New intensive cultivation technology for small oyster mushrooms originated in South Korea

The small oyster mushroom belongs to the subdivision Basidiomycotina, order Agaricales, family Pleurotaceae, genus Pleurotus. It is rich in protein, sugars, vitamins, iron, calcium and the 8 essential amino acids for the human body. Its flesh is plump and tender, with a fresh and pleasant taste, and it has high edible and health-care value, making it highly favored by consumers. It is a mushroom with relatively large production and consumption in South Korea.

Because small oyster mushrooms are not easy to transport over long distances or keep fresh, very few fresh mushrooms are imported from abroad, and production is mainly domestic in South Korea. Compared with conventional oyster mushroom cultivation, the biological conversion rate of small oyster mushrooms is relatively low, only 50%-80%, and moreover, grading and packaging are relatively labor-intensive, so cultivation in South Korea, where labor costs are high, has no advantage to speak of. Therefore, many small oyster mushroom farms in South Korea are struggling to operate and are on the verge of bankruptcy. Seeking a breakthrough and regaining a new lease on life is a major issue facing small oyster mushroom producers.

The Xinyi Edible Fungi Research Institute of Pan'an County, Zhejiang Province, which takes technological innovation as its goal and business philosophy, conducted in-depth research on small oyster mushroom cultivation in South Korea. It also dispatched technicians to South Korea to carry out cultivation and experiments. Based on the demand characteristics of small oyster mushrooms in the South Korean market, the scientific and technical personnel of our institute focused on research into fruiting flushes and yield per flush, especially targeting the number of primordia formed, the rate of mushroom formation and uniformity, and made improvements in raw material formulation, environmental conditions and management measures. After many experiments, a set of low-consumption, high-efficiency intensive production technology suited to South Korea's national conditions was summarized.

This technology not only draws on the rapid effectiveness (high utilization rate) of factory production; it also absorbs the low-consumption nature (low cost) of traditional cultivation technology. By making up for each other's shortcomings and integrating advantages. After promotion and application at many cultivation farms, relatively good economic and comprehensive benefits have been obtained.

1 Mushroom house construction

There are large numbers of plastic greenhouses in the suburbs and rural areas of South Korea, and with slight modifications they can be used for small oyster mushroom cultivation. The modified greenhouse is 20 m long, 6-7 m wide and 2.2-2.5 m high. The greenhouse is mainly of steel frame structure. Two layers of agricultural film cover the greenhouse, with a layer of light-colored insulation cotton sandwiched between the films, and the outermost layer is covered with a layer of felt.

Advantages of this greenhouse: the small space is conducive to ventilation and air exchange and to operation and management. The environmental conditions inside the greenhouse are easy to control. The movable outer felt covering can be adjusted at will according to climate changes. It plays various roles at different cultivation stages (shading, cooling, insulation, etc.). On sunny days, open the felt to let in light and raise the temperature, making full use of natural resources; on cloudy and rainy days, cover it for insulation. When the temperature is too low, turn on heating devices to raise the temperature. Heating methods include piped heating, electricity, coal stoves, etc. Considering cost and practicality, coal stoves or sawdust stoves are generally used for heating. Place two stoves inside the greenhouse, connect iron sheet chimneys, and guide the smoke outside the greenhouse. This device is low in cost, fast in heating and convenient to operate, requiring only 2 fuel changes per day and no dedicated personnel to watch over it. An underground flue can also be built beneath the walkway (along the direction of the greenhouse), with the firing opening set at the end of the greenhouse or in the buffer room. Humidification uses atomizing micro-sprinklers or humidifiers to improve work efficiency, installed along the direction of the greenhouse so that humidity inside the greenhouse is distributed evenly.

2 Cultivation technology

2.1 Material preparation Intensive production is mainly reflected in saving time, saving energy, low consumption and high efficiency. The choice of raw materials is also crucial. For example, using cottonseed hulls as the main material and adding a small amount of auxiliary materials can make the flushes of small oyster mushrooms obvious and concentrated. This avoids the slow fruiting, unclear flushes, prolonged fruiting cycle, inconvenient management and rising costs of conventional cultivation technology.

