Organic matter and ash


Compost consists of water and dry matter, the latter of which can be divided into organic mat- ter and ash. During the fermentation process, the combustion of organic matter increases the ash percentage in the compost.


Mushrooms grow on this organic matter, and not on the ash. There is a direct link between the amount of available organic matter and mushroom production. Fermenting compost for too long results in less organic matter, more ash and in the end fewer mushrooms. If the compost has a high ash content, it has by definition a low organic matter content. A high ash content is not only a result of fermenta- tion - maybe more ash was added in the form of gypsum or raw materials with higher ash contents. For example, half of the ash originates from the added gypsum. But the ash content in chicken manure, for example, can also vary widely. I come across chicken manure with an ash content of 12%, but also with 36%. The extent of fermentation and the type of raw materials used can bring about large differences in ash contents. I have seen incubated compost containing 20% ash, but also 38% ash. That difference, however, means that one type of compost can contain 30% more organic matter than another, and therefore has higher produc- tion potential.


Nitrogen content


The percentage of nitrogen is often used as an indicator of the richness of compost. Although we know that mushrooms can only absorb a small amount of nitrogen from the compost, experience has taught that compost with a higher nitrogen content gives higher production. Even so, do not compare one compost with another based on nitrogen, as this can lead to the wrong conclusions. The nitrogen should be seen in relation to the carbohydrates. Mush- rooms need both of these, and they should be in balance. If there are too many carbohydrates, the nitrogen will not be utilised properly, but if there is too little nitrogen, the carbohydrates will be exploited insufficiently. See it this way: to build a house efficiently you need to harmonise the number of bricklayers (carbohydrates) and the number of bricks (nitrogen), you have to have both in the right ratio. Each organism has a specific, optimal C/N ratio of nutrients that it needs for optimal growth. In mushroom growing terms, a rich, incubated compost is one with a C/N ratio of around 13, which means 13 times more carbohydrates than nitrogen. This C/N number provides more accurate information than the N percentage often used as a parameter to assess compost. This is explained by the fact


What is good compost? Compost is the key decisive factor in mushroom production. Growers in some


countries can still achieve excellent production under relatively primitive condi- tions providing they use good quality compost. Anyone can cultivate mushrooms on good compost, they virtually grow themselves powered by the driving force of the compost that stimulates growth and maintains evaporation levels. Mastery of the true art of growing only becomes apparent on inferior quality compost. Rigidly following standard procedures or letting a computer dictate the pro- gramme will cause production to plummet. Growers must therefore ensure they fi ll their growing rooms with good compost. But what is good compost? In a series of articles, Con Hermans will be examining a number of important aspects that infl uence compost quality and how this in turn impacts on produc- tion.This second article on the subject focuses on nutrients in compost. Future articles will cover subjects including structure and moisture.


A compost recipe developed in England 65 years ago.


“The C/N number provides more accurate


information than the N percentage often used as a parameter to assess compost.”


that nitrogen is calculated over the dry matter percentage of the compost and C (carbon) as a percentage of the organic matter. The ash percentage also has a significant influence on the optimal N percentage. The example below will try to explain more fully.


 MUSHROOM BUSINESS 21


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