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COMPOST
Influence of ammonia during composting
Ammonia has a massive influence on the composting process. Without this substance making good compost is virtually impossible. However, an excess or shortage of ammonia can also cause serious problems. Many composters and growers underestimate the seriousness and do not measure the ammonia content well enough. Room for improvement!
By Jos Buth, Mushroom Advice Network Holland
josbuth@gmail.com
Regular ammonia (NH3) measurements are essential so you know what you are doing in the process.
Ammonia is produced by the nitrogen products that are added to straw. The most common nitrogen products used in mushroom growing are from organic sour- ces, such as chicken and horse manure, but chemical sources such as urea and ammonium sulphate are also used. Liquid manure is water that contains nitrogen, which in turn produces ammonia. Ammonia occurs as a gas (NH3) and as a solid (NH4). It is formed as the compost heats. Ammonia is already produced at temperatures above 53 degrees Celsius (increasing concentration of ammonia as compost is heated up before pasteurisation). The higher the compost temperature becomes, the more ammonia is formed. Interestingly enough, above 80 degrees Celsius, the ammonia molecules disintegrate and the ammonia changes from its solid form NH4 into the gas NH3. Above 80 degrees it is striking that very high ammonia concentrations can be measured, particularly when composting is taking place in a closed system (in special phase I tunnels). At above 80 degrees, phase I compost in tunnels can produce 10000 to 12000 ppm NH3, which is a typical reaction to a chemical process.
Changing legislation Ammonia makes the compost soft and less greasy. Sof- ter compost also contains more locked-in moisture. An optimal process in phase I will give the compost a dis- tinctive caramel aroma, the typical ‘good’ odour known to all experienced mushroom growers. It is the odour you can still smell after a shower in the evening on the day you have filled a tunnel or growing room with fresh compost. This odour can be offensive to people other than growers, so in countries like the Netherlands and Belgium composting is only permitted in indoor faci- lities to prevent odour nuisance caused by NH3. I am sure it is only a matter of time before other countries follow suit. In Canada, for example, companies are being put under pressure to move their composting operations indoors. In British Columbia in the west of Canada, indoor composting has been introduced recently, which has stepped up the pressure on Ontario, in east of the country, to make the change too. An in- door composting plant has also been built in California, and legislation in Poland is starting to change as well. In Poland, growing numbers of companies are taking amended legislation in the not too distant future into account. In Australia, a new indoor composting project is in the pipeline, which can also be seen as a sign that legislation there is about to change.
Too high ammonia concentrations When is the ammonia level too high in the compositing process? If a grower is unable to rid the compost of ammonia within the normal time this may indicate an excess of ammonia. This is usually caused by too much chicken manure in the mix. Too wet, but also too dry, compost can also present ammonia problems. Equally, a too high compost temperature during pasteurisation, which destroys too much bacterial life, can contribute towards not being able to rid compost of ammonia (in time). This is not only disruptive for the cropping cycle, but also dehydrates the compost too much, as it takes
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