Photo 2: Round, hollow tubes give double the volume of fl attened straw.
Photo 3: 10% structure straw gives clearly more volume.
Interestingly, (see photo 3) if 10 flat straw tubes are replaced by 10 round ones, the volume jumps to 7.5 cm.
This fact translates into practice as follows: if you have to work with poor quality horse manure at the composting plant, you can still create enough structure in the finished compost by adding 10% of good quality straw to the blend. The water content does not need to be reduced as drastically, so a more optimal moisture content will be preserved for the fermentation process and mycelium growth. With poor quality straw, applying a slightly drier fermentation process will result in a number of less fermented pieces of straw that will ensure sufficient volume. 10% of straw added for structure may not provide a great deal of nutrients, but it will make sure that enough nutrients can be absorbed from the remaining 90%!
Retaining structure Good structure starts with good raw materials. You can try to retain structure, but creating more structure during fermentation is impossible. If the raw material has too much structure, adapting the processes at the composting plant can solve this. Real problems only start to appear when the raw material lacks struc- ture, a situation often caused by a poor straw harvest that particular year. Less structure is not necessarily equal to a shorter fermentation time. Fermenting is necessary to homogenise the blend, make it selective, release nutrients and bind ammonia, and by definition this process always adversely affects the structure. A frequently recurring mistake is shortening the fermentation process in order to preserve structure. Practical experience shows that this
usually leads to poorer production results at the farm as not enough nutrients are available for the mushrooms. During fermentation, extra mixing, lower temperatures, ammonium sulphate and wetter compost all cause the structure to deteriorate. Composters can take action and try to end up with more structure. There are also factors that impact negatively on structure during pasteuri- sation and mycelium growth. Prolonged level- ling, a premature release of ammonia, too many actinomycetes, type and speed of the pulling winch and too high filling weights all play a part in causing additional structure loss.
The importance of structure The temperature and supply of oxygen in bunkers and tunnels are regulated by blowing incoming air into the lower layer of compost. The more compacted the compost is, the more difficult it is for the fan to supply enough air. In bunkers this can result in an anaerobic process, and in tunnels in excessively high temperatures. Using more powerful fans gives more options, but this too has its limitations. When filling tunnels the m3 weight of the compost should taken into account and the moisture content and filling height adapted to suit this weight. If you fill just a little too much compost there will be immediate consequences (see photo 4). Precisely the same compost was then filled into two different tunnels. Tunnel 16 was filled with 5% more compost than tunnel 14. During conditioning this means that the temperature of the air through the compost has to be lowered from 44.5 degrees Celsius to 42.5, but even so the compost temperature rose from 50 to 53 degrees – which inevitably slows the
Moisture percentage and
filling weight are proportionate to structure.
MUSHROOM BUSINESS 15
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