Detailed Explanation of Key Techniques for High-Yield Open-Field Mushroom Cultivation

Many factors affect the yield and quality of open-field mushroom cultivation. From years of production practice, we have found that in the path to achieving high-yield and high-quality open-field mushroom cultivation, spawn selection, compost heap building, bed preparation and spawning, field management, and integrated pest and disease control are five key links. We hereby summarize our research on the key techniques of these five links as follows, in the hope of being of some benefit to cultivators.

I. Spawn Selection

Strains obtained through tissue isolation or other means must undergo fruiting tests before they can be used on a large scale. The appearance of the spawn must have thick, white, uniform mycelium, with no interruptions in growth, no contamination by foreign microorganisms, and no pest damage (mainly mite damage). In terms of spawn age, solid-age spawn with mycelium fully covering the bottle (bag) within 1 month should be selected. Aged spawn shows yellow exudate and aerial mycelium clumps; when used in production, it shows poor revival ability, slow colonization, weak mycelium, low mushroom yield, and many tall-stiped mushrooms and mushrooms that open their caps easily. Therefore, in production, spawn selection should be treated with caution.

II. Compost Heap Building

Compost heap building is the most critical link among all the links. It involves two aspects: first, the quality of raw materials and a reasonable formula; second, the use of fermentation technology to allow the compost to be fully decomposed by actinomycetes.

1. Quality of raw materials and reasonable formula

The raw materials used for cultivating mushrooms must be fresh, dry, and free from mold. In the compost formula, the carbon-to-nitrogen ratio required for mushroom growth (generally 28-32:1) should be followed. The carbon-to-nitrogen ratio should neither be too low (excess nitrogen makes the compost prone to contamination or excessive ammonia inhibits mycelial growth), nor too high (insufficient nitrogen makes the compost lack nutrients). The carbon-to-nitrogen ratio of the compost can be roughly calculated based on the total carbon content and total nitrogen content of all raw materials. The compost formula should be flexibly controlled according to local raw material conditions and the requirement for a reasonable carbon-to-nitrogen ratio. The amount of cultivation material used is preferably 30-35 kg per sq m.

2. Compost heap building

The principle of compost heap building is, on the premise of a correct formula, to create conditions as much as possible to keep the compost in an aerobic fermentation state, so as to achieve the goal of building high-quality compost.

(1) Building the heap

The site for compost heap building should be chosen in a place with high terrain and good drainage. Before building the heap, prepare about 300 bricks of 12 cm x 24 cm and 1-2 pointed wooden sticks about 3-4 cm.

Taking manure-straw compost as an example, before building the heap, pre-wet the wheat straw with 1%-2% lime water for two days, and after it has fully absorbed water, mix and heap it with rice straw and other compost materials. In addition, poultry and livestock manure should be sun-dried, then fully soaked with water and broken up for later use. When building the heap, spread lime powder on the ground of the material yard, and build two rows of ground-hole bricks on the ground (two bricks 12 cm apart, placed upright along the direction of the heap, with two bricks laid horizontally on top as a cover), with 45-50 cm between the two rows of hole bricks to facilitate ventilation. First spread a 40 cm thick layer of grass material 1.5-1.8 cm wide, with no limit on length, add water, and scatter rice bran, oil cake, gypsum, wet manure, etc. Build the second layer, third layer, and up to the fifth layer in the same way. The last layer should consist only of grass material and be shaped like a turtle back. Make the four sides of the heap into neat vertical cut surfaces from top to bottom. This can, on the one hand, make the heap ferment evenly from top to bottom, and on the other hand, prevent rainwater from leaching into the lower part of the heap, causing uneven moisture and the proliferation of foreign microorganisms. After a section of the heap is completed, use pointed wooden sticks to make ventilation holes, with a hole spacing of 30-40 cm. After the entire heap is completed, insert a thermometer and prepare plastic film for heat preservation and rain protection. Note that before covering with plastic film, some branches should be placed on top of the heap; after covering with film, keep a gap of about 5 cm between the material and the film, and let the edge of the film hang down 30-40 cm. This can keep the top of the heap in a fully ventilated state.

According to our latest experiments: when building the heap, control a portion, and after the heap is completed and ventilation holes are inserted, add boiling water above 80°C along the holes; if conditions permit, steam can be introduced directly, which can rapidly raise the material temperature. After 48 hours, the material temperature can rise to about 62°C. The reason is that boiling water or steam raises the initial temperature of the heap and greatly activates the reproduction of actinomycetes. This method can not only shorten the heap-building time by about 3 days, but also significantly improve heap quality, with a yield increase of more than 10%.

The heap-building method for synthetic compost is basically the same as that for manure-straw compost. The superphosphate in both types of compost must be added at the second turning. Otherwise, superphosphate will react with lime to form solid high-calcium substances that mushroom mycelium finds difficult to absorb, greatly reducing fertilizer efficiency.

