Unit 3: Mushroom bed Preparation

Mushroom Bed Substrates

The "mushroom bed" is the bulk material (substrate) that has been prepared and inoculated with spawn, from which the mushrooms will eventually fruit. The choice of substrate is critical and depends on the type of mushroom being grown.

This unit focuses on substrates for saprophytic mushrooms (like Oyster and Paddy Straw) which feed on dead plant matter.

Common Substrates:

• Paddy Straw: The most common substrate in India for growing Paddy Straw mushrooms (Volvariella) and Oyster mushrooms (Pleurotus). It is cheap, widely available after rice harvest, and has a good lignocellulose content.
• Sugarcane Trash (Bagasse): The fibrous residue left after sugarcane is crushed for juice. It is an excellent, readily available substrate in sugar-producing areas.
• Maize Straw (Corn Stalks): The leftover stalks, leaves, and cobs after harvesting maize. It needs to be chopped before use.
• Banana Leaves: Green or dried banana leaves can also be used, often mixed with other substrates.

General Preparation of Substrates (for Oyster Mushrooms)

1. Chopping: The substrate (e.g., paddy straw) is chopped into small pieces (1-2 inches) to allow for tighter packing and easier colonization by the mycelium.
2. Soaking: The straw is soaked in water for 8-12 hours to hydrate it fully.
3. Pasteurization: This is the most important step. The soaked straw is pasteurized (not sterilized) to kill competitor molds and bacteria, but not all beneficial microbes.
   • Hot Water Treatment: The straw is soaked in hot water (60-80°C) for 1-2 hours. This is a common low-cost method.
   • Steam Pasteurization: Done in a dedicated steam room, more common in commercial farms.
4. Draining and Cooling: The straw is removed, drained on a sieve, and allowed to cool to room temperature. It should be moist (60-70% humidity) but not dripping water when squeezed.
5. Inoculation ("Spawning"): The prepared spawn (from Unit 2) is mixed thoroughly with the cooled substrate.
6. Bagging: The mixture is tightly packed into polythene bags. Holes are often punched in the bag for air exchange.

Factors Affecting the Mushroom Bed Preparation

The success of the mushroom bed (now called a "grow bag" or "block") depends on several factors:

• Substrate Quality: The substrate must be clean, free from mold, and not overly decomposed.
• Moisture Content: This is critical. If too dry, the mycelium won't grow. If too wet, it will promote bacterial growth and block air (anaerobic), killing the mycelium. The ideal is 60-70%.
• Pasteurization: If not done correctly (too hot or too short), contaminants will survive. If "sterilized" (like in an autoclave), it can kill beneficial microbes and make the straw *more* prone to contamination.
• Spawn Rate: The amount of spawn used. A higher spawn rate (e.g., 5-10% by weight) leads to faster colonization, which gives contaminants less time to grow.
• Packing: The bag must be packed tightly to ensure good contact between the mycelium and the substrate, but not so tight that it blocks all air.

Low-cost Technology

This refers to methods of mushroom cultivation that are accessible to small-scale or rural farmers without expensive equipment.

• Using Thatched Huts: Building the growing house from locally sourced bamboo and thatch instead of a climate-controlled building.
• Hot Water Pasteurization: Using a simple drum and a fire (low-cost stove) to boil water for pasteurization, instead of a steam boiler.
• Local Substrates: Using whatever agricultural waste is free or cheap in the area (e.g., straw, sugarcane trash, banana leaves).
• Natural Humidity: Using a water sprayer and the thatched hut's natural properties to maintain humidity instead of electric foggers.

Composting Technology in Mushroom Production

This is a highly specialized technology used almost exclusively for the cultivation of the Button Mushroom (Agaricus bisporus).

Principle

Agaricus is a "secondary saprophyte." It cannot digest raw straw (cellulose and lignin). It needs a selective substrate (compost) where other microbes (bacteria, thermophilic fungi) have already broken down the raw materials and converted them into a rich food source. The composting process kills off most competitors, leaving a substrate that *only* the Agaricus mycelium can thrive on.

Phases of Composting:

1. Phase I: Outdoor Composting (Stacking)
   • Ingredients: A nitrogen-rich component (e.g., chicken manure) is mixed with a carbon-rich component (e.g., wheat straw) and gypsum (calcium sulfate).
   • Process: The materials are mixed, watered, and stacked in long piles. The microbes inside start to decompose the material, generating immense heat (70-80°C). The pile is turned (aerated) several times over 1-2 weeks.
   • Result: The straw softens, turns dark brown, and has a strong smell of ammonia.
2. Phase II: Pasteurization & Conditioning (Indoor)
   • Process: The Phase I compost is moved into a pasteurization room.
   • Pasteurization: The compost is steam-heated to 60°C to kill any remaining pests and competitor molds.
   • Conditioning: The temperature is then lowered to 45-50°C for several days. This allows beneficial thermophilic ("heat-loving") microbes to finish the compost and, crucially, remove all the ammonia, which is toxic to mushroom mycelium.

The final, dark, sweet-smelling, ammonia-free compost is then cooled and inoculated (spawned) with Agaricus spawn.