July 18, 2011 | General

Recycling Mushroom Substrate

BioCycle July 2011, Vol. 52, No. 7, p. 25
A growers’ consortium established a successful soil amendment production, distribution and marketing arm to recycle large volumes of spent growing media.
Dan Sullivan and Randy Happel

LAUREL Valley Farms represents a consortium of seven large, commercial mushroom growers who joined forces in 1979 near Avondale in southeastern Pennsylvania – a region widely regarded as the mushroom growing capital of the world – to produce growing media for their industry. The media is made from wheat straw, hay, bedding from horse tracks and stables, corncobs and cotton-seed hulls, with poultry manure and cocoa bean shells added for nitrogen and gypsum to increase the alkalinity.
“It’s all blended together to make compost for growing mushrooms,” says Joe DiNorscia, manager at Laurel Valley Soils, Inc., which recycles the mushroom soil at the back end into valuable agriculture, gardening and landscaping products. “What it looks like to a layman is not what you would think of as compost. It looks like just a bunch of straw and hay that has a dark, caramelized color. What we are looking for is the dewaxing of the straw and hay through [partial] composting so the mycelium can attack it. It’s not totally composted.”
Since there are different substrate recipes for different families of mushrooms, compost feedstocks and proportions of each substrate ingredient will vary. “Agaricus bisporus – like your common white mushrooms and the portabella – shitakes, oyster mushrooms, lion’s mane and enokis all have their own substrates that they grow on,” DiNorscia adds. “Each has just a totally different preparation and ingredient base.”
One of the more difficult materials to handle is the poultry manure that offers the main source of each formula’s nitrogen content, explains Glen Cote, general manager of Laurel Valley Farms. The challenge is due to inconsistencies in moisture, texture, nitrogen and ash content (the farm takes in around 500 tons of poultry litter a week from all over the East Coast). After years of searching, Cotes and DiNorscia discovered the solution in a Vermeer HG6000 horizontal grinder. “What we were looking for was a way to grind poultry litter to achieve a consistency similar to that of soybean meal,” Cote explains. “We finally found it … After some initial trials and experimenting with different sized screens, it is really making a very beautiful product.” Once the poultry litter passes through a 3/4-inch screen, it is mixed with the other feedstocks in proportions dictated by the type of mushroom being grown.
Before the media is removed from the growing room, it is steam pasteurized to kill off any insects or competitor fungi (steam pasteurization also occurs five to seven days before the mushroom spawn is mixed in). The soil-like material remaining after the mushrooms are all harvested is rich in organic matter. “Once it comes out of the growing rooms it has a long way to go,” explains DiNorscia. “It’s what we call green compost for horticultural use.”
Within the past decade, the challenge of managing the substrate left over after the fungi were grown and removed – approximately 75 percent of the media by volume remains after harvest – began to grow out of control. “It was always a problem; we saw that it would get worse, not better,” says DiNorscia. “From a marketing standpoint we faced the same problems all other businesses did that were selling compost, being that very few people really understood the long-term benefits. That’s when the idea of starting a soils division to recycle the spent substrate and produce value-added soil amendments took root.” Founded in 2001, Laurel Valley Soils now serves as the soil amendment production, distribution and marketing arm of the parent company, Laurel Valley Farms.
All of the spent mushroom substrate utilized by Laurel Valley Farms is recycled by Laurel Valley Soils. “What we produce we take back,” explains DiNorscia. “None of it is used for growing mushrooms again – we process it all for the soils division.” Once the media has been synthesized by the mycelium, it cannot be reused. “Mushrooms take the carbon out in the form of cellulose and lignin – that is basically what they’re consuming,” he adds. “It still has a lot of carbon left in it, but the part that the mushrooms are consuming is gone.”
DiNorscia says his company tries to avoid the common but somewhat pejorative industry term “spent mushroom soil,” as it implies a product that is somewhat used up and that is not the case. “We just call it mushroom compost at that point,” he notes. “The NPK in the material when we created it is basically the same when the mushrooms are finished with it.”

The composting facility has expanded incrementally over the past decade. It is situated on a 128-acre parcel of land. The compost pad now encompasses 10 acres and houses two buildings dedicated to drying finished material for sale to landscapers, nurseries and resale-supply companies. “We produce more than 250,000 yards of compost annually,” says Cote. “This facet of our operation has become a primary source of income for the corporation.”
After the substrate has served its purpose at Laurel Valley Farms and is delivered to Laurel Valley Soils, the material is laid out in long windrows on the compost pad (constructed at a 2 percent slope). There are 18 to 20 windrows – 1,200-feet long and containing approximately 3,500 cubic yards of material each – on the pad at any given time. Excess moisture drains into a 5-million-gallon lagoon for approximately one week. Material remains on the pad and becomes stable over the next 13 to 14 weeks. Because it arrives so wet, maintaining moisture is never a problem, adds DiNorscia. “When we receive material, it is 65 to 70 percent moisture. We never have to add moisture.”
Windrows are turned once or twice a week with a Scarab turner. “The nature of the material, that being hyperactive biologically, makes it almost impossible to stop the core of the windrows from becoming anaerobic,” explains DiNorscia. “This usually happens as soon as 24 hours after we turn with the Scarab. The only way to stop this would be to install an aerated pad system, which is cost-prohibitive for our operation on a 10-acre site.”
When the windrows are initially turned, hardwood sawdust is added as a carbon source and bulking agent. The sawdust – added at a ratio of about 1:5 – comes from maple and oak logs that one of the mushroom houses grinds up to use as media for growing shitake mushrooms. “We test the compost regularly and strive to make sure that we keep things uniform from batch to batch,” says Cote. “We have been able to do this consistently because of the quality of raw materials we use from the beginning.”
Liquid collected in the massive lagoon from the maturing compost and also following a rain event is dispensed in two ways, says DiNorscia. “A primary pipeline goes back to the facility where they actually make the compost for growing mushrooms. They installed three irrigation ponds three years ago, and use the water from the composting process to make the mushroom compost.” The nutrient-laden water acts as stimulant to begin the composting process on the raw straw and hay. Leachate from the compost pad is also used to irrigate a 10-acre field of hay grown as feedstock for the mushroom growing media.
Laurel Valley Soils’ product line includes fresh (green) and aged mushroom soil, premium compost, enriched topsoil, a specialty product called TurfDress, custom blends and container media. Additionally, Laurel Valley has entered into a partnership with Skyland USA LLC to produce green roof growing media under the brand name “rooflite.” Blended in three different forms to offer the right balance of nutrients, water holding capacity and drainage for particular applications, rooflite meets both American Society of Testing Materials (ASTM) and German FFL Green Roof standards.
All products pass through one of three McCloskey trommel screens. “We typically screen to 1/2-inch minus,” says DiNorscia. “We also have a 3/8-inch minus screen that we can use on one of the machines for applications on top of a sports field or some other situation where a finer material is desired.”

Randy Happel is with Two Rivers Marketing in Des Moines, Iowa.

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