An interesting presentation was on yield modelling, a subject I have been fascinated by for many years. In this case, it was a talk by Professor Sharma on the possible use of the degree of reflectance / absorbance by compost using a range of different wavelengths in the Near Infra-Red range of  'light' (NIR), to forecast yield. Two of the final points made, were the relatively wide scatter of results, either side of the actual yield line and the fact that this line had a shallower upward slope than the theoretically perfect prediction line (which is at 45 degrees). Work is to continue for at least two years more and local compost makers have been asked to cooperate.  

The main problem with yield models is that different growing regimes appear to get best results from different types of compost. At one extreme, breakfast-flat growers who want to take just two flushes, do best with a relatively high moisture compost. At the other extreme, cup growers who want to maximise yield per ton and usually take at least 4 flushes, require a compost with relatively high dry matter. Another,
problem for the yield modeller is that growers tend to adapt methods to the compost they get most frequently. How do such observations affect the modeller? Firstly, if what is 'best' for one grower is not necessarily best for another, how is 'good' compost defined? Secondly, what should be best for a particular type of grower may not be so if it comes along unexpectedly. Thirdly, most growers have certain expectations, for example 500 lb per ton. Consequently, a 'poor' compost may yield better than it 'should' do in yield modelling terms because it is kept on for a
third flush when it really only warrants two. Furthermore, as there are likely to be relatively few mushrooms on it (bags or blocks), mushrooms are allowed to grow larger, thus making more efficient use of compost resources. On the other hand, potentially exceptional An interesting presentation was on yield modelling, a subject I have been fascinated by for many years. In this case, it was a talk by Professor Sharma on the possible use of the degree of reflectance / absorbance by compost using a range of different wavelengths in the Near Infra-Red range of  'light' (NIR), to forecast yield. Two of the final points made, were the relatively wide scatter of results, either side of the actual yield line and the fact that this line had a shallower upward slope than the theoretically perfect prediction line (which is at 45 degrees). Work is to continue for at least two years more and local compost makers have been asked to cooperate.

Composts tend to under yield on average because of serious over pinning in some cases. This results in poorer yields. Thus if some 'poor' composts over yield and some 'good' composts under yield, it is to be expected that a yield model prediction line (for growers in general) will be flatter than the 'perfect' line. If growers were able to assess a compost's potential before airing, this would help both average yields and ability to 'predict yield!'


An Interesting Farm Walk
As several of the above points occurred as discussion topics, this brings me to a most interesting farm walk. It was organised by Brendan Bums of Sylvan Spawn and took place on the 6 Nov at The Flush Mushroom Farm owned by Bernard Coey (brave man to have so many visitors tramping round and many thanks to him). The discussion leader was Dutch expert Hank van Gerwen. The farm was extremely clean, well organised, grows
A15, boasts a steamer for cooking out and in one house had stackable staging for blocks three tiers high. Needless to say, I found virtually no disease with very even, clean crops. I noticed only one bare section of bed, but apparently no spawn had been added to the compost, someone must have been on his tea-break!
Among the many topics were; -know your compost and adjust
