Agronomist Richard Fox (left) and research technologist Rex Rosario are measuring levels of nitrates that leach from spent mushroom substrate in order to help mushroom growers find ways to reduce nutrient runoff.

The mushroom industry needs to dispose of more than 500,000 tons of used mushroom compost each year. Called spent mushroom substrate (SMS), this nutrient-rich mixture can be used as a soil amendment, growing media, or in mine reclamation and wetland construction. "But mushroom producers are located in one area, and the nearby businesses that can use spent mushroom substrate can only take so much of it," Needham explains. "It's a problem of geography. Growers in other parts of the state have people lining up at the gate to take this stuff away."

Spent mushroom substrate contains high amounts of salts and other nutrients that must be leached out before the material can be used. Most producers spread excess SMS on unused farm fields to a depth of three to five feet. Left untouched for one to two years, the material is leached by rainfall. During this storage period, however, odors and nutrient runoff pose problems. Agronomist Richard Fox and soil chemist Jon Chorover are part of a Penn State project examining changes in SMS during the weathering process. They are working with Vincent Santucci, president of the Avondale, Pennsylvania-based Elite Mushrooms, to measure levels of nitrates and other nutrients that are leached from a small SMS storage field on Santucci's farm. The scientists installed lysimeters -- measurement devices that collect liquid leaching from the pile -- at the soil surface directly below the level of the compost, and three feet below that. "Even after being filtered through three feet of soil, the liquid leaching from SMS is dark brown, resembling strong tea," Fox says.

Workers at Elite Mushrooms, based in Avondale, Pennsylvania, pack and slice mushrooms headed for supermarkets. The business was established in 1908.

Fox's analysis of the liquid revealed that a 3-foot pile of SMS leaches 2,500 pounds of nitrates per acre into the soil -- 25 times the average nitrate level of 100 pounds per acre for a fertilized cornfield. A 5-foot pile releases 60 times the nitrates found in a fertilized cornfield's soil. Chorover, who focused on other compounds, such as calcium, magnesium, sodium, potassium, and organic carbon, reports the substrate also leaches high rates of organic carbon into the soil. "Organic carbon is what gives water a brown color," he explains. "A brown-water swamp will have carbon concentrations of 100 to 200 milligrams per liter. The water coming from the compost piles had carbon concentrations between 5,000 and 10,000 milligrams per liter."

Fox notes that the high concentrations of nitrates and carbon are concentrated in small areas. "The runoff from SMS piles had never been extensively analyzed before and the mushroom industry reacted positively, asking us to help find ways to reduce nutrient runoff," he explains. Before recommending solutions, Fox and Chorover must investigate how nitrate and carbon runoff affects groundwater in the area. Over the next 18 months, the scientists will monitor several 25-foot wells -- the level at which groundwater starts in Chester County.

College research projects also are finding new uses for SMS. While most research centers on using spent substrate in unique ways, Paul Wuest reexamined the mushroom production process. He and graduate student John Guardino are investigating whether used mushroom compost can replace the top layer of peat moss -- called "casing" in the industry -- that growers apply to retain moisture and provide a growing surface for mushrooms. "Most research 20 years ago, including some of my own projects, indicated that using SMS as a casing caused infestations of verticillium disease the most serious fungal disease of mushrooms, causing losses of about 6 percent each year," Wuest says. Today, the mushroom industry processes SMS differently after it leaves the mushroom house. Wuest and Guardino used SMS that had been leached before application and found that crop yields were equal to those using a peat moss casing. In addition, their trials revealed that using SMS as casing instead of peat moss actually reduced the incidence of verticillium disease. "We may have developed an effective nonchemical management tool for one of the worst diseases in the mushroom industry," Wuest says.

Floriculturist Jay Holcomb is evaluating the possibility of using spent mushroom substrate as a potting material for marigolds, poinsettias, and ornamental plants and shrubs. The research could benefit both mushroom growers and the green industry.

Floriculturist Jay Holcomb, an expert on greenhouse flower and plant production, hopes to find a fertile market for SMS as a potting material for greenhouse plants. Most commercial growers currently use peat moss, hardwood bark, or pine bark as a substitute for soil. "Growers want consistently reproducible crops," Holcomb explains. "Bark mixes and peat moss have no weed seeds, no disease problems, and the material is coming from a known source. With soil, you're never quite sure what you're getting." Its organic composition could make SMS an excellent growing medium, too. "I wondered whether or not the used SMS needed to spend a year in the field to have the salts and other materials leached out of it to be an acceptable product," Holcomb says.

Holcomb and horticulturist Charles Heuser found that leaching each pot of SMS three times with irrigation water -- a 15-minute process -- effectively removes excess salts. They have grown crops of marigolds, poinsettias, and 10 different species of ornamental plants and shrubs in the SMS and found it to be an effective growing medium. Heuser has asked several cooperating nurseries to grow a variety of SMS-potted plants under production conditions. There's just one potential hitch. "The material continues to decompose in the pot," Holcomb points out. "A full pot will be three-quarters full after nine months of growth. That's not a problem for proper growth, but it may be an appearance issue for customers."

Holcomb believes SMS can be a new source of potting medium for the green industry in Pennsylvania and nearby states. The counties with the most mushroom producers are very near the key counties in the green industry in southeastern Pennsylvania. Competing potting materials must be shipped in from greater distances: peat moss from Michigan and Canada, and wood bark from North and South Carolina and Georgia. "Mushroom companies have a problem disposing of SMS," he says. "At the same time, most greenhouse companies in Pennsylvania grow containerized plants, and they all have to use growing media. Used SMS can be a nice revenue stream for mushroom producers on a regional scale, because it is too bulky and heavy to make long-distance shipping profitable. Our goal is to expand the list of plants that will grow in it."