COMPOST 3
Good compost has structure
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?
This time: the importance of structure. By Con Hermans
AdVisie ‘de champignonteeltadviseurs’
hermans@champignonadvies.nl
T
he structure of compost plays an important role during various phases of composting and the subsequent cultivation process. ‘Structure’ is
often taken to mean the volume and springiness of the compost. A good indication of this is the bulk density per m3.
One of the aims of fermentation is to reduce the volume of horse manure and straw used as raw materials so the grower can fill the beds with a sufficient number of kilos of compost. Straw weighs less than 200kg/m3 and good quality horse manure not even 300kg/m3, but ulti- mately, at the mushroom farm, the bulk density of the compost should have been increased to around 500kg/m3.
Boosting the bulk density of compost is achieved on one hand by minimising and compressing the raw materials, and on the other by increasing the moisture content. Depending on the nature and quality of the raw materials, in some situations it is important to retain enough structure at the end of the process, while in others the focus is in reducing structure.
The right balance The structure is ‘good’ when the right balance is achieved between solids, liquids and air. When a compost has structure this actually means that the solid materials are layered in such a way that there are pockets of air. This is relative to the coarseness of the material, the softness and the shape. If there are enough air pockets, there is also enough space for water. This explains why you can use a higher moisture content with a high-volume compost, but have to drastically
reduce the moisture content when you have compost with a short structure.
Years ago in an experiment with artificial straw, I demonstrated how important the hollow struc- ture of straw is relative to the volume. See photo 2: In the glass on the left, the 100 round pieces of straw weighted down give a volume of 10 cm. In the glass on the right with 100 flattened pieces of straw, the volume is just 4.5 cm. To reduce transport costs, straw is today com- pacted into huge bales that can weigh up to more than 500 kg. To make these bales, the material is chopped and compressed, not leaving much of the hollow tube structure intact.
Photo 1: This straw still has enough hollow tubes.
14 MUSHROOM BUSINESS
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