(2) Turning the heap

The only criterion for deciding whether to turn the heap is time. When the thermometer shows that the material temperature has reached 62°C, turn the heap for the first time. Likewise, build two rows of ground-hole bricks on the ground. First rake down about 20 cm of material from the outer surface of the heap, then shake the heap material loose and mix it evenly, turn it onto the ground into a heap 40-50 cm thick, and evenly turn the raked-off edge material onto the middle upper part. After that, mix and loosen the remaining material, turn the heap, and insert ventilation holes. Turn the heap 3-4 times in this way, and add superphosphate at the second turning. When the material is evenly covered with white actinomycete mycelium and the material appears coffee-colored, the heap is qualified.

Generally speaking, manure-straw compost requires 22-25 days of heap building, and synthetic compost requires 15-18 days. During the heap-building process, the material temperature should be checked at least twice a day. Rainwater must absolutely not be allowed to enter the heap. After each turning, support the top of the heap with branches, cover with plastic film, and keep a distance of about 5 cm between the top of the material and the film. At the same time, during the turning process, check the moisture content of the material by squeezing it by hand. If water drips out, the material is too wet and needs to be dried before rebuilding the heap. If there is only a water mark, the moisture is suitable. Since mushroom compost will also absorb soil moisture after being put into the field, the compost should preferably be dry rather than wet; the maximum moisture level is when the material is tightly squeezed by hand and a water mark appears between the fingers.

III. Bed Preparation and Spawning

In bed preparation, we changed the traditional flat bed surface to a one-bed two-trench method, increasing the yield per mu by about 5%. This method first makes beds 1.2 m wide and 16.5 cm high, with a trench width of 50 cm between beds. Then, on the bed surface, make two parallel material troughs of equal width, with a flat bottom and a depth of 16.5 cm, so that the entire bed surface is "w"-shaped. The soil ridge between the two material troughs is 10 cm wide. Finally, at the bottom of the material troughs, spread 3-5 cm of fresh dry rice straw that has been disinfected and treated for pest control. Note that in the process of bed preparation, one principle must be grasped: the bottom of the bed trench must be slightly lower than the bottom of the material trough, and drainage must be smooth. The reason the one-bed two-trench method increases mushroom yield is that it increases the contact surface between the compost mycelium and the soil.

One to two days before dismantling the heap, treat the heap surface with disinfectants and insecticides. After dismantling the heap, spread the compost in the material troughs to a thickness of 16.5 cm. When the material temperature drops to about 25°C, evenly scatter spawn on the material surface or sow in holes every 10 cm (the amount of spawn used this time accounts for 2/3 of the total spawn amount). Then spread a 3.3 cm thick layer of compost and sow the remaining spawn on the bed surface. Finally, spread 3-5 cm of fresh dry rice straw that has been disinfected and treated for pest control, use it to absorb dripping water from the plastic film, and cover with plastic film to preserve heat and moisture for mycelial growth.

IV. Field Management

Field management of mushrooms is the process of regulating temperature and humidity to promote mycelial decomposition of the compost, accumulation of nutrients, and fruiting. After spawning, when the temperature is high, the film should be uncovered for ventilation, on the one hand to promote mycelial growth, and on the other hand to remove excess moisture in the small space. When the mycelium has covered the material surface, remove the rice straw between the beds and cover with soil immediately. Loosen and break up the soil in the bed trenches (within 3 cm in diameter), adjust the moisture, scatter lime, mix evenly, and then spread it onto the bed surface. Then set up an arch frame on the bed, cover it with a thick grass curtain, and place the plastic film over the grass curtain, with the film edge hanging down to 2/3 of the grass curtain. In this way, it prevents rain, preserves heat and moisture, and the entire bed surface has good ventilation, which is conducive to mycelial growth and fruiting. During this process, attention should be paid to replenishing water on the soil surface.

When a small amount of mycelium extends out of the soil surface, the plastic film should be removed for fruiting management. During the fruiting process, attention should be paid to wet fruiting and dry mycelial growth. When spraying fruiting water, it is forbidden to spray mushrooms with cold water. Watering should be done on cloudy days or in the morning and evening of sunny days, using water close to the soil temperature to maintain moisture. After each flush of mushrooms is harvested, heat should be preserved for mycelial growth. After picking 2-3 flushes of mushrooms, apply 0.2% urea and 1%-2% potassium dihydrogen phosphate to the soil as a top dressing, which can increase the stamina for fruiting and raise yield.

V. Integrated Pest and Disease Control

Pest and disease control is an important part of mushroom production and must be integrated into every link of production to achieve the goal. If there is a problem in any one link, the entire production may fail. For example, if spawn contaminated or carrying pests, especially mite damage, is used, the entire compost will be ruined. Therefore, contaminated spawn or spawn with pest damage must be resolutely discarded. Spawn storage sites should be in a clean, pest-free environment. For growing mushrooms, on the one hand, paddy-upland rotation fields should be used as much as possible; on the other hand, insecticidal and fungicidal agents should be applied before use. One to two days before building the compost heap, place aluminum phosphide on the heap surface and cover tightly with plastic film to kill insects for 24 hours. The rice straw used for the bottom layer and covering the bed surface should be fumigated with formaldehyde and aluminum phosphide under film to kill insects and sterilize, and used after sun-drying. If pest damage occurs during mycelial growth or fruiting, place one aluminum phosphide tablet per sq m and cover with film to kill insects.