Fast-growing cattails sequester phosphorus. Harvesting them might be good for the environment, and better yet — it might be good for your bottom line
Harvesting cattails from the ditches, low spots and sloughs on your farm, could one day lower your fertilizer and energy costs. At least that’s the aim of a research study in Manitoba that’s focused on reducing the nutrient loading to Lake Winnipeg.
The major study is being conducted at Netley-Libau Marsh by the International Institute for Sustainable Development (IISD), the University of Manitoba and Ducks Unlimited Canada.
The study includes a project to evaluate cost effective ways to harvest cattails at the marsh and develop feasible end uses for the biomass and its by-products.
Cattails and phosphorus
Cattails produce a lot of plant material (biomass) throughout the growing season and as they do so, they absorb huge amounts of phosphorus. That phosphorus is released as the plants die or decompose, and eventually ends up in waterways — spring snow melt or rainfall carries the phosphorus along with it.
Harvesting cattails prevents that phosphorus from being released, helping to reduce nutrient loading into lakes and rivers.
Timing of the cattail harvest is important. Harvesting in late summer or early fall ensures that maximum amounts of biomass — and nutrient — are removed, while maintaining habitat for nesting wildfowl and other wildlife during the spring season. Cattails are extremely resilient and because harvesting opens the residue left behind to sunlight, vigorous plant regrowth will begin very early in the spring.
Once the cattails have been harvested there are opportunities to use the biomass to produce bio-energy and recover phosphorus to be re-used as fertilizer. Harvested cattails can be compressed into pellets and cubes for use in bio-energy heating systems that could potentially reduce on-farm heating costs. The Rock Lake Hutterite Colony near Grosse Isle, Manitoba is evaluating the use of unprocessed cattail biomass in its carbonizer burner system, in association with Manitoba Hydro.
The ash, called biochar, that remains after cattail biomass has been burned for energy is high in phosphorus and could be recycled as a slow-release fertilizer. The research being done by IISD and the U of M has shown that harvesting cattail biomass can remove 20 to 60 kilograms of phosphorus per hectare per year. “You can get 15 to 20 pounds per acre of phosphorus intercepted by harvesting cattails,” says Richard Grosshans of IISD. “Cattails are a very efficient phosphorus recycler.”
Harvesting cattails may bring some on-farm savings.
As an example, if a farmer were able to replace just 15 pounds of synthetic phosphorus fertilizer with biochar on an average wheat crop requiring 35 pounds per acre of phosphorus at a price of $0.49/lb., the savings would be $7.35 an acre.
There are also ecological benefits. Decreasing phosphorus loading into water bodies such as Lake Winnipeg decreases the potential for algae growth that negatively affects water quality. The vegetation also helps to slow down water flows and prevent erosion, as well as providing wildlife habitat. Studies have shown that if just five per cent of the agricultural land base of Manitoba were used to grow and harvest cattails it would intercept all of the phosphorus which now ends up in Lake Winnipeg.
Research into cattails’ ability to sequester carbon has demonstrated that they can sequester significant metric tonnes of carbon per hectare annually. This raises the possibility, as carbon markets develop globally, for farmers to benefit from carbon credits, not only by sequestration but also through the burning of cattail biomass for on-farm energy use, which could be sold as offsets for greenhouse gas emissions.
The potential exists, once the technology fully advances, to use cattail and other biomass for advanced bio-fuels like ethanol and for bio-fibres and bio-plastics, giving new opportunities for farmers to add value to their marginal and conservation land areas. †