By Mark den Ouden, Mushroom Office |
mark.den.ouden@
mushroomoffice.com COMPOST
Straw can make or break mushroom quality
You might ask what compost quality is. Ultimately, it's all about the production and quality of mushrooms. Compost is made of waste resources, the most important of which is straw. In West Europe, we use stable bedding that comprises horse manure -or droppings -and urine. The main ingredient however is straw.
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If the straw is not decomposed well enough, the
mushrooms will have insufficient acces to the nutrients.
ompost is often assessed for pH, nitrogen, C/N ratio and moisture content. But are these figures really important? Logically, they have to be within a minimum and maximum range. But what if you wonder which is a better nitrogen percentage: 2.0 or 2.5? In practice, you see good production on both percentages, but also very poor yields. This applies to this data obtained from laboratory analysis. So, what actually determines the quality of the compost?
Water absorption ‘The moisture content of the spawned compost must be somewhere between 61 and 64%’, is the answer many mushroom growers would give to that question. Basically, I agree. But actually I think how much water the compost can absorb is more important. I sometimes see compost with a moisture content of 61% that you can apply water to, but it still feels dry. And when you look at the floor you see brown water (photo 01). Conclusion: the compost is not absorbing the water. If the compost does not absorb water, you will usually notice that it has much more activity. Water conducts the heat from the compost. If compost does not absorb water, it will have more difficulty in releasing that heat. This will trap you in a vicious circle. The higher activity causes the compost and casing soil to dehydrate even more. This has a negative impact on the quality and yield of mushrooms. Water makes up 92% of a mushroom. If there is not enough water in the compost, the mushroom cannot absorb enough either.
Mycelium growth
Another indicator of compost quality is myce- lium. In a tunnel, the compost looks nicely colonised with mycelium. But take a handful of
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compost and rub away the mycelium and you will see yellowish, shiny blades of straw (photo 02) . The compost is not sufficiently decomposed, and the mycelium cannot grow through the straw. This also prevents it absorbing nutrients from the straw. The compost feels prickly, the straw is not ‘soft’. (photo 03)
Even in this case, analysis will not reveal any major discrepancies. Everything seems ok, the mushrooms at the start of the flush look good, so as a grower you will tend to think: ‘There's nothing to worry about’. But as the end of the flush comes into sight, the quality and the yield will be disappointing. In the second flush you will see more uneven emergence of the mushrooms (photo 04), and in the third flush sometimes even bare patches with no mushrooms at all. So appearances may suggest a wet compost, but in fact the moisture has evaporated in a day. The water mainly surrounds the particles of straw and cannot transport any nutrients to the mushrooms. If the straw is not decomposed, and the mycelium grows around the straw, the myce- lium cannot extract any nutrients from the straw, and, consequently, the mushrooms will have insufficient access to nutrients too. If the waxy layer around the blades of straw is left intact, the straw cannot absorb and release enough moisture. In my view, this not only affects the moisture content of the compost, but also the nitrogen content that is bound in the water. In other words, there is a scarcity of water during mushroom development and growth, but also a nutrient deficiency in both water and straw.
Straw
Straw is the most important component of com- posting. All the other aspects have to be correct, but the most vital element is straw. Straw creates structure in the compost, provides nutrients and
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