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Influencing the ammonia content (NH3) during composting

You produce compost according to a fixed process. In phase I you make the compost, then you fill the compost into tunnels or maybe even the growing rooms. You steer the compost by adjusting the temperature and amount of aeration. But did you know that you can influence the NH3-content without adding anything to the compost?

During the conditioning composting stage, microorganisms in the compost breakdown the ammonia and lower the NH3content, as shown in the diagram below. There is a lot of micro life in the temperature band between 45 and 50oC. This micro life uses the NH3 as a source of nitrogen/nutrient source and converts the NH3 into different forms of nitrogen.

Ammonia (NH3) in phase I to destroy pests and diseases

When compost is being pasteurised, the compost and air temperature is kept between 56 and 60oC for eight hours in order to destroy pests and disease in the compost. These are not just killed by the high temperature, but also by the NH3-content. If the NH3-content is too low during pasteurisation, fewer of these pests will be destroyed. The optimal content varies for each tunnel company, but a general rule of thumb is: the higher the NH3-content, the greater the destructive effect. In my experience, the NH3-content at the end of pasteurisation is an average of between 300 and 600 ppm. After conditioning, some ammonia should still be released by the compost. If this is not possible, the contents were too high. (Attention! Getting the NH3-content right is easier said than done…)

Influencing ammonia content during phase II

At the end of phase I, the compost is filled into phase II tunnels. You assess the condition of the compost by smelling it. Your experience will tell you if the NH3 is lower or higher than usual. The HN4+-content will also confirm this, but this data is often only obtained once the tunnel has been filled.

Too high NH3 during filling can cause problems during the conditioning composting stage – it will take too long to rid the compost of NH3. Reduce the NH3-content of the compost as follows:

• use plenty of air when levelling the temperature in the compost

• lower the compost temperature to 45-46oC

• maybe open an air vent completely for 30 minutes

Do you smell less NH3 than usual when filling a phase II tunnel? Raise the NH3-content of the compost as follows:

• use as little fresh air as possible when levelling the temperature in the compost

• raise the compost temperature: higher than 53-54oC

The NH3 will then rise while the compost temperature is levelling out and at the same time ensure a higher NH3-content during pasteurisation.

Why does the NH3-content increase at high temperatures?

As the diagram shows, there is a lot of micro life below 50oC. This micro life absorbs the NH3 released by the compost, thereby reducing the NH3-content. At temperatures higher than 50oC  there is less micro life so that less NH3 is absorbed and converted. This means that the NH3-content will increase.

Bron: Mushroom Blog – Mark den Ouden

ammonia content (NH3) during composting

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