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Filling in several layers will benefit the filling quality.


longer to get the compost free of ammonia. Patches of compressed compost in the tunnel can also cause problems with ammonia. In the latter case, growers would do well to lower the average compost tempe- rature at the end of the conditioning process from 48/47 degrees Celsius to 45/46 degrees Celsius. In an emergency situation, an average compost temperature of 44 degrees can also be a solution, but remember that this value comes dangerously close to a non-optimal temperature zone. Compost temperatures below 43 degrees stimulate the activity of weed moulds. The effect of the lower compost temperature is a higher temperature in patches of wet compost. At an average compost temperature of 48 degrees, the temperature in a wet patch may be 52 degrees or higher. Ammonia will not be broken down above 52 degrees. And in fact, more ammonia will be produced at temperatures of 53 degrees and higher. So optimal filling is essential. A spinner on the fil- ling line to the filling cassette will give a more open structure, which leads to better aeration. Many growers think that using a spinner in this phase of the process will damage the structure too much, but experiences in the USA show that structure damage caused by a spinner in the tunnel filling line is negligible. In the USA, far more homogenous compost temperatures are achieved after a spinner has been installed on the transport belts that convey the compost to the filling cassettes. Do pay attention that the person doing the filling has been properly instructed about how to fill a tunnel optimally. Explain how serious the consequen- ces on the further process are if the tunnel is not filled optimally. For example, it is very important to keep the distance between the end of the supply belt and the compost already in the tunnel the same at all times. The speed of the supply belt can compress the compost too much if the distance between the belt and the compost in the tunnel is too short. A short-structured compost combined with watering when the tunnel is being filled will be detrimental to optimal aeration, as giving water during filling leaves too much unabsorbed water in the compost. If water is applied on the day prior to filling, the compost has the chance to absorb this moisture - which benefits good aeration. Too much ammonia also has other major disadvanta-


ges. If the ammonia concentration rises too high (above 700 ppm) during phase II, too much microlife will be destroyed. Sufficient ammonia together with a good pasteurisation temperature (higher than 56 degrees) destroys weed moulds, but if the ammonia concentrati- on is too high during phase II useful and vital microlife, needed to convert the ammonia to protein, will also be destroyed. High ammonia concentrations during level- ling are just as harmful as high concentrations during pasteurisation. Chemical nitrogen products such as urea can produce a lot of ammonia in a short time. Ammonia produced by chemical raw materials will also easily disappear after a lengthy period of copious aeration. Substances such as urea are aggressive and fundamentally attack the compost. If urea is not dosed too late during phase I, and providing the concentration is not too strong, you should not experience any problems with ammonia during phase II. Urea is often dosed to accelerate the rise in compost temperature during phase I and to boost this temperature rise. However, this indicates that there is something wrong with the recipe, the blend or the raw materials used.


Compost temperatures above 80 degrees Celsi- us with sufficient oxygen produce extremely high concentrations of ammo- nia in gas form (NH3).


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