Study on the Application of Pollution-Free Compound Nutrient Solution in Edible Fungi

Study on the Application of Pollution-Free Compound Nutrient Solution in Edible Fungi

Edible fungi are heterotrophic organisms lacking chlorophyll. Their growth and development depend on mycelium and the biodegradation of organic matter by microorganisms to obtain nutrients, so the yield of edible fungi is closely related to the nutrient level of their cultivation substrate. In general edible fungi production, the base material is prepared all at once before spawning, and after spawning only water adjustment, ventilation and air humidity are managed. This kind of production management has two problems: first, after inoculation, because the available nutrients in the base material are relatively few, the mycelium cannot rapidly propagate and grow; second, in the middle and late stages of growth, especially during the third flush period, because there is no supplemental external nutrition, the growth requirements of the developing fruiting bodies cannot be well met, which affects the yield of edible fungi [Jishan Huayao]. Experiments have proved that during the peak fruiting period and the middle and late stages, when the nutrients in the substrate are nearly exhausted, timely nutrient supplementation during these two important periods can significantly increase yield and improve quality. At present, most mushroom growers often use nutrient solutions whose main components are chemical fertilizers, yield-increasing agents and hormones. Although these can significantly increase yield, they have problems such as unstable yield-increasing effects and certain residues. This paper studies a pollution-free, low-cost and nutrition-enhanced compound nutrient solution for edible fungi, providing a reference for mushroom growers in edible fungi production.

1 Materials and Methods

1.1 Experimental Materials

The test material was biogas slurry, taken from No. 1 and No. 2 biogas digesters producing gas normally in Lijiazui Village, Neiguan Town, Anding District. The main raw material of the biogas digesters was pig manure. During sampling, relevant regulations were strictly followed, and the samples were divided into plastic bottles washed with digestion solution, stored and sent for testing. The test items included total nitrogen, total phosphorus and total potassium, as well as mineral elements in the biogas slurry such as phosphorus, potassium, sodium and magnesium.

1.2 Determination of Element Content

Biogas slurry samples were determined at our unit. Total nitrogen was determined by the Kjeldahl method, total phosphorus by the acid solution-molybdenum-antimony anti-colorimetric method, and total potassium by flame photometry (Table 1). Mineral trace elements (phosphorus, sodium, potassium, magnesium, copper, iron, manganese, zinc, calcium and sulfur) were determined by wet ashing-atomic absorption spectrometry (Table 2).

Table 1 Variation range of main nutrient contents in biogas slurry /%

Table 2 Contents of main mineral elements in biogas slurry

Although the nutrient content of biogas slurry is not high, these nutrients are mainly quick-acting. Because the fermented material has been soaked in water for a long time, some soluble components can be transformed from the solid phase to the liquid phase, thereby greatly increasing the content of quick-acting nutrients (Table 1). Among the main mineral elements contained in biogas slurry (Table 2), the contents of phosphorus, potassium and magnesium, which are most important for the growth and development of edible fungi, are relatively high, with magnesium content being the highest. Therefore, as long as there is some biogas slurry or biogas residue, phosphorus dihydrogen potassium and other fertilizers are not needed for making spawn. Other trace elements such as iron, cobalt, manganese, zinc and molybdenum are needed in smaller amounts; these elements exist in ordinary water, so no additional nutrients are added. Biogas slurry and biogas residue fully possess the elements lacking in the spent mushroom substrate after mushroom production.

1.3 Preparation of Nutrient Solution

After fresh biogas slurry is pumped from the biogas digester with a pump hose, it is placed in a cool place, first filtered with a filter screen, and then a certain amount (a small amount) of chemical fertilizer aqueous solution is added to it, stirred repeatedly and set aside. When the temperature is relatively high, a certain amount of quicklime clarified liquid is added. If diseases and insect pests are found in the mushroom bags or mushroom beds, kemeling and some high-efficiency low-toxicity insecticides can be added.