2.2 Composting and fermentation The fermentation method for cultivating small oyster mushrooms is currently a relatively ideal approach. It avoids the high contamination rate of the raw material method and the high cost of the sterilized material method. It highlights advantages such as fewer contaminating microorganisms, fast mycelial growth and fast fruiting.

After the raw materials are mixed and fully stirred evenly, pile them into a trapezoidal compost pile with a bottom width of 2 m, a top width of 1.5 m and a height of 1.2-1.5 m. The fermentation time is 9-12 d, during which the pile is turned 3 times. When the temperature is low, it is best to carry out this indoors or inside the greenhouse, so as not to prolong the composting time and affect the fermentation effect.

2.3 Bagging Spread out the well-fermented raw materials to let gases such as ammonia that hinder mycelial growth volatilize, and begin bagging after the material temperature drops to 30 °C.

The bagging method is: three layers of spawn and two layers of material. That is, spread one layer at each end, with one layer of spawn sandwiched in the middle. Bagging and inoculation are carried out simultaneously. After bagging, tie the bag opening tightly, then stack the bags in a wall-style pile. The pile height should preferably be 7 layers. Leave a walkway of 70 cm between piles; too narrow is unfavorable for operation and affects work efficiency. The bags should be placed close together, leaving as few gaps as possible. It is also inadvisable to lift and squeeze the material bags with force, causing the bag wall to separate, so as to avoid fruiting in the gaps and consuming nutrients. Finally, use a conical wooden stick 1.5 cm in diameter to poke two oxygen-enhancing holes through the material bag at one end of the bag to promote mycelial growth.

The single weight of the material bag and the specifications of the plastic bag have always been a focus of controversy in the industry. Some people believe that small bags hold less material and have lower yield, and although the cycle is shorter, they cost more labor; others believe that large bags hold more material and have higher yield, but the cycle is longer and the benefit is not actually high. It can be said that everyone has their own views. We believe that large and small bags each have advantages and disadvantages. Adapting to local conditions and handling matters flexibly is the best policy. Through research and comparative cultivation experiments, the conclusion is drawn: the method of plastic bags with specifications of 18 cm x 45 cm (length after filling is 30 cm) and 0.6 kg of dry material per bag is more suitable for intensive production.

2.4 Mycelial growth management The quality of mycelial growth directly affects the time and effect of fruiting. In order to coordinate with intensive production and make fruiting fast and concentrated. Indoor constant temperature and dim light should be controlled as much as possible. Drastic temperature changes will affect the normal growth of mycelia and easily stimulate early fruiting, leading to non-concentrated flushes and unstable yield. If the light is too strong, it is easy for a mycelial film to form on the surface of the mycelium, consuming nutrients and affecting the quality and yield of the mushrooms. From after inoculation until the mycelia fully cover the bag, the room should be kept dark. But within 1 week after the mycelia fully cover the bag, the bags should be exposed to light (gradually increasing), so that the bags gradually adapt, which is also conducive to uniform pinning. During the culture period, control the temperature at 22-24 °C and the relative humidity at 70%.

2.5 Fruiting management What differs from conventional cultivation is that the intensive technology adopts the fixed-position fruiting method. The oyster mushrooms grow from the oxygen-enhancing holes reserved during bagging, which can effectively prevent large numbers of mushroom buds from shrinking due to competition for nutrients, causing unnecessary loss of nutrients. At the same time, conventional open-mouth fruiting produces mushroom clusters that are too large, with many dead mushrooms and poor mushroom shape, and processing and packaging cost labor. In the fixed-position fruiting method, the bag opening is not opened, so the bags lose less water through evaporation, having less impact on the growth of the second flush.

The South Korean market requires that small oyster mushrooms must be single, with long stipes and small caps. Mushrooms produced by the fixed-position method exactly meet the standard, and moreover, the mushroom formation rate is high, there are few small mushrooms attached to the stipes, and the degree of commercialization is high, making harvesting, processing and packaging convenient.

