the compost as little as possible. However, if you meas- ure on the filling machine, what you see is soft compost, totally lacking in structure, flowing from under the chain with a volume of just 25 cm, for example. And if you measure after the levelling and pressure rollers the same compost is compressed further to a thickness of 19 cm. We should apparently adjust our filling machines to ensure that less pressure is applied to the compost. It is more difficult to avoid compaction in blocks. This compost always has to be compacted to a certain extent to create the blocks in the first place. On top of this, additional pressure is exerted on the blocks at the bottom of the pallet during transport. Afterwards, these are precisely the blocks that produce the least. You can recover some of the volume lost during transport by knocking the blocks against the floor before they are placed in the shelves – rather like plumping up a cushion.
CAC
CAC is used to get the timing of the flush right, for uniformity and to compensate for too heavy casing soil. A condition is that enough CAC material is used. Many growers express the amount of CAC in grammes of com- post per m2
in the preparatory stage, while others can happily apply 58 litres. At filling, growers must be able to decide whether the compost needs more water, or whether a more sparing spraying regime should be applied than normal.
on how much water should be applied on a farm as the variations in cultivation methods and conditions are just too wide. Some growers are content with 8 litres/ m2
A rule of thumb is that when compost has less volume, you should always be cautious with spraying, and that for every percent that compost differs from the normal moisture content, you can correct this by adding about 3 litres/m2
to the basic quantity.
. This is not however a good indicator, as the effect of CAC is governed to great extent by the number of inoculation points mixed through the casing soil. In well-fermented, fibrous compost you mix far more inoculation points through the casing soil and myce- lium will grow from every piece of fibre. With coarser, less fermented compost there are a limited number of sprigs of compost, a great deal of these will produce nothing anyway as the mushroom mycelium has only coated these particles superficially. It is better if grow- ers estimate how much CAC is needed at the moment the compost is filled – but that is no easy matter. The volume of the compost gives a good indication. Greater volume usually implies there are more harder pieces of straw, so you therefore need more CAC to create the same effect.
Moisture content
Mushroom production may well be related to the kilos of dry matter filled per m2
, but water makes up 95% of
a mushroom, and the mushroom obtains that water mainly from the compost. This water also transports nutrients from the compost up to the mushrooms. So, the compost must contain enough water. A basic amount of water is supplied along with the compost. Logically, as at the moment of inoculation the compost has to be wet enough otherwise no good myce- lium growth will take place. However, during mycelium growth, the compost loses part of the water it holds again. It is impossible to make sweeping statements
It is also import to distribute the water well throughout the entire compost layer. The upper layer of a soft compost has a tendency to soak up moisture like a sponge, which creates a weak contact layer between the compost and the casing soil. In a highly structured compost on the other hand, water will tend to sink down to the base. A small amount of water on the net is not an immediate problem, but a few centimetres deep and this layer of compost will be unable to release any nutrients. Spraying water on incubated compost during filling is the best way to achieve even distribution. This means that well-incubated compost is essential.
A costly mistake Compost production must have a competitive cost price so waste materials are usually used as the raw materials and the tunnels are filled to maximum capacity. Any changes made at the composting facility to produce better or more stable compost, for example, introducing more structure, making it richer in nitrogen, more fermentation, a lower filling weight or longer mycelium growth period, will always add to the cost price. Compost represents a considerable portion of the total cost price of mushrooms for growers, but making savings on compost and compromising quality is the wrong decision. Bad quality compost is always going to be an expensive decision, so how much more should you be willing to pay for good quality? This depends on a number of things, but a 10% higher compost price is usually completely covered by giving around 3% higher production.
I hope that composters and growers do not base their operational strategies and negotiations entirely on cost price in the future, but rather devote more attention to quality. If you review all the previous articles in this series you should know what good compost involves and what you should be producing as a composter, and as a grower you should know what to ask for - stable, well-incubated, selective compost with enough easily decomposable nutrients and structure for a good moisture/air balance.
MUSHROOM BUSINESS 37
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