The University of Pretoria (UP) has developed an environment-friendly substrate, the Mabu casing, which is a suitable alternative to the peat soil used for button mushroom production.
Casing soil producer Mabu Casing Soils managing member Dr Linda Meyer says the substrate has the potential to protect the South African mushroom industry against currency fluctuations, increased environmental concerns and peatland depletion.
Mabu Casing Soils was established in 2011 to commercialise the Mabu substrate. The company is the sole intellectual property licensee and holds the rights to sublicence the technology globally.
Meyer reports that the technology has been successfully scaled up from the laboratory phase to the intermediate phase and is now in the commercial phase.
“The commercialisation process has been supported by energy and chemicals group Sasol’s enterprise development division Sasol Chemcity.
“We are currently at a production rate of 860 t/y and aim to produce 30 000 t/y [of casing soil],” Meyer states.
The search for a local alternative substrate to peat soil has been driven and funded by the South African Mushroom Farmers’ Association (Samfa) since 2002 and has been a focus of the mushroom research programme at UP, she adds.
Peat is a nonrenewable fossil fuel and South Africa currently imports peat soil for button mushroom production from the northern hemisphere, which is a nonsustainable solution.
She points out there has been considerable global environmental pressure against extracting this nonrenewable fossil fuel for use in the horticultural and mushroom industries.
Peat is an accumulation of partially decayed vegetation and forms when plant material, usually in wet areas, is inhibited by acidic and anaerobic conditions from decaying fully.
One of the most common northern-hemisphere peat components is sphagnum moss, but South Africa’s peatlands mainly comprise decomposed reeds, sedges and grasses.
The South African peatlands are less than 10 000 years old and form at a slow rate of 0.5 mm to 1 mm a year. Thousands of tons of peat have been mined outside Ventersdorp, Potchefstroom and Tarlton for the local mushroom industry.
In 2007, Samfa decided to stop the use of South African-mined peat to ensure that local resources are not depleted and is importing 50 000 t/y of peat soil at a high cost from the Neth- erlands, Canada and Ireland.
“While our remaining local resources are protected, global resources are still being depleted. Of all the natural ecosystems, peatlands are the most vulnerable to sustaining irreversible damage.
“Further, these wetlands are biodiversity hotspots and home to many endangered species. It is reported that these wetlands store at least 550 Gt of carbon – double that of the world’s forest biomass,” Meyer points out.
She adds that healthy peat absorbs and stores carbon, which is a major environmental benefit.
When peat is excavated, the organic carbon that has been stored and built up inside the material over thousands of years decomposes and is released into the atmosphere as carbon dioxide (CO2).
“About three-billion tons of CO2 a year are emitted through the unearthing and use of peat,” reports Meyer.
She states that the Mabu substrate will help the local mushroom industry preserve natural peatlands and endangered spe- cies, as well as maintain an environmental balance.
“The Mabu casing also offers potential for local production, which creates jobs and adds value to a waste product. It reduces transport and input costs for the mushroom farming industry.
The high carbon footprint of shipping and transporting the imported casing soil is a further incentive to seek a local alter- native casing substrate for button mushroom production,” says Meyer.
Mabu Casing Development
The mushroom industry abandoned its efforts in 2008 and halted the alternative casing project at UP, as alternatives could not measure up to the requirements for button mushroom production.
Between 2002 and 2008, the UP studied wattle bark, filter-cake, coir, braak seedling mix, oasis, boiler smuts, spent mushroom compost, perlite, vermiculite, clay, calcium bentonite, water hyacinth and sugarcane bagasse alternatives.
Nevertheless, the UP decided in 2009 to take raw substrates and change it according to the industry’s needs.
“Raw sugarcane bagasse pith is not suitable as a casing soil,” Meyer reports.
Instead, we developed a process to deplete the nutrients in the pith and improve the structure without losing its exceptional water holding capacity. This is how the Mabu casing came about,” she notes.
The process was patented by the UP in 2010 after an invention disclosure was filed with the university’s Department of Research and Innovation Support.
“We are increasing Mabu casing production as we advance in the commercial phase and realise that we still have a long way to go before we reach the 60 000 t required by the industry every year, which is what we hope to achieve in future,” Meyer concludes.