Controlling the growth of mushrooms in conditions of nutrition

Biuletyn Producenta Pieczarek PIECZARKI 4/2015 s. 16-23

Providing mushrooms with resources needed for the expected yield, or the substratum and casing soil and sufficient quantity and weight of the spawn does not automatically mean the possibility of obtaining high yields, even if we have sufficient technical conditions to maintain microclimate conditions required for its growth and development. The wide variation in yields and not achieving their maximum size in relation to available resources is a fact. This means that we still do not really know how to control the behavior of the mushrooms. This is the second problem necessary to solve in order to achieve the intended objective of getting yields of 40 kg/m2 in three flushes. The issue of controlling the nutrition of mushrooms turned out to be much more difficult than expected at the time of acceding to build technology based on it. The current system of microclimate control in the cultivation hall turned out to be not fully useful to obtain stable yields and required development of new rules to ensure control of the behavior of mushrooms (in particular evaporation). Our knowledge about the causes of the variable behavior of the mushrooms during growth is also not full.

Controlling includes three major processes described below.

Recolonization of substratum after sowing feeding supplements. The purpose of controlling is to prevent hyperactive behavior of the substratum and to assimilate the mushrooms with introduced to the substratum feeding supplements. Achieving this goal is the first necessary condition to obtain the planned level of yield. Breakage of spawn in an overgrown substratum interferes achieved during growth balance between it and the thermophilic organisms (Scytalidium). This is due to the fact that – after breakage of the spawn and disengagement of the substratum during removal from the growth tunnel – between the straw there is more oxygen than before disengagement. Once incorporating therein a quantity of water necessary to balance the dose of feeding supplement, and as it has a high temperature, it causes multiplication of these organisms. This results in a rapid increase in heat and even faster proliferation of thermophilic organisms, while inhibiting the activity of mushroom spawn. If this rise is not interrupter before the temperature reaches over 32°C, it is life-threatening for spawn or significantly weakens it. Although the substratum is cooled intensely, by reducing the air temperature and increasing its movement, the balance between spawn and thermophilic organisms cannot be generally restored and to complete the second flush the cultivation is done over large temperature differences between air and substratum. This means that the shock is much more difficult to carry out and it is also hard to control transition to the second flush when the temperature of the substrate is high and tends to rise from the middle of the first flush. The fruiting bodies of the mushrooms are subjected to excessive evaporation of water from them, and thus the yield is reduced.

Please note that adding feeding supplements to the substratum requires an additional amount of water required in the digestion (broken spawn colonizes the substratum once again and digests the feeding supplement with enzymes until the end of the shock) and transportation of nutrients to the fruiting bodies. This requires the development of a program of pouring water into the substratum. This program is modified depending on the season, humidity and behavior of the compost.

Keep in mind that the cultivation of mushrooms on substratum with excessive activity requires a different approach to control its growth.

Transpiration – evaporation of water from the surface of the fruiting bodies, which determines the rate of their growth. The aim is to obtain the maximum weight while keeping the characteristics of fruiting bodies typical of the breed cultivated throughout the harvesting season. Mushroom do not have any slits in its rind, which means that the rate of evaporation of water from its surface (in accordance with the process of transportation of nutrients) depends mainly on the parameters of the microclimate and the temperature of substratum. Both too fast growth of the fruiting bodies and too slow worsen their welfare, its quality and weight. This is due to disturbance of the balance between the collection of water from the casing soil and the substratum, transport of nutrients and growth of the fruiting body weight (number and mass of cells and cell membranes). Transpiration may be too fast or too slow.

