A good climate control is of course vital for every mushroom grower even more if you want to stand out with the quality of the mushrooms. One of the most asked question I get as consultant is: How can we get better quality and how can we keep the quality of the mushrooms good until the end of the flush? Now, of course the quality at the end of the flushes will always be less than at the start, no illusions there. But improvements are always possible and most of that you can get from an ideal climate.

Before we had more advanced climate installations with more options, we always controlled the rooms on Air temperature, Relative humidity and CO2. However, with the new systems coming on the market there is a lot more to learn than we think and controlling rooms, especially in harvest stage, on moisture deficit, inlet moisture control and even measuring systems for evaporation are used.
To understand the difference between all the systems you need to know exactly what the Mollier Diagram stands for and if you manage to run the system well you will see advantages, especially in quality of the mushrooms. The Mollier Diagram is crucial in mushroom growing and climate computers make the changes in the room based on that Diagram with the Absolute humidity (AH) as the biggest factor. Let’s me explain a little bit more about of those controls, the moisture deficit.

As we are changing air temperatures in the flushes you will see in the Mollier Diagram that that will create differences in evaporation as we change the temperature but leave the RH the same, with other words, we change the AH. By controlling on moisture deficit we will maintain a constant evaporation, what will benefit the quality of the mushrooms, no matter what the temperature differences are. The computer will calculate the right RH for the current air temperature, to keep the same evaporation in the growing room.

Moisture deficit is the difference between the current absolute humidity in the room and the maximum possible absolute humidity at the same air temperature. Once this value is constant the evaporation capacity of the air is also constant.

To use this in a practical situation of course first of all you need a climate control computer that supports the moisture deficit system and change it from RH to moisture deficit control, in the computer that will be named as Absolut humidity control. Ideally this is linked with humidity control of the inlet air to get the best benefit. The mushrooms will have a constant evaporation and that will benefit the quality as changes in evaporation will disturb their growth. The mushrooms will get less water stems and go softer in a later stage what would give an extra picking days benefiting the yield as well as quality.

I recommend to change the computer 1 day before you start harvesting the flush from RH control to moisture deficit control. When you changed the control, set the AH in the computer so that the RH is at the same level as you normally run it in the flush. So if you normally run the flush on 17.5 degrees and 89% RH, keep the air temperature the same and set the AH so that he calculates the 89% RH as set point. Keep 0.2 difference between minimum and maximum AH. From that moment forward you let the computer calculate the right RH and change the air temperatures as you normally do, until the end of the flush. After the flush put the system back to RH control.

The only way to find out is try other controls to improve quality. Many option are out there and based on results on other farms worth trying. If you start and are seeing any improvement? Learn more and keep doing trials, good luck.

Erik de Groot
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