2 Results and Analysis

2.1 Technology for Supplementing Nutrient Solution in Bag-Cultivated Edible Fungi

2.1.1 Time for supplementing nutrient solution First, observe the mycelial growth in the mushroom bag, that is, whether it is vigorous, and the whiteness and density of the mycelium. Second, check whether the water content of the culture material in the mushroom bag has fallen below 50%; in addition, the natural temperature should remain continuously above 9 °C. If the above conditions are met, the culture material can be continuously supplemented with compound nutrient solution 1 to 3 times during the fruiting period. The first supplementation can be done at the end of harvesting the first 2 flushes,

and the second supplementation can be done when the 4th flush has been completely harvested. If the following situations occur: the mycelium in the bag is thin and yellow, the water in the culture material is sufficient, diseases and insect pests have already appeared in the culture material, or the temperature drops below 4 °C, then it is not suitable to add supplemental compound nutrient solution.

2.1.2 Method of supplementing nutrient solution After the first 2 flushes of oyster mushrooms have been harvested, connect a special water replenisher, the switch and other parts on a sprayer, to 1 pipe, with the other end connected to a tap. First insert the water replenisher into the culture material, then open the spare switch on the water pipe to supplement water into the material. When the mass of the mushroom bag reaches the mass at the time of bagging or slightly higher, the nutrient solution supplementation is considered appropriate. Generally, for a mushroom log bag filled with 1 kg of dry material, the mass after water supplementation should reach 2.5 kg. After supplementing the nutrient solution, 2 to 3 flushes of high-quality oyster mushrooms can be produced continuously, and the total yield can be increased by 50% compared with the conventional fruiting method. If the nutrient solution was not supplemented in the early stage, as long as the mycelium in the material grows vigorously, the nutrient solution can still be supplemented after harvesting 3 to 4 flushes when the temperature is above 10 °C, but the amount of water supplemented should be greatly reduced. In high-temperature seasons, add kemeling and high-efficiency low-toxicity insecticides to avoid causing overall contamination.

2.1.3 Late-stage nutrient supplementation Biogas slurry nutrient solution is used for bag-cultivated edible fungi such as oyster mushroom, shiitake, enoki mushroom, white beech mushroom and bag-cultivated shaggy mane. For oyster mushroom, after every 2 to 3 flushes, it is directly injected with a water injector. Throughout the entire cultivation cycle of oyster mushroom, biogas slurry nutrient solution can be used, with simple operation, low input, few diseases and insect pests, and strong staying power. The yield is increased by 30% to 100% or even more compared with conventional water-type nutrient solution, and the products show characteristics such as thick caps, firm texture and good taste. For oyster mushroom, it is applied repeatedly by water injection after every 2 flushes; for shiitake, it can be applied in combination with water injection into the mushroom sticks; for bag-cultivated mushroom bags of white beech mushroom, enoki mushroom, king oyster mushroom and shaggy mane, it can be injected after the mycelium has fully colonized the bag and matured and before fruiting, or it can be used after one flush.

2.1.4 Formula of biogas slurry nutrient solution Adding appropriate amounts of lime, kemeling and some nutrients required by edible fungi to the biogas slurry stock solution can increase the yield by more than double, greatly increase the high-quality product rate, extend the fruiting period, give strong fruiting staying power, and significantly prolong the storage period of the mushrooms.

2.2 Technology for Applying Nutrient Solution in Bed-Cultivated Edible Fungi

For bed-cultivated casing edible fungi (button mushroom, shaggy mane and Agaricus blazei, etc.), fermented biogas slurry drawn from the discharge outlet of a biogas digester that produces gas normally and has been used for more than half a year is diluted with 1 to 2 times clean water to prepare a nutrient solution. It can be used continuously for topdressing with biogas slurry from the time the mycelium is fully colonized until the end of production. During the growth stage, each time the mycelium is topdressed, the nutrient solution can be directly and gently poured onto the surface of the mushroom bed; the bed soil must not be washed up, and then clean water is sprinkled once more. After the nutrient solution has infiltrated and the water on the surface of the mushrooms has slightly dried, cover with agricultural film to preserve heat and moisture. Afterwards, depending on the humidity of the mushroom bed, topdress with biogas slurry once every 7 to 10 d, and during the production stage topdress once after each flush is harvested. Using biogas slurry to topdress edible fungi is not only technically simple, with few diseases and insect pests and no residues, but also makes the mushrooms especially plump and strong. The number of fruiting flushes increases by an average of 1.5 flushes, and the yield is significantly increased, generally by more than 20%.

