40
COMPOST
An aerated fl oor is needed to fully optimise the compost quality.
the dose is not extremely high, more advantages can be gained than if no water is added at all.
Moisture managment during phase III The water balance during phase III is strongly affected by the system used to encourage mycelium growth in the compost. For quite some time, many turnkey plants have placed a cooling unit behind the inlet filter as a way of lowering the purchase costs. This works well on most companies, but in Spain experience has shown that with an average, low outdoor humidly (up to 15%) and an outside temperature of around 40 degrees Celsius, the compost dries out too much if outside air has to be used for cooling – because of the position of the cooling unit. Another approach used by many tunnel companies is placing an automatic cold air humidifier underneath the tunnel floor to compensate for any excessive evaporation and to avoid heating the air temperature unnecessarily if there is a cooling demand. A tunnel filled with compost of varying moisture levels during inoculation also has negative effects. The first or last metres of a tunnel are often drier or wetter than the rest during inoculation. This is usually because these parts of a tunnel are filled too loosely or too tightly packed. After correction, the space after the first metres in the tunnel is usually filled more loosely, but correction is required again as the end of the tunnel approaches so the compost is squeezed to make sure the right amount is filled. If there is not enough compost the structure
A good method is to loosely pile the compost into windrows while it is being wet on the day before the tunnels are fi lled.
will be more airy and the layers will be smaller, while the opposite applies if there is too much compost. In this case, the filler tries to cram all the compost into the tunnel which results in an over-compacted layer of compost that is often higher than in the rest of the tunnel. Retaining boards that are too short also have a negative impact. Obviously, a process on an open floor is more susceptible than on a spigot floor, but do not fall into the trap of thinking that a process on spigot floors is free of this potential problem.
This photo shows the spraying system which has been mounted in a pulling winch so that extra water can be sprayed during inoculation and when emp- tying the spawn run compost.
Evaporation during cultivation A compost that is more densely compacted during filling will hold more water than compost that has been filled more loosely. Compacted compost also has lower activity as less insulating air is left behind in the compost after filling. Filling phase III offers clearer ad- vantages than filling phase II compost, as growers who complete the colonisation stage in their growing rooms cannot correct the moisture content as well as growers who use phase III compost. In mushroom growing, cor- rect evaporation at the various stages of development is critical for an optimal process. Evaporation ensures the heat released by the compost is transported away, so that – with sufficient evaporation -the compost temperature falls while the mycelium is developing. Compost that is too dry will therefore be more difficult to manage during mycelium growth, but also after casing, during pinheading and during harvesting. Evaporation while the pinheads are growing stimulates a flow of fluid that transports moisture from the com- post in the casing soil to the pinheads and mushrooms to evaporate. This is a natural process whereby the osmotic pressure of the compost also plays a role. Osmotic pressure pushes water via the mycelium to the pinheads and the grown mushrooms. This sap flow also supplies nutrients (protein) to enable mushroom growth. So, compost that is too dry can result in consi- derably reduced production simply because the vital flow of fluid stagnates. The drier the compost, the lower production will be. Too dry compost will also extract too much moisture from the casing soil. On the other hand, too wet compost will reduce activity, certainly if the compost has a short structure – and a less active compost will not make cultivation any easier. In brief: getting the moisture balance right is vital to successful production! ◗
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