Sustainable mushroom growing

Mushroom farming is going green by replacing peat casing with sugar cane pith substrate. Linda Meyer spoke to Lindi van Rooyen at Mabu Casing Soils about how pith is saving peatlands.

The major component of casing soil traditionally used by mushroom growers is peat soil from bog environments or wetlands
Photo: Courtesy of Mabu Casing

Of all the natural ecosystems, peatlands are the most vulnerable to irreversible damage of the landscape. It is reported that these wetlands store at least 550 gigatons of carbon – double that of the world’s forest biomass. But when peat is excavated, the organic carbon that has built up and has been stored there for thousands of years decomposes and turns into CO2.

In South Africa, thousands of tons of peat have been mined outside Ventersdorp, Potchefstroom and Tarlton for the local mushroom industry. But since the South African Mushroom Farmers’ Association decided in 2007 to stop the use of SA-mined peat, 50 000t of peat soil has been imported from the Netherlands, Canada and Ireland annually. The high carbon footprint due to transport of imported casing soil is a further incentive to seek an alternative casing substrate for button mushroom production.

Pith casing
After many years of research, the University of Pretoria has come up with a solution for mushroom farmers in the form of casing soil made from sugar cane pith substrate. Linda Meyer, a researcher at the University of Pretoria and managing member at Mabu Casing Soils, says that the exceptional water-holding capacity of pith cells in sugar cane bagasse makes it unsuitable for the paper process, but perfect for growing mushrooms.

Processed pith casing has a suitable pH, does not break down after repeated watering and has a coarse and open structure which is ideal for mushroom growing. Courtesy of Mabu Casing

“In addition to good water-holding capacity, processed pith casing is free from pests and disease, has a suitable pH level, does not break down after repeated watering, and has a coarse and open structure that supports strong stranding and generation pinning in mushroom growing,” says Meyer. “Pith is a waste product of the pulp manufacturing industry, which makes it a cost-effective and environmentally-friendly alternative to peat. Mabu Casing Soils aims, for the first time, to produce more than 200t of casing.

This local alternative protects the mushroom industry against currency fluctuations and also against the increased environmental and customer concerns and regulation of peat land exploitation. Meyer says that local production of an alternative casing material not only has a very positive carbon footprint, but creates jobs and reduces transport and input costs of the mushroom farming industry. Local farmers are currently assisting Mabu in developing specialised application, watering and growing protocols for quality mushrooms in pith casing.

Contact Linda Meyer at [email protected]