Canadian mushroom growers now have a profitable option when it comes to dealing with the leftover organic substrate used to grow mushrooms.
Ron Fleming of the University of Guelph's Ridgetown Campus has found that spent mushroom substrate - manure-based material - can be fully composted and give rise to a high-quality material that can be sold at a premium.

"Composting can give mushroom growers an alternative method of dealing with this substrate while providing an additional income source," Fleming says. 

On a world scale, about 13.6 million tonnes of substrate are produced each year, he says. Normally, it's disposed of, spread on farmland or sometimes sold to other farmers.

When applied to land, spent mushroom substrate improves soil structure by increasing the water - and nutrient - holding capacity and adding organic matter. It's more consistent than many other compost products because the mix recipe stays fairly constant year-round.

As a bonus, it's free from weeds and disease because it's already been partially composted and fully pasteurized before being removed from the mushroom house.

Because of the compost mix recipe needed for mushroom production, however, the finished compost has a higher salt content than other composts. This can put some limitations on how the compost can be used.

In the past, the industry has dealt with the high salt content by stacking spent mushroom substrate outside for at least six months, allowing precipitation to leach out the salt. But this approach creates concerns related to Ontario's Nutrient Management Act because of the potential to contaminate surface and groundwater.

So in 2005, the Canadian Mushroom Growers' Association asked Fleming to find other options to deal with the substrate.

He turned to his expertise in anaerobic digestion to see if spent mushroom substrate could be used to generate methane gas. But the substrate didn't generate enough energy to be viable. In fact, the methane produced wasn't even enough to heat and run the digester.


Instead he found that a complete composting process could be used to improve the soil application qualities of spent mushroom substrate. The substrate was mixed and aerated for four weeks to create premium compost. In Ontario, selling this material in bulk garners up to $60 per tonne.
Fleming notes that the initial capital costs of the compost system are significant and include site preparation, composting structures, aeration fans, tractors and storage. But if the compost fetches a good price, the process can be economically viable, he says.

"Composting is safer for the environment and results in finished compost that has an excellent feel and appearance. Branding this as superior to other composts will be the ultimate factor in whether farmers can reap benefits."
By KATE ROBERTS & MARTIN SCHWALBE,
Source: www.guelphmercury.com