The deterioration in quality during the last two flushes is often surprising. In many cases this is caused by mushrooms maturing instead of actually growing. Moisture management is an important aspect here. A sufficient and - particularly important - constant moisture level in the casing soil is essential for good quality mycelium. This mycelium is the transport medium for the nutrients required for the second flush.
If the casing soil dehydrates too much during the first flush the mycelium will become too thready and no longer able to transfer the nutrient flow to subsequent flushes. It's extremely difficult to recover a good moisture level for casing soil that has been allowed to dehydrate during a flush.
Sprinkling little and often and adding water over a two-day period can help to limit the damage but will not aid full recovery. Changing the moisture management system by using coarser casing soil increased sprinkling during the preparation stage and the first flush, reducing the cooling a little using slightly higher CO2 values with cold dry weather circulating a little more with a relative humidity of 1-2 percent higher etc., are all measures that contribute to a better moisture balance.
Jos Hilkens, AdVisie ‘The mushroom cultivation advisors’