Compost activity: a question of balance

Mushroom growers the world over share the same problems. At certain stages during cultivation there is more or less compost activity than wished. This situation can arise immediately after filling or during cooling down. But a rapidly rising compost temperature during the first flush can also be very damaging to mushroom quality. A few things to look out for….

By Jeroen Van Lier, C point

On most companies, compost activity is well managed, but each grower must discover the optimal formula for each individual situation. Rather like finding perfect balance. If too much weight is placed on the left side of the scales, you have to adjust the right side as well to preserve the balance.

Filling the growing rooms

It all begins when the growing rooms are filled with compost. There are a couple of aspects that must be paid attention at the very start.

Humidity content and compost structure have a big influence on the activity level a grower can expect after filling. Dry, highly structured compost will be very active immediately after filling. To obtain the required amount of kilograms per square metre, more of this type of compost must be used. This extra thickness is mainly due to air, which works as a heat buffer.

Once the compost is active, this air is warmed up and is very difficult to cool down. The most effective remedy is to apply water during or immediately after filling, and to compact the compost as much as possible. Wet compost, with little structure variation, should be treated in the opposite way; fill it lightly compacted and give water sparingly or not at all.

Incubation

If all goes according to plan during incubation, the first signs of activity can be noticed about 9 days after spawning. This activity increases as incubation continues.

On the 15th day after inoculation the compost should be fully colonised and activity will decrease.

If circumstances force the grower to case the compost early or remove it from the tunnel, activity will continue in the growing rooms. Activity is very difficult to control at this stage as the casing soil on the compost acts like a heat-retaining blanket.

In this case the grower must keep the air temperature in the growing room very low to maintain a compost temperature of 26 degrees Celsius. The casing soil will cool and the mycelium will not grow any further in the casing soil.

This explains why it is better to apply casing soil later; otherwise the required effect in time gain will be counteracted.

Supplement

Supplements encourage extra activity in the compost. How much activity depends on the type and amount of supplement. Normally growers can use 15 kilograms of supplement for each 1000 kilograms of phase 3 compost. Research has shown that this ratio gives an optimal result, although it remains compost-dependent. If the compost has a high nitrogen content then 15 kilos can already be too much.

Supplementing is the ideal way to get more and better quality mushrooms, but only if the compost is completely free of infections from competitor moulds.

If compost is infected, the supplement will have a negative effect on the compost, as the supplement acts as a nutrient medium for the competitor moulds (see photo). These will in turn damage the mycelium or mushrooms during cultivation, and reverse any positive effects of adding supplements in the first place.

Filling weight

The filling weight also determines activity, as well as being a crucial contributing factor to the total amount of mushrooms a grower can harvest.

A general rule of thumb is that if you fill 10% more compost, you can expect 10% more mushrooms. This is quite reliable, but the climate control system must be able to cope with extra amount of compost.

So we return to our original idea of the scale; can we return balance to the scales by managing the extra activity? And if yes, what does that supply in extra yield?

Finding the right balance

It's plain that the sought after but potentially disruptive compost activity depends on many factors. Literature is full of references to figures indicating the ideal filling weight, but in practice it varies from situation to situation. Discovering the ideal proportions for well-balanced compost activity is the challenge facing each grower.