Detailed Explanation of Key Technical Points for Casing Soil in Mushroom Cultivation

In the process of mushroom cultivation management, casing soil is an important task carried out after spawning, and its technical requirements are very high. The casing soil technique for mushrooms is described below.

1. Selection and treatment of casing soil materials

(1) Material selection The casing soil material is required to have good water absorption and water retention capacity, and at the same time good aeration. It is best to choose a neutral clay loam with a clay content of about 40%, a granular structure, and a small amount of humus. This kind of soil is not sticky when wet, does not crumble when dry, and has cracks at the edges of the soil particles. Through comparative tests on paddy field soil, wheat field soil, and vegetable garden soil, it was found that vegetable garden soil, because of its high nitrogen content, easily causes excessive vegetative growth of mycelium, produces physiological diseases such as "mycelial film" and "mycelial mat", and yields fewer mushrooms per unit area; it also carries more pathogenic spores and insect eggs, and easily causes diseases and pests. Wheat field soil has good aeration, water retention, and water-holding capacity, yields more mushrooms per unit area, and has relatively fewer diseases and pests. Paddy field soil with good soil structure differs little from wheat field soil. For soil with strong clay content, adding 30%-50% yellow mud, or adding 5% fresh rice husks (there should be no rice grains in the husks) also gives good results. River mud and pond mud from areas where mushroom diseases and pests occur severely are prohibited.

(2) Material treatment

1) Soil collection: One month before casing, dig soil from land where mushroom spent compost has not been applied that year. When collecting soil, first remove the topsoil 4-6 cm, then dig the soil, and expose it to the sun until dry, then break it up, remove impurities, and sieve it. The sieve aperture diameter for coarse soil is 2 cm, and for fine soil 1.5 cm. The soil particles should not be too large, and the soil texture should not be too hard.

2) Treatment: Generally, about 3 tons of soil are needed for 100 sq m of cultivation area. This requires 30 kg of lime, 10-15 kg of formaldehyde, 0.5 kg of dichlorvos, and 50-125 kg of rice husk. First mix these four materials evenly (leave a small amount of formaldehyde and dichlorvos to spray in when adjusting the water content after mixing the soil), then repeatedly mix thoroughly with the cultivation soil, adjust the water content until it can be formed into a ball by hand and does not crumble when dropped, with a pH value of 7-7.5. Cover with film and seal for 24 hours, then uncover the film, and after the chemical odor has dissipated, apply the casing soil to the beds. After the casing soil is prepared, it must be protected from rain to ensure a good granular structure.

2. Casing time

Generally, 14-20 days after mushroom spawn is sown, when the mycelium spreading from each spawn hole has approached one another and has grown to a depth of more than two-thirds of the compost, casing is most suitable. If, in order to produce mushrooms earlier, casing is done before the mycelium has grown to the bottom, the result is that the mycelium on the surface of the compost grows upward into the soil layer, while the mycelium inside the compost continues to grow downward. Mycelium growing in two directions climbs into the soil more slowly, instead delaying the time of mushroom emergence, and the yield is instead lower.

3. Casing and management

(1) Preparatory work before casing

1) Eliminating diseases: When inspecting the compost, if latent contaminating microorganisms and pests are found, especially green mold and mites, they must be eliminated before casing; otherwise, under the protection of the soil layer, they will be difficult to completely eliminate.

2) Drying the surface of the compost: The surface of the compost should remain dry, so that after casing and water adjustment the mycelium quickly resumes growth and climbs into the soil rapidly. Never spray water on the surface of the compost. If the surface of the compost is relatively moist, open the doors and windows for strong ventilation to dry the surface of the compost.

3) "Scratching the mycelium": Before casing, gently scratch and level the surface of the compost by hand, then gently pat it level with a wooden board. In this way, the mycelium on the surface of the compost is damaged and broken into more mycelial fragments. After casing and water adjustment, the mycelial fragments resume growth one after another, and more and more vigorous fluffy mycelium grows on the surface of the compost and into the soil layer, which can increase yield by 15%-20%.

(2) Casing method and thickness

1) Method: Use double casing, first covering with coarse soil, then covering with fine soil. When casing, first evenly cover the surface of the compost with the large soil particles, then gently pat level with a wooden board. After adjusting the water content in the large soil particles, evenly sprinkle the small soil particles on top to cover them.

2) Thickness: The total thickness of the casing soil is generally 4 cm, of which coarse soil is 2.5-3 cm and fine soil is 1.5-1 cm. The thickness of the casing soil layer should be uniform. If the casing soil is too thick, because the fruiting bodies are positioned low, it often leads to long mushroom stipes, non-round mushroom shape, the appearance of "landmine mushrooms" or "mud-topped mushrooms", and it is easy to grow large fruiting bodies. If the casing soil is too thin, the mycelium easily knots and forms primordia in clusters, creating a certain survival competition, and small mushrooms, thin mushrooms, joined stipes, and dead mushrooms will appear. In production, the thickness of the casing soil layer can be used to regulate the size of the fruiting bodies and improve mushroom quality. In addition, the total thickness of the casing soil should also vary according to the humidity of the mushroom house. If the humidity of the mushroom house is relatively high and the compost is on the wet side, the casing soil can be slightly thinner; otherwise, the casing soil should be thicker.

(3) Treatment after casing

1) Sterilization and pest elimination: Within 3 days after casing, use the high-efficiency mushroom fungicide developed by the Fujian Provincial Mushroom Spawn Research and Extension Station, 400 g/230 sq m plus 160 kg of water, and evenly spray it on the casing soil layer and in the mushroom house and its surroundings to prevent contamination by foreign microorganisms.

2) Water adjustment: The principle for adjusting water in the coarse soil is to keep it wet first and dry later, prompting the mycelium to grow inside and below the moist coarse soil and not extend to the surface of the coarse soil; for the fine soil, the principle is to keep it dry first and wet later. In the early stage, the fine soil is drier than the coarse soil, prompting the mycelium to continue growing in the coarse soil layer and fully grow into the interior of the coarse soil. Later, gradually increase the amount of water sprayed, prompting the mycelium to grow between the coarse soil and the fine soil without extending out of the soil surface. Once the mycelium grows into the fine soil, promptly strengthen ventilation and lower the temperature, making the surface of the fine soil relatively dry, forcing the mycelium to grow horizontally in the relatively humid environment below the fine soil and above the coarse soil, and to knot into mushroom primordia.