  • Too rapid evaporation makes the fruiting bodies lightweight, flat (Fig. 1 and 2), with the husk, prematurely stretched membrane and is often accompanied by shafts that are cracked inside. The result is a loss of weight of fruiting bodies, and thus the yield. Fruiting body with a diameter of about 4 cm (fig. 3 and 4) having the same volume can vary the weight from 40 to 25 g. Assuming a standard of 35 g, this means a large drop in yield, up to 25% with the same amount and the same size of fruiting bodies collected. This decline intensified since mid-flush collection. The appearance of light fruiting bodies, without changing of their shape does not necessarily mean that every time the reason for this is excessive evaporation. This may also be a result of water deficit in the substratum. This also happens when using dry substratum produced during the high summer temperatures. Then the watering will result in a return to the standard weight.
    Loss of water is easy to tell by observing the volume of fruiting bodies in a standard box of 2.5 kg. It can be filled in the middle (heavy fruiting bodies) in the first days of harvest of the first flush, and in following days full when fruiting bodies are lightweight and despite of this fact they have the same weight. Weight of fruiting bodies should be monitored regularly during harvest.
  • Too slow evaporation is causing greasy stains on the fruiting bodies, their growth is slow, skin is pink and yellow and there are dark rings in the stalks from which it is easy to squeeze out the water.

The current evaporation control system is based on measuring the relative humidity but it is imprecise; always indirect. The assumption that the relative humidity reflects the evaporation of water from the surface of the skin (transpiration) does not work in practice. The amount of water that can be introduced into the air, is determined by water deficit. It is not identical with the evaporation of water from the skin surface of the mushrooms. Therefore, a proposal to introduce the term „transpiration” in relation to release of water vapor by mushroom is made as opposed to evaporation of water in the casing soil or floor covering. From the standpoint of cultivation transpiration is essential.

Factors that determine the course of transpiration, are as follows.

  • The deficit of water in the air in the cultivation hall. It is described also as the relative humidity or water content in the air and read from the Mollier chart. The higher it is, the greater the evaporation is.
  • The air temperature. With the increase in air temperature transpiration increases.
  • The movement of air. Transpiration increases with increasing air speed over the fruiting bodies.
  • Atmospheric air pressure. The higher it is, the smaller the evaporation.
  • The amount of fruiting bodies and growth rate of their weight on the shelf; skin surface of all fruiting bodies. The higher it is, the higher the amount of water evaporated. Traditionally, it is advisable to increase or decrease the air changes depending on the number of fruiting bodies on the shelf.
  • The temperature of the substratum. As the temperature is increasing and the difference between the temperature of the air and the substratum is greater, the evaporation of water is greater. Differentiation of activity of substratum during the cultivation in Poland is very significant. This translates into the rate of evaporation of water from the fruiting bodies and the casing soil and the rate of growth of fruiting bodies. The current system does not include this parameter.

The problem complicate even more when we change several parameters at the same time.

Figure 1. Fruiting bodies growing at an excessive transpiration
Figure 1. Fruiting bodies growing at an excessive transpiration
Figure 2. Fruiting bodies growing with proper transpiration
Figure 2. Fruiting bodies growing with proper transpiration


Figure 3. Fruiting bodies before harvest
Figure 3. Fruiting bodies before harvest
Figure 4. On the scale
Figure 4. On the scale

The process of control is based on:

  • maintaining the water content at a certain level (usually it is 12 g, and the range varies from 10 to 14 g),
  • maintaining a constant air movement on such a minimum level at which the air conditioner is running smoothly and there is a movement over all the shelves,
  • air temperature changes during yielding period, mainly being increased to maintain the desired water content in the air (range from 17.5 to 21°C),
  • maintaining the desired relative humidity of the air that is based on the Mollier chart for the particular water content in the air,
  • changes of concentration of carbon dioxide (from 2000 to 7000 ppm) during yielding in order to maintain the required level of water content in the air while minimizing its movement,
  • maintaining the lowest possible air humidification in the tunnel, using watering devices installed under shelves or along the side walls.
  • maintaining percolation of water from the substratum to the casing soil.

Although control of these parameters does not always allow to achieve the desired effect in the behavior of fruiting bodies. This is due to the fact that the amount of evaporation (transpiration) is assessed indirectly.

