As someone who raises livestock, I’m always interested in sourcing low-cost feed alternatives. Duckweed has been gaining a lot of attention in the farming community, owing to its ease of cultivation and the growing proof of its usefulness as a high-protein feed supplement.
Duckweed packs crude protein of 35 to 43 percent, fiber of 5 to 15 percent, polyunsaturated fat of 5 percent, and a host of trace minerals, calcium and Vitamins A and B. Its protein content is said to be equal to that of dried soybean meal. Not limited only to ducks, duckweed is fed to swine, chicken, cattle, sheep, goats, rabbits and farmed fish in many developing countries, with very positive results.
Duckweed is probably the smallest but fastest-growing plant there is. Grown in ideal conditions, it can double its weight in just 16-48 hours. Farmers who grow feed crops have found duckweed to be much more productive than soybean in terms of protein per surface area. It can produce 5-8 tons of dry matter for every acre per year, while soybeans produce less than a ton per acre each year depending on species, nutrient supply in the water, climate and environmental conditions.
Common duckweed, or lemna minor, grows in thick blanket-like mats on fresh or brackish still waters such as ponds, lagoons, swamps and slow-moving streams, especially those containing high amounts of nutrients like nitrogen and phosphorous. That’s why it’s often found in wastewater coming from residential areas, crop farms, hog and poultry operations, cattle feedlots, slaughterhouses and food processing plants, where effluent, excess fertilizers and slurry abound.
According to a study by the UN’s Food and Agriculture Organization (FAO), duckweed acts as a nutrient sink — absorbing primarily nitrogen, phosphorus, calcium, sodium, potassium, magnesium, carbon and chloride from waste matter. Depending on the water source, duckweed may be used as an animal feed or fertilizer. It may have to be decontaminated, though, prior to feeding to animals if there is a presence of heavy metals, as these are also consumed by the duckweed .
Duckweed can provide all the protein needs of tilapia and carp — which is why it works great for aquaponics . It can either be fed fresh as the solitary feed, but a combination of 50 percent dried duckweed and commercial pellets or other feed components produces much better results. Duckweed can be grown separately and then given to the fish, or grown in the same pond or container. Other aquatic animals that benefit from fresh duckweed are catfish, snakehead, silver barb, milkfish, jade perch and crayfish.
For livestock, duckweed is best given dry. It is highly recommended for small-scale integrated farming operations that include fish, pigs, chickens, quails, rabbits and ducks. For poultry, dehydrated duckweed can replace up to 40 percent of conventional feeds of laying hens and older broilers. Feeding trials in Peru have demonstrated that duckweed can substitute for the soybean meal for layers and broilers. Duckweed-fed layers  produced more eggs of the same or higher quality as control birds fed the formulated diets.
Duckweed is particularly noted for its high concentrations of K and P pigments, particularly carotene and xanthophylls — valued in poultry operations as these impart color to chicken skin and egg yolks.
For pigs, very little research has been done but a 30 percent dried duckweed diet was given to hogs in Vietnam and it resulted in high-nutrient digestibility.
But the best thing about duckweed is that it is also edible for humans. Duckweed resembles in taste to watercress or spinach. The wolffia genus has traditionally played a role in Asian cuisine, where it is used as a nutritious vegetable by the Thai, Burmese and Laotians. Duckweed can be mixed into soups and salad, or used in sandwiches as a substitute for alfalfa, lettuce, watercress or spinach.
Duckweed is found all around the world. It survives in extreme temperatures except deserts and perennially frozen regions. It thrives best in tropical and subtropical zones, but can grow anywhere with temperatures between 63 degrees and 86 degrees F (or water temperatures between 42 and 91 degrees F). Some species tolerate winters by sinking and laying dormant at the bottom of the water, only to resurface during warmer weather when normal growth can resume. Depending on species, duckweed thrives in ph levels 5 to 9, but likes the 6.5 to 7.5 range best.
FARMING, INDUSTRIAL USE AND PROCESSING
Duckweed needs to be carefully managed, as it is notorious for invasiveness. It can take over a small pond in a matter of weeks if left unchecked. Once a colony covers a pond’s entire surface, it can block sunlight and deplete the oxygen underneath, suffocating fish and other submerged plant life. Duckweed should be harvested frequently, preferably daily.
Some natural, non-chemical measures you can use to prevent duckweed overgrowth are:
- Raking and netting it often.
- Aerating, or possibly putting a water fountain which creates some movement in the water surface.
- Shading, which can be done by planting on the south side of the pond.
- Placing in the pond weed-eating water birds such as ducks, coots and moorhens, as well as herbivorous and omnivorous fish like tilapia, carp and silver barb
- Growing water lilies, lotuses and other plants with wide, floating leaves
Since duckweed contains up to 90-95 percent water, it is bulky and highly perishable when harvested. Collecting and dehydrating it on a large scale can be very cumbersome, time-consuming and expensive. The technology for desiccating duckweed on a massive scale has not yet been developed, so we can’t expect it to be commercially available in powder or pellet form anytime soon. For now, natural methods like sun-drying or drying in the shade with fans is more feasible for homesteaders and small farmers like you and me.
Have you ever used duckweed? What tips do you have? Share them in the section below: