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New Mexico State University

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Biosolid Compost Fights Disease in Greenhouse Experiment

ALBUQUERQUE -- One of the easiest ways to improve your garden soil is by adding compost. A recent New Mexico State University study shows that compost made from biosolids (sludge) and landscaping wood wastes also can act as a natural fungicide.

"In 1995, a biosolid compost we obtained from Albuquerque was effective in controlling some soilborne diseases in chile," said George Dickerson, horticulture specialist with NMSU's Cooperative Extension Service. "This spring, we successfully tested the same compost for Pythium control in greenhouse-grown snapdragons."

Dickerson worked with greenhouse cutflower grower Monica Parker, of Edgewood, on the project. He substituted the biosolid compost for all or part of the peat moss in her potting soil. The amended soil was planted with snapdragons, a plant very susceptible to the Pythium fungus.

"We found that pots in which either one-quarter or one-half of the peat moss was replaced with biosolid compost resulted in the least plant damage," Dickerson said. "Plants in the grower's pure peat moss mix were heavily infected with Pythium, while plants in the pure biosolid compost had extensive salt damage."

During the composting process, biosolid compost can reach 150 degrees. The compost is allowed to cool and cure for several weeks. While curing, various fungi help break down larger, wood-based materials.

"In theory, the fungi in the wood-based compost give it the fungicidal characteristics," Dickerson said. "When the compost is incorporated in the soil, these microorganisms seem to be better competitors for water and nutrients than soilborne pathogens like Pythium."

One problem with manure or biosolid composts is they often contain salts. Not all salts are bad, but in large quantities they can burn young plants.

"Biosolid composts have a lot of great characteristics that we need to explore," Dickerson said. "But because of the salt content, it's important for us to determine the best application rates for optimum results."