The current control system of growth of mushrooms is based on the principles of evaporation of water, in our case with the wick of a dry-bulb thermometer. Hence the search for methods to assess the actual evaporation. One such way is to use evaporometer. For this purpose, an attempt was made using 50 g mechanical postal scale (Fig. 5 and 6). This allows to capture the moment when evaporation is blocked, as indicated by no loss of water weight, or the point where evaporation is too fast. The amount of water evaporated will depend not only on the chosen parameter values, but also on the surface of the pan filled with water.

We are currently working on determining the correct size of evaporation, watching both its size and behavior of the pins and fruiting bodies. In addition, observations are used of pace of drying floors and weight loss of fruiting bodies and appearance of the husk. Currently, it is assumed that evaporation should equal 1g over 12 hours from an area of ​​200 cm2. This issue will be returning in the future. The tests used Piches evaporometer.

The location of measurement of the parameters of the air in the cultivation hall is of significance too. At low air movements the difference in the reading of wet and dry thermometers traditionally placed in the hall and  measurement of the same parameters two centimeters above the fruiting bodies, pins or spawn reaches 20°C,  depending of the increased air movement. This means that a significant difference in measuring relative humidity.

The domination of pins. The aim is to obtain the desired density and number of generations of pins in each successive flush. The principle is that all buds are formed during shock and released in each successive flush. They are differentiated, meaning creation of generations, in accordance with the principle of diversified growth of younger and older pins and of stronger and weaker. In other words, they are differentiated by their so-called periodic arrest and release. In the first flush to adjust the density and the amount of generations initially by a shock, and after the formation of a pins differentiating microclimate conditions inhibiting the growth of weaker and smaller pins, keeping the growth of the oldest and largest (Fig. 7). In this article I’m not interested with the issue of controlling the shock, since the outcome is more dependent on experience of the person handling the shock than the process of nutrition. What facilitates replication of its course is the use feeding supplements into the casing soil. In the transitions between the flushes the process of releasing pins is also depends on other factors, of which the most important are listed below.

  • Harvest. Only conducting a selective harvesting and preventing the closure of shelf space by fruiting bodies allows for a gradual release of pins from the middle of the flush practically without interruption or with only a one-day break between harvesting of another one. Closing the shelf will reduce and delay the next flush of the fruiting bodies even up to three days, and significantly reduce the harvest period, notably during the second flush.
  • Microclimate conditions. Raising the temperature in the air and the substratum; renewal of this activity causes the released pins to
Figure 5. Post scale as evaporometer
Figure 5. Post scale as evaporometer
Figure 6. Writing down the changes of water loss
Figure 6. Writing down the changes of water loss

grow simultaneously. After completing a flush it is unadvised to change the microclimate parameters to ensure constant evaporation of water from the surface of the casing soil and its transpiration of pins, supported by a large periodic variation in carbon dioxide from 2000, up to as much as 10,000 ppm, limiting and accelerating air movement.

  • Watering. Direct watering after harvest causes the simultaneous release of the pins. Therefore, it is advisable to make one dose of water when pins are varied, for example one or two days after the completion of harvest.
  • Salinity of the casing soil. At high content it permanently reduces bonding in each flush. But this kind of salinity of casing soil is not found in Poland. It has to be induced artificially and is used primarily in the cultivation of portobello mushrooms.

It is important in the process of mushrooms nutrition to maintain a constant gas exchange between the substratum, the casing soil and the air in the cultivation hall and maintenance of percolation of water from the substrate to the casing soil. Constant evaporation of water from the casing soil significantly stabilizes the microclimate in the cultivation hall.

Knowledge of the process of nutrition and controlling it is the foundation of effective course of growth and developing one’s own technology.

Figure 7. Improper transition between the first and second flush
Figure 7. Improper transition between the first and second flush