growing azolla at home are available online.
  • Azolla can be purchased online, including on Etsy, but it is probably best to source it locally from a farm or wetland, to avoid spreading a nonnative species. Azolla may be sold at your local garden supply store, particularly if they stock aquatic plants for backyard ponds.
  • One azolla grower reported that azolla even helps keep the bees visiting their garden from drowning, by giving them a platform to land on when going for a drink.

Groups

Farmers

Learn more about azolla in agriculture. Azolla has been used to boost crops since AD 540 when the Chinese scholar Jia Si Xue wrote about rice farmers incorporating it into their paddies in his book The Art of Feeding People.

  • Azolla makes its own nitrogen fertilizer at a rate roughly equivalent to 1,600 pounds of urea fertilizer (one of the most common nitrogen fertilizers used in industrial agriculture) per acre per year. It can boost rice harvests while decreasing nitrogen fertilizer demand by 20 to 30 percent. It absorbs phosphorous and potassium and other micronutrients that would likely wash away.
  • Azolla can help suppress common weeds and reduce mosquito populations that spread disease, including malaria, dengue fever, Zika, chikungunya, and yellow fever.
  • Azolla can be used in many forms of permaculture, a type of land management that often involves the creation of swales and retention ponds, which are ideal settings for growing azolla. In return, the azolla helps the ponds by decreasing evaporation while also providing a self-renewing food source for fish or ducks or harvestable feed for livestock.
  • Azolla can play an essential role in a number of specific permaculture strategies, most famously the rice-duck-loach system pioneered by Takao Furuno. The azolla fills the space between the rice plants and provides the staple diet for ducks that are then able to control populations of invasive snails.
  • Helpingfarm in India provides instructions on cultivating azolla and using it as cattle feed.

Incorporate azolla into farm operations. A wide variety of crops grow better with azolla green manure, and many farm animals can eat azolla as feed.

Document azolla initiatives on video or with social media. Sharing successes and solutions helps smooth the way for others, particularly with regional challenges related to climate, geography, and local pests.

  • Farmers from Indonesia to Lebanon to the Philippines have recorded their experiences growing azolla, creating valuable resources for others.
  • The Azolla Foundation has compiled a variety of online resources to help farmers get started.

Scientists

Establish azolla extension centers. Research on the optimal use of azolla for local contexts could yield major dividends.

  • Scientists in Vietnam identified thirty strains of their local azolla species and screened them for tolerances for heat, cold, acidity, and salinity.
  • The International Rice Research Institute in the Philippines has assembled the world’s largest collection of azolla strains (over five hundred) and have tested them in the lab and fields for use in rice cultivation.
  • The Cooperative Extension Service of the University of Hawai’i Manoa helped develop and popularize a system for growing azolla as a green manure in flooded taro fields.

Conduct research on gaps in our understanding of azolla. Most research on azolla has focused on its utility as a green manure, as an animal feed, or in phytoremediation, the use of plants to remove harmful compounds or chemicals from the environment. One area in need of investigation is how azolla could be paired with waste processing at concentrated animal feed lots or sewage treatment plants. Other areas:

  • More research is also needed to understand the scalability of azolla as a biofuel feedstock. Azolla mitigates many of the problems associated with biofuels, but it’s not clear it can be grown at large scale. However, it could play a valuable role if it were possible to create small batches of azolla biofuels, allowing small permaculture operations to become even more independent of fossil fuel infrastructure.
  • Azolla may have once radically cooled the planet by spreading across the Arctic Ocean. Could it be grown safely in large reservoirs, lakes, or even river systems polluted with excessive nutrient runoff? Are there offshore regions like in the Gulf of Mexico or the Amazon where freshwater lenses could allow intentionally seeded azolla blooms to transport carbon from the atmosphere down to the seafloor as they die?

Companies

Use azolla inputs for supplements, animal agriculture, fertilizer, cosmetics, and biofuels. There’s a wide variety of products that could potentially be derived from azolla.

Incorporate azolla into wastewater management and bioremediation operations. Azolla can act like a sponge for a number of compounds often need to be removed from wastewater.

  • Azolla will readily take up phosphorus, which is present in dangerous quantities in many areas because of agricultural runoff and detergent use. And even though it can fix its own nitrogen from the air, azolla will also soak up nitrogen from secondary sewage that can otherwise cause harmful algal blooms and offshore dead zones.
  • Azolla can absorb a variety of heavy metals, including nickel, cadmium, and lead.
  • In a study in China, researchers found that azolla was able to remediate tailings from a uranium mine. The azolla brought iron, copper, zinc, and lead concentrations in line with drinking water standards, and reduced uranium concentrations to safe levels.
  • A study from India found azolla was useful for phytoremediation of fly ash, a by-product of burning pulverized coal in power-generating plants.

Governance

Create transparent rules for farming azolla. There are extensive regulatory processes in place for marketing new agricultural products in most countries, especially when it comes to new animal feeds. Clear, easy-to-follow rules need to be established to help farmers know what they can and can’t do with azolla.

  • Regulatory bodies, such as the U.S. Department of Agriculture, need to create a streamlined process for bringing new low-carbon or carbon-negative feeds to market.
  • Some azolla species have shown an ability to become invasive when introduced outside their native range, so it is important to establish clear rules about what species can be used in what regions.

Fund azolla research. The easiest way for scientists to start new investigations on azolla is with government grants. Much of what we know about azolla came from research supported by government, for example, this study funded through a grant from the National Key Research and Development Program of China.

  • Many of the most influential studies on azolla came from agricultural research centers like the International Rice Research Institute, which has been supported by the governments of the Philippines, India, Japan, the UK, China, the U.S., and Germany.

Support phytoremediation using azolla. There are many public sites where azolla could be used to clean wastewater, sewage, mine tailings, or fly ash.

  • Government support or mandates could be used to resolve pollution issues with azolla, while simultaneously drawing carbon down out of the atmosphere.
  • Depending on the pollutants involved, the azolla grown in this way could either be used to create useful products, or the carbon embedded in them could be stored underground alongside the pollutants, sequestering it permanently.

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