Detailed Explanation of Key Techniques for Outdoor Substitute Substrate Cultivation of Shiitake Mushrooms

Shiitake mushroom (Lentinula edodes) is one of the important edible fungi, originally wild, and was first artificially cultivated in China over 800 years ago. Substitute substrate cultivation uses artificial mushroom logs made from sawdust, mulberry branch powder, cottonseed hulls, etc., to replace natural logs for cultivating shiitake mushrooms. This method has wide resource availability, high yield, a short production cycle and high economic returns, making it very suitable for farmers to cultivate.

1. Strain Selection

There are many types of shiitake varieties, and the commonly used ones are of the medium-low temperature type. The optimal environmental conditions for the mycelial growth of this type of shiitake are an air temperature of 24-27°C, a substrate moisture content of about 60%, and no light or weak light. The optimal environmental conditions during the fruiting stage are an air temperature of 8-16°C, fresh and humid air, and 30% sunlight to 70% shade. When actually selecting strains, medium-temperature types such as 856, CrO 2 and L26 can be chosen. Each bottle of spawn is required to be free of contaminating microorganisms and pests, with pure strain characteristics and robust mycelial growth.

2. Substrate Preparation

The substrate composition includes miscellaneous hardwood sawdust, bran or rice bran, sugar, gypsum powder, urea, superphosphate, etc. Miscellaneous hardwood sawdust is the main carbon source material for shiitake mycelium; broadleaf tree sawdust from sawmills can be used, as can crushed material from defective waste wood and branches of broadleaf trees. Bran or rice bran is the main nitrogen-supplying material for shiitake, and fresh material free of mold should be selected. Sugar is a quick-acting carbon source absorbed and utilized by the mycelium in the early stage of growth and development, and either white sugar or brown sugar can be used. Gypsum powder can both provide calcium and delay the acidification process of the substrate. Urea and superphosphate are nitrogen fertilizer and phosphorus fertilizer respectively, providing nutrients such as nitrogen, phosphorus and calcium. The substrate formulas are: miscellaneous hardwood sawdust 77%, bran or rice bran 20%, sugar 1.2%, gypsum 1.8%; or miscellaneous hardwood sawdust 78%, bran 16%, corn meal 2%, gypsum 2%, superphosphate 0.5%, urea 0.3%, sugar 1.2%. First dissolve the soluble urea, superphosphate, sugar, etc. in water; dry-mix the other powdered materials together, then mix them in while adding water, repeating several times. Add water to the degree that the mixture forms a ball when squeezed by hand and crumbles when touched; at this point the moisture content is about 60%.

3. Sterilization

Cut low-pressure polyethylene tubular film with a folded diameter of 15 cm and a thickness of 0.04 mm into 55 cm-long tube sections, and seal one end. Fill the substrate into the plastic tube bags, each bag weighing about 0.9 kg (dry material), tie the opening, and place into a normal-pressure sterilization stove. Leave a certain space in the center of the stove to promote even steam distribution and improve sterilization effectiveness. Heat with a strong fire; when the temperature in the stove rises to 100°C, switch to a gentle fire and continue for 10-12 hours, then stop heating, and remove the materials when the temperature drops to about 70°C.

4. Inoculation

Wait until the substrate tubes have cooled to below 28°C, then together with inoculation tools and supplies such as an alcohol lamp, inoculation box, hole punch and inoculation rake, first disinfect the surfaces with 0.25% benzalkonium bromide solution, then move them into the inoculation box. Add 10 ml of formalin and 5 g of potassium permanganate per cubic meter of space, mix them, close the glass window and operation holes, and fumigate for half an hour; this can coagulate and denature microbial cell proteins and kill them. Afterward, the inoculating personnel wash their hands with 75% alcohol, reach into the inoculation box, and inoculate while punching holes, at the same time applying adhesive tape. This process requires quick movements and a short duration. The adhesive tape can be special tape for edible fungi or medical adhesive tape, with a size of 3.5 cm x 3.5 cm.

5. Mycelial Growth Management

Move the inoculated tube materials into a clean, dry room and stack them in a "#" shape to a height of 80-90 cm. Frequently open windows for ventilation, and during this period turn the stacks 2-3 times and remove tube materials contaminated by undesirable microorganisms. After 40-50 days, the mycelium grows throughout the tube bags; at this point they are called "artificial mushroom logs." When most artificial mushroom logs show a small number of brown patches, they can be transferred to fruiting management.

6. Building the Mushroom Shed

Choose dry land or idle winter land near a water source, dig a bed 1 m wide and 15-20 cm deep, and on the bed surface build a mushroom rack 30 cm high like a horizontally placed ladder and a small arched shed 1 m high at the center; on this basis, build a shade shed, generally 1.8-2.5 m high, with straw curtains covering the surroundings and top so that 30% sunlight can penetrate.

7. Bag Removal

Strip the tube film from the mature artificial mushroom logs and lean them obliquely on the mushroom rack, with a spacing of about 10 cm between each bag. Immediately cover with plastic film (preferably 0.07 mm-thick agricultural high-pressure polyethylene film) to retain heat and moisture.

8. Fruiting Management

Within 3-4 days after bag removal, keep the air temperature inside the film at about 26°C and the relative air humidity above 85%. After the surface of the mushroom tubes is covered with white fluffy mycelium, ventilate 1-2 times a day for half an hour each time to force the fluffy mycelium to lie flat. After 1 week, tea-colored small water droplets will appear on the surface of the mushroom tubes, and the mycelial film will gradually thicken and darken in color. At this point, spray water to wash off the brown secretions, cover the film by day and uncover it at night, and increase the day-night temperature difference; after 3-4 days, small protrusions, namely mushroom buds, grow on the surface. Shiitake is a mushroom that fruits under variable temperatures, and the buds need low temperature and day-night temperature difference stimulation to form. Afterward, continue to retain heat and moisture, and strengthen film uncovering and ventilation, and the small buds will gradually grow larger. Harvest and dry when the caps are eight-tenths mature and show a copper-gong rim shape.

After each flush of mushrooms is harvested, strengthen ventilation, stop spraying water for 3-5 days to rest and restore the mycelium, and then return to fruiting management; after roughly 1 month, the second flush can be harvested. After harvesting 2-3 flushes, use an iron wire to poke a hole in the center of the artificial mushroom log, press a heavy object on the log, and soak it in water. When the weight of the artificial mushroom log is close to its original weight, take it out, keep it warm inside the film to grow mycelium for 2-3 days, strengthen film uncovering and ventilation, and promote the formation and growth of the next flush. Repeat this cycle until it ends in May or June of the following year.

Throughout the fruiting stage, in early autumn and late spring, prevent high temperatures from burning the mycelium and rotting the substrate; in winter, especially during the mushroom bud stage, pay attention to keeping warm and preventing freezing; in addition, do a good job of disease and pest control.