The test results proved that biogas slurry treatment can double the biological efficiency of wall-cultivated edible fungi, with a yield increase rate as high as 90.3% to 124.4%; the mushrooms are plump, large and glossy, and their marketability is significantly improved, clearly superior to commonly used production nutrients and water-type nutrient solutions. In addition, after treating the soil with biogas slurry and biogas residue, the number of high-quality "mud-crack mushrooms" in the middle of the mushroom bags increased significantly. Biogas slurry and biogas residue have yield-increasing, efficiency-enhancing and quality-improving properties in edible fungi production, and are truly pollution-free, low-cost, high-quality yield-increasing nutrients for edible fungi.

2.3 Soaking Method of Nutrient Solution

For all bag-cultivated edible fungi, after a period of fruiting production, when the yield declines or no mushrooms are produced, the mushroom bags, mushroom blocks, log sections, etc. are in a state of severe water shortage. They can be soaked in biogas slurry of a certain concentration, allowed to absorb enough water in the biogas slurry nutrient solution, and then taken out, until they recover to nearly their original weight. The biogas slurry soaking technique is especially suitable for bag-cultivated edible fungi with relatively few fruiting flushes, such as enoki mushroom, king oyster mushroom and white beech mushroom. When the yield of these fungi declines significantly or even no mushrooms are produced, soaking in biogas slurry can enable them to produce another flush of relatively high yield, which plays an important role in the production of some rare fungi. During soaking, to prevent the soaked objects from floating up, place the objects to be soaked into the nutrient solution pool and then press heavy objects on top. The soaking time should not be too long; for mushroom bags that have lost too much water, soaking can be carried out in several batches. Depending on the mushroom bag

water content, decide whether biogas slurry nutrient solution needs to be supplemented. Oyster mushroom and king oyster mushroom bags can be soaked in biogas slurry stock solution. After harvesting, bags of white beech mushroom, enoki mushroom, shiitake, etc. can be soaked at a concentration of 1:1 or 1:2 to supplement nutrients and continue fruiting.

3 Conclusion

Biogas slurry of a certain concentration used as a nutrient solution for edible fungi (base fertilizer and topdressing) has a significant yield-increasing effect, and can improve quality and advance the fruiting time. Compared with conventional nutrient solutions whose main components are chemical fertilizers, yield-increasing agents and hormones, the biogas slurry-based nutrient solution reduces cost by more than 80%; in terms of yield-increasing effect, compared with general edible fungi nutrient solutions, the yield increase rate is raised by 20% to 50%, and the high-quality product rate is increased by more than 10%. In specific application, compared with general water-type nutrient solution, the yield increase rate of oyster mushroom can be raised by 50% to 60%, that of white beech mushroom, king oyster mushroom and enoki mushroom can be raised by 20% to 25%, and that of button mushroom and shaggy mane reaches more than 50%. The high-quality rate of various edible fungi products is significantly improved, generally above 15%. After applying the nutrient solution mainly composed of biogas slurry, edible fungi have strong staying power in late-stage fruiting, the number of fruiting flushes increases by 2 to 3 flushes, and contamination and diseases and insect pests are significantly reduced. This not only lowers production cost (total cost can be reduced by 15% to 20%), but also enables sustainable development of edible fungi production.

Practice has proved that the components contained in biogas slurry are exactly the organic fertilizer components required for edible fungi cultivation, because biogas slurry comes from organic matter fermented by anaerobic bacteria in a biogas digester. At the same time, the liquid nutrients are comprehensive and rich, making it a low-cost, pollution-free, high-quality nutrient solution for edible fungi production. Using biogas slurry as the main component to make nutrient solution has lower cost and simpler operation than commonly used water-type nutrient solution; it uses less medicine, saves water and fertilizer, causes no environmental pollution, and edible fungi products can meet the requirements of organic food standards [.