COMPOST 2
Good compost needs good nutrients
Compost is the foundation that supports cultivation and represents 85% of the power behind mushroom production, so it goes without saying
that good compost is vital. But what actually constitutes good compost? By Con Hermans, AdVisie ‘the mushroom growing consultants’,
hermans@mushroomconsulting.nl
G
reen plants can create their own sugars and convert the nitrogen absorbed from soil into amino acids and proteins. During the growing season, applying an extra dose of fertiliser can stimulate this process. With mushrooms, the reverse applies, mycelium obtains its nutrients by degrading sugars and proteins, so these nutrient sources must already be present in the compost before the crop starts to grow. It is up to composters to ensure these nutrients are in ample supply when they deliver the compost to the growers.
In the past, each composting company had its own recipe and a wide variety of organic matter was added to the straw or horse manure, such as cotton seed hulls, bone meal, blood meal, rape seed, lucerne, urea and brewer’s grains. It was often supplemented with a range of elements and trace element such as superphosphate, potassium sulphate, copper, zinc, manganese and iron.
Later on, it became clear that there were already copious amounts of these elements and trace elements in chicken manure, so adding extra was unnecessary. This simplified and standardised compost recipes. Many recipes are now formulated around a basis of straw or horse manure as the source of carbon (C), with the addition of chicken manure as a source of nitrogen (N), whereby the aim is to achieve the optimal nitrogen percentage, or better said – the correct C/N ratio.
Fermentation During the composting process, the basic raw materials must be transformed into easily accessible nutrients for the mushrooms. This process is partly chemical and partly biological. The protective wax layer surrounding the straw must be broken down, the easily degradable
20 MUSHROOM BUSINESS
carbon must be fermented and the ammonia must be converted into amino acids and proteins. This creates a so-called selective compost, which contains as few as possible nutrients for com- petitor moulds, but is favourable for the rapid growth of mushroom mycelium which can then build up an advantage on the growth of these competitor moulds. During fermentation and pasteurisation, up to 40% of the organic matter is expended, which causes the compost temperature to rise to the requisite 80 degrees Celsius during fermentation and 60 degrees during pasteurisation. It is impor- tant not to over-ferment, as this will remove nutrients that could otherwise be utilised by the mushrooms. The result may well be attractive, black, well-fermented compost will less sen- sitivity to competitor moulds, but this type of compost is also more nutrient-poor and will lack the necessary activity later in the cropping cycle. Rough speaking, in situations where there is greater sensitivity to competitor moulds and the hygiene conditions are more difficult to manage, a lengthier fermentation is necessary to be on the safe side. Under other conditions, you can reduce the fermentation process and retain more nutrients in the compost. During fermentation, more carbon than nitrogen will vanish from the compost so the compost becomes relatively richer in nitrogen, thereby lowering the C/N number.
Good quality straw is pro- tected against mould by a natural wax layer.
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