means the grains do not swell and too many nutrients are left in the stalks and leaves. This can also cause acidification, no matter how dry the straw is.


Other raw materials (American hay) are usually well weathered. This inhibits acidification to a great extent, but the hay is compact and therefore more sensitive to anaerobic patches if the hay is not pulled apart properly during pre-wet. Corn cob pulp is also susceptible to an oxygen deficiency during per-wet. Frequently turning the pile during the pre-wet period is crucial.


The importance of oxygen measurement


Not all forms of pre-wet are equally effective. There is often no oxygen measurement and aeration, even at this early stage of the process. For example, if straw bales are immersed in water containing slurry, and the wet bales are then ‘set aside‘ for one or more days, the space left between them makes a huge difference. Using portable oxygen sensors, I have seen some oxygen measurements that can be surprisingly low, ranging from 0% to 9% at that moment of the process, depending on the availability of natural aeration and therefore the oxygen supply. Even placing a pallet underneath the bales can make a difference. At more professio- nal and automated plants, the straw is mixed with other raw materials and then placed on an aerated floor to guarantee a good flow of oxygen. But they sometimes do not measure the oxygen concentration then. Even at pre-wet, monitoring


Without proper oxygen


measurement at every stage of the process, many negative influences go unnoticed.


the process using permanent oxygen measure- ment so the level of aeration can be optimally adjusted to suit each temperature zone it is very important. Some say that an oxygen sensor only measures the oxygen at a single point. However, those with good experience of oxygen measure- ment have far better insight of how the oxygen reacts in the straw during pre-wet and later on. I am sometimes told that no more traces are to be seen or smelt of the anaerobic patches that occurred earlier in the process. But appearances are deceiving, as acidification at any moment can be damaging for production! If there are many other problems at the plant, influences like this will go unseen. As mentioned earlier, the fact that straw is already acidified in the bale is often unnoticed, as the straw feels dry. But acidification could have been caused if the straw was baled under sub- optimal conditi- ons. It is very important to ascertain this immediately, which demands permanent monitoring and – after the bales have been opened and wet – treated to plenty of oxygen. This approach also has its limitations, namely in the duration of the treatment and the speed at which air is blown through. The downside could be excess removal of moisture. One signal that indicates acidic straw is an intense, white colour. There is a big difference between free water and absorbed, locked in moisture. Too much water visible between the straw blades greatly limits optimal aeration. Plus, there will often be considerable differences in moisture concentra- tions in straw and compost if the moisture has not been absorbed properly by the straw. When a nitrogen source such as chicken manure is added to a carbon-based product such as straw, increasing activity will start, certainly if there is a good water-oxygen balance. The compost structure plays an important role here. The microorganisms will consume a large part of the oxygen, principally just after the manure has been added. Good oxygen measurement is essential at this stage, as without it, the optimal aeration levels are not provided. This was proven


oxygen values. MUSHROOM BUSINESS 9


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