After the mushroom bags are treated with weak light, increase the light intensity, increase humidity and lower the temperature to promote concentrated formation of mushroom buds.

After stimulation by high humidity, light and low temperature, the reserved oxygen-enhancing holes are the first to come into contact with environmental conditions suitable for fruiting, while other parts are not prone to fruiting because the plastic bag clings tightly to the mycelium.

Fruiting management is divided into three stages: the primordium differentiation stage, the mushroom bud formation stage and the fruiting body growth stage. The technical key points are: "promote", "maintain" and "nurture".

2.5.1 Promotion In the early stage, promote the differentiation and formation of primordia. Create suitable environmental conditions. The specific method: lower the temperature to 8-12 °C, reduce ventilation, increase light intensity, raise the relative humidity of the space, and spray the space so that the fruiting openings (the original oxygen-enhancing holes) appear moist but without standing water. With such continuous treatment for 4 d, uniform pinning can be achieved. This makes the time of primordium formation easy to grasp accurately and controls uniformity.

2.5.2 Maintenance In the middle stage, ensure the survival of the mushroom buds. Stabilize environmental conditions, avoid shrinkage and death of mushroom buds, and increase the mushroom formation rate.

At this stage, the environmental conditions should be kept relatively stable, with relative humidity controlled at 85%-90% and temperature at 12-15 °C. Factors such as a large temperature-humidity difference and strong hot or cold winds will all affect the formation and growth of mushroom buds.

2.5.3 Nurturing In the later stage, cultivate high-quality mushrooms. Adjust environmental conditions so that the mushroom flesh is firm and dense and the mushroom shape is round and proper, increase unit yield, and ensure high quality and high yield.

When the mushroom buds form normally and grow to a cap diameter of 1.5 cm, their ability to adapt to the environment has increased. Slight fluctuations in temperature and humidity have little effect, and moderate changes can instead make the mushroom body plump and firm. At the same time, by regulating carbon dioxide concentration and light intensity, the shape and quality of the fruiting bodies are controlled so as to meet the special requirements of the South Korean market. At this stage, controlling the diameter of the mushroom cap is crucial. Because the edible part of conventional oyster mushrooms is the cap, for which a large cap and short stipe are preferable; small oyster mushrooms are exactly the opposite. Therefore, major adjustments should be made in management, increasing carbon dioxide concentration and reducing light intensity to control the growth of the mushroom cap and promote the growth of the stipe.

2.6 Harvesting When the stipe reaches 5-7 cm in length and the cap diameter is 2-3 cm, they can be harvested. Because intensive technology is adopted, the formation and growth of fruiting bodies are relatively concentrated and uniform, the harvest period is shorter, saving time and improving efficiency, and it is also conducive to flush transition management.

During harvesting, care should be taken and the mushrooms handled gently. The containers used should preferably be shallow baskets with a single layer arrangement, so as to avoid breakage caused by stacking and squeezing the mushroom bodies and affecting quality.

After the first flush is harvested, clean up the residual stipes and debris. Stop humidification and maintain constant temperature to restore the mycelia for 5-7 d. Then enter the management of the second flush according to the management method of the first flush. At the third flush, cut away the plastic bag at the opening and open the mouth for full-surface fruiting. The mushrooms produced at this time are slightly lower in quality, mainly to shorten the fruiting cycle. The first two flushes have better quality, and their yield also accounts for more than 70%-80% of the total yield. Generally, completing 3 flushes takes about 60 d (when environmental conditions are not available, the fruiting cycle will be prolonged). Each bag can produce about 500 g of mushrooms, with a conversion rate of about 80%.

2.7 Packaging Break clustered or joined mushrooms into individual ones, and use scissors or a knife to trim off debris attached to the stipes. Then grade them and put them into plastic bags, tie the bag openings tightly, with a net weight of 2 kg per bag. When using cardboard box packaging, grading and processing should be carried out according to customer requirements.