Mulch makeover

Morris, Minn. – Minnesota lamb producers are not sheepish about taking a good idea back to the drawing board.

Several years ago, AURI helped the Minnesota Lamb and Wool Producers Association test a new landscaping mulch made from low-quality wool. The fabric was effective in strawberry trials at the University of Minnesota. But it had to be manufactured out of state, pricing it out of the market.

Still, wool landscaping fabric had so many advantages that the association decided to give it another try. Now AURI is helping sheep producers test a cheaper mulch made in Minnesota from low-value “card wool,” a byproduct of textile manufacturing. The revised wool mulch could offer fruit growers an economical alternative to herbicides. And farmers could see “new opportunities for a value-added product,” says Al Doering, AURI technical services specialist in Waseca.

Effective, but expensive

The original wool mulch, tested from 1999 to 2001 at the West Central Research and Outreach Center in Morris, was made from low-quality wool worth 5 to 10 cents per pound. The wool was washed and processed into a soft, felt-like fabric, using a method known as needle punching.

During three seasons of strawberry trials, the single-ply wool mulch “nearly eliminated weeds from rows, promoted daughter-plant rooting and allowed maximum fruit yields,” the research report stated. Weed control was as good or better than with conventional herbicides, and wool mulch kept the soil around plants cool and moist, leading to more robust growth, says horticulturalist Steve Poppe, who managed the research trials.

Also, the wool fabric was easy to handle, Poppe said. It could be applied with the same machine used to install plastic mulch. But unlike plastic, which can be a disposal problem after harvest, wool mulch decomposed by the end of the second season, enriching the soil with nitrogen. Wool mulch delivered similar results in tomato and medicinal herb trials, Poppe says.

The disadvantage? Price.

The cost of collecting, washing and trucking wool to the nearest needle-punch plants in Ohio and Texas pushed the mulch price to about 42 cents per square foot. “That’s too high for commercial strawberry growers,” Poppe says, “though it may fit the home gardening market.” (See story on page 6, “Blanketing the garden.”)

Making it cheaper

Still, Minnesota sheep producers were not ready to give up on the idea, says Michael Sparby, AURI project director. “The benefits were so good, we asked, ‘How can we get the cost down?’”

Sparby and Doering had worked with a Floodwood, Minn., company that makes roadside erosion-control mats out of waste agricultural fibers, such as wood and coconut. They wondered if Mat, Inc.’s fiber-mat manufacturing process could be modified for wool fibers.

The company was willing to try.

The first attempt failed. “The wool fibers were too long,” Sparby says. “We needed a fiber of three-quarters of an inch or less. We were brainstorming all kinds of things – chopping the wool, pelletizing it.” It was Bob Padula of Montevideo, a sheep farmer and president of the Minnesota Lamb and Wool Producers Association, who suggested using the short fibers trimmed from wool blankets made at Faribault Woolen Mills.

“The fibers are about half an inch long,” Sparby says. There is a market for them, but “they are an extremely low-value product.” Landscaping mulch would be a new use for the fibers, Doering adds.

After several tries, Mat, Inc. came up with a wool mulch similar to the original needle-punch mat, but lighter weight and less dense. It was also much less expensive – about one-fifth the cost of the needle-punch mulch, Sparby says.

Poppe, the horticulturalist at the Morris experiment station, is also a commercial strawberry producer. He says a low-cost wool mulch would undoubtedly appeal to strawberry farmers and other specialty fruit and vegetable growers. “A lot of Upper Midwest growers … are trying to lower their reliance on herbicides,” he says.

Comparing wool and herbicides

In May, the reformulated wool mulch was installed in transplanted strawberry plots at the Morris experiment station. The two-year trials are comparing wool with conventional herbicides and hand weeding. As in the previous wool mulch experiments, the research will look at weed growth, strawberry plant vigor, number of rooted daughter plants, and fruit yield.

Weed control through the end of July 2004 was good, Poppe reports, even though the new wool mulch is thinner than the original version. More care was needed during installation to avoid tearing the mulch, he says, although it was easier to cut through for planting.

So far, he adds, the new wool mulch “is doing what it’s supposed to be doing, and it’s not breaking down yet. But we’ll know more after next year when we see the yields.”

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