Wool gathering for carbon sequestering

by Tamara Scully

The sheep industry has an excess of wool. Larger farms – and some smaller ones, particularly if they aggregate their wool via a wool pool – sell on the commodity market, directly to a wool mill or warehouse. Smaller farms often sell specialty fiber and wool products directly to the consumer, as a value-added product. But too much wool doesn’t make it to market.

Kimberly Hagan and Suzy Hodgson of the University of Vermont Extension’s Center for Sustainable Agriculture want to create new markets for this raw wool that was otherwise going to waste.

It can cost more to shear the sheep and transport the wool than the price raw wool commands. And not all raw wool is of a high quality, so even producers with a niche product market are left with quantities of lower quality raw wool. Raw wool of low quality has few marketing opportunities.

Many producers store their wool on the farm, with no better end use for what amounts to a by-product of raising sheep. Even if producers do find a market for the raw wool, processing it to meet the market’s requirements is another obstacle.

“Nearly all value-added products to be made with wool need scouring first,” Hagan explained. “Insulation, sound absorption wall material, tapestry, upholstery: it has to be scoured or moths will invade. They love dirty wool.”

That scouring step comes with significant costs. Scouring of wool requires large amounts of water. Because the wool contains lanolin, which is emulsified during the process, a grease trap is required to capture it for eventual disposal at the landfill. The water used becomes nutrient-laden, Hagan said, and requires handling similar to water from manure pits in order to avoid negatively impacting ground water quality.

There are smaller mills that will scour small batches of wool for producers, but their capacity is limited. Chargeurs Wool in South Carolina is a primary processor of larger wool quantities for East Coast farmers.

“Chargeurs can do 10,000 pounds of wool in a day, while most of these local mills will do 4,000 to 10,000 pounds in a year,” Hagan said, explaining that water quality regulations act to limit scouring capacity. “Setting up a large scale facility in the Northeast would be a very significant financial undertaking. I had imagined utilizing one of the vacant old mill buildings or factories around New England, and renovating for that purpose.”

With the cost of scouring wool a primary concern, the challenge of finding an end use for raw wool that otherwise would be wasted meant thinking creatively about how it could be utilized in its natural state.

Wool traits

Some notable properties of wool include its ability to absorb water in quantities above its own weight, and to give off heat while doing so. Wool will also retain its shape once any absorbed water is released.

Wool also doesn’t burn – it smolders. In Europe, wool upholstery, bedding and other household products don’t require chemical flame retardants, although they do in the U.S., Hagan said.

Wool’s ability to absorb and release water, as well as to insulate, makes it a good candidate for use on the farm. This natural product could potentially help protect plants from fluctuations in moisture level, or add warmth to cool soil and speed up production.

Wool’s NPK value is 9:0:2, making it a potential source of nitrogen, without adding any phosphorous to fields that might not need it. Because wool is 50% carbon by weight, the potential to sequester that carbon on the farm while providing fertility and water retaining abilities seemed promising, Hagan said.

But spreading wool by hand isn’t practical on anything but a small scale, and the wool takes a while to break down.

Wool, however, can be pelletized into small, dense packets. As an added benefit, nitrogen is released slowly when in pelletized form, eliminating runoff risks. Wool also meets requirements for certified organic use.

Farm trials

Three Vermont farm test sites utilized wool pellets (sourced from a pelletizer in Utah) during the 2019 growing season. Each farm grew broccoli in 100-foot side-by-side rows. Wool pellets were incorporated into the soil in one row, and the farm’s normal fertilizer used in the second. One farm also had a third row with no treatment.

The University of Vermont (UVM) farm has very sandy soil, while the other two farms feature heavier clay and clay loam type soils, Hagan said. Therefore, comparison between farms isn’t as important as comparisons to results on each individual farm.

At Golden Russet Farm, the wool pellets were hand-broadcasted, and tilled to four inches in depth. The broccoli receiving this treatment yielded a few pounds more per 100 square feet – 74.5 versus 72.3 – than their normal peanut meal fertilizer. They also grew a row with no fertilizer added, which yielded 68.3 pounds per 100 square feet. The broccoli treated with wool pellets was ready to harvest three days sooner than the rest.

At Shelburne Farms, the wool pellets were hand-broadcast and tilled in with the crown vetch cover crop to a depth of two inches. The broccoli treated with the wool pellets yielded the exact same amount – 154 pounds per 100 square feet – as that grown treated with their standard 5:3:2 fertilizer. No difference in maturation between the treatments was seen.

At UVM, the wool pellets were hand-broadcasted and tilled to two inches in depth. The wool pellets provided a much higher yield than their normal peanut meal side dressing fertilizer. The peanut meal’s yield was 19.5 pounds of broccoli per 100 square feet, while the wool pellets yielded 61.5 pounds. Peanut meal is the most commonly used side dressing fertilizer in the region, Hagan said.

“We theorize that the wool hung onto the moisture and the nutrients, making them available to plants as the season went on,” Hagan said of the results in UVM’s sandy soil. “The nutrients leached from all the heavy precipitation on the non-treatment row, and it also lacked moisture during the dry period.”

Looking ahead

The challenge now is to be able to pelletize the wool locally, and make it available for larger scale use in a pilot project. The cost of production of the wool pellets is still unknown, and fundraising – most likely with a crowdfunding component – will be necessary to launch the project.

“Right now we are just sitting tight to see how things go. Shearers are in a holding pattern, and the Vermont wool pool has delayed scheduling,” Hagan said, adding that funding is the biggest obstacle.

Some questions remain to be answered. How is the carbon in wool is being utilized? If wool pellets are tilled into the soil, does the carbon get added into the soil and sequestered?

“It seems to make sense, but really we don’t know,” Hagan said of carbon sequestration. “But the preliminary information is quite positive so we’ll keep moving forward.”

Further information on the project can be found at uvm.edu/extension/sustainableagriculture/vermont-wool-and-other-natural-fibers.

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