The Role of Casing Soil in Agaricus bisporus Cultivation

Agaricus bisporus, commonly known as the cultivated mushroom or white button mushroom, holds a special place in European cuisine. Its delicate flavor and versatility make it a staple ingredient in dishes ranging from creamy risottos to hearty stews. But what role does casing soil play in the successful cultivation of this beloved fungus? Let’s dig into the fascinating world of mushroom farming.

Understanding Casing Soil

Casing soil is a critical component in the cultivation of Agaricus bisporus. After the compost substrate is fully colonized by mycelium (the vegetative part of the fungus), it hardly produces mushrooms. The transition from vegetative mycelium to reproductive mycelium—the stage where mushrooms form—requires the application of a casing layer. Casing soil typically consists of a blend of materials, including:

• Peat: Traditionally, peat (either black or blonde) has been the primary component. It provides moisture retention and creates a favorable environment for mushroom development.
• Calcium Carbonate: Added to correct the pH of the casing soil (usually around 7–8).

The Crucial Role of Casing Soil

Creating the right environment

Casing soil maintains the necessary moisture levels. Mushrooms thrive in a humid environment, and the casing layer prevents excessive drying during the fruiting stage. It also hosts a diverse microbial community. These microorganisms contribute as an essential nitrogen source for Agaricus bisporus mycelium. By breaking down wheat straw in the composted substrate, they release sugar residues that nourish the growing mushrooms.

Microbiome dynamics

Researchers employ next-generation sequencing to study the microbial structure of casing soil during mushroom cultivation. They analyze both bacterial and fungal communities. As the incubation of Agaricus bisporus progresses, the microbial composition in the casing soil changes significantly. Key observations include Bacterial Dominance (Proteobacteria and Bacteroidota emerge as dominant bacterial phyla¹), as well as fungal shifts (Agaricus bisporus gradually displaces other fungal species, becoming the primary player). Some growers use fungicides to manage pathogens. However, some of these treatments can impact casing colonization by Agaricus bisporus.

Challenges and Sustainability

The mushroom industry faces a challenge in substituting peat-based casing materials. Within Bioschamp Project, sustainable alternatives are being explored. A deeper understanding of casing soil microbiomes could enhance biological efficiency during mushroom production.

A complex interplay from within the casing soil provides the optimal growing environment for mushroom production. Substrate producers, such as Kekkilä-BVB, work hard every day to maintain the consistent quality in the casing soil they manufacture.