40
COMPOST
of raw materials. Once the compost has been loaded into the bunker and the doors closed, there is little left to be influenced.
Is a mixing line absolutely necessary for a good mixing process? Here the answer is ‘yes’, but there are other systems that if properly managed can almost equal the mixing quality of a good mixing line. As well as achieving a good mix and reducing the risk of error, a well-constructed mixing line offers the additional advantage of a high capacity per hour. In various parts of the world all kinds of methods are deployed to mix raw materials and while some of those systems work reasonably well, nothing beats a well put together mixing line. You do, however, have to be willing or able to take on this investment. The most important thing composters have to realise is just how vital good mixing is, and be aware of all the many aspects that combine to create a really good blend. I have seen some amazing results with the most low-tech mixing systems, but they are often incredibly time consuming with a very low output capacity. However, in less- developed countries a simple, low-tech mixing system can be the first step along the road to greater professionalism.
Are nitrogen values an indica- tor of nutrients in compost? Composting generally starts with a ‘cold start’, in other words a raw material formula to achieve the optimal ratio of raw material. An important guideline is the correct ni- trogen ratio. Many companies take samples regularly during the various phases of the process in order to monitor the nitrogen progression and to enable intervention if necessary. Remarkably, various nitrogen values are measured in different coun- tries even though production is good on both relatively low nitrogen values – as in the Netherlands- and on relatively high nitrogen values, as in the USA and Canada, for example. The different raw materi- als used greatly influence the amount of nitrogen present in the compost, and par- ticularly the amount of nitrogen available for the mushroom mycelium. In the USA, for example, typical American hay is used that cannot be compared with the hay available in North Europe. American hay has quite a high nitrogen content of 1.8 - 2.0 % and this type of hay clearly has a very positive im- pact on production. This type of nitrogen is readily absorbed by mushroom mycelium, as the mycelium develops very strongly and yields in the USA are clearly higher
Is a mixing line absolutely necessary for a good mixing process?
when American hay is used. Whether nitrogen from other raw materials (poultry manure) ultimately becomes an absorba- ble nutrient for the mycelium greatly de- pends on the entire composting process. If the process fails to proceed properly, very high nitrogen values are generally mea- sured that in due course will not result in high yields. Please note that high nitrogen values do not necessarily imply that the so- mething is wrong with the entire compos- ting process. High nitrogen values can have various causes. Supplementing the com- post also raises some questions. A number of years ago, a large mushroom producing chain in the USA presumed that depending on the nitrogen content in compost, it was possible to define which type and how much supplement could be used. But over time this did not appear to be as straight- forward and obvious in practice. As far as my clients go, practical experience shows that the better composted the compost is, the greater the effect of supplementing on mushroom production. Experience has also demonstrated that good management of
the compost temperature indicates the limit of how far you can go with supplementing and that the highest doses of supplement – providing the compost temperature can be controlled well – give the best results in terms of quality and quantity. This actually introduces an element of doubt concerning the assumption that poor compost res- ponds better to supplementing than a nitrogen-rich compost. The fact that phase II compost in the USA and phase III com- post in the Netherlands are supplemented as a matter of course says something about believing that ‘it doesn’t hurt to try’. Sup- plements contain readily available substan- ces like nitrogen in the form of protein, but are also rich in easily absorbable carbohy- drates. If mycelium develops abundantly in well-composted compost it seems that the mycelium can still absorb enough, readily available substances from the supplements. I personally view nitrogen values more as a guideline that indicates how much nutrition is present in the compost. In this sense, the nitrogen value could be seen as a barome- ter of productivity.◗
Does poor compost respond better to supplementing than a nitrogen-rich compost?
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