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New Compost Shows Mixed Results Controlling Vegetable Diseases

Farmers may be able to suppress certain types of foliar diseases of snap beans and cucumbers by using composted paper mill residuals, according to researchers at the University of Wisconsin-Madison.

However, soil scientist Leslie Cooperband, and plant pathologist Dorith Rotenberg caution that using composted paper mill residuals may also increase the severity of potato early blight and potato early dying diseases. Rotenberg presented their research at the 2002 Wisconsin Fertilizer, Aglime and Pest Management Conference in Madison Jan. 17.

The research on disease suppression is part of a larger project to examine two, 3-year crop rotations including potatoes, snap beans and cucumbers. “We”re trying to determine if additions of organic matter affect soil quality and crop disease-and, by extension, crop yield, quality and overall profitability,” explains Cooperband. “We are also evaluating the environmental benefits of adding organic matter to sandy soils: reducing nitrate and pesticide leaching and wind erosion, for example.”

Although the project is still underway, Cooperband is not sitting back and waiting for six years before she assesses the results, “We’re using the results from our research to make recommendations on how to improve soil quality and reduce pesticide use through natural disease suppression.”

Potatoes and vegetables are big business for Wisconsin farmers: Wisconsin is the nation”s leading producer of vegetables and ranks third in potato production, according to the Wisconsin Potato and Vegetable Growers Association. The WPVGA, along with the University of Wisconsin and the World Wildlife Fund, is working on a green label initiative for Wisconsin potatoes. “A ”green label” means that farmers use sustainable practices and reduce pesticide use,” says Cooperband. “Our results so far indicate that paper mill residue compost is effective in lowering the incidence of some diseases, including potato storage rot, bean pod brown spot and cucumber angular leaf spot.”

Paper mill residuals are the by-products of the papermaking process, a mixture of the short fibers that do not stick to the paper press, processing water and binding agents. This primary sludge is transported to a wastewater treatment center, where microbes break down the particles and form secondary sludge. Nutrients such as nitrogen and phosphorus are added to help the microbes break down the primary sludge, so the secondary sludge has good nutrient value and a high level of organic matter.

Cooperband”s research compares experimental plots with no amendment, plots spread with raw paper mill residuals, and plots spread with two types of paper mill residuals: one composted alone and one composted with bark. In addition to the mixed effects on disease, she found that the paper mill residuals compost increases the availability of water in soil, thereby increasing the ability of crops to use nutrients and water efficiently.

At present, paper mill residuals compost is not available commercially, but there are several paper mills that spread raw residuals on farmers” fields. Paper mill landspreading programs charge farmers a small, per-acre fee to subsidize the cost of providing the sludge.

However, not everyone is enthusiastic about using paper mill residuals in vegetable production. “Some processors won”t accept potatoes from these fields, because they are concerned that the sludge contains metals, dioxins and PCBs,” says Cooperband. “The reality is that paper mills have modified the paper-making process such that metal and organic toxin concentrations are practically undetectable. Both the public and processors need to be educated about this, so we are documenting soil and crop contamination levels. That way, the processors and the general public know that the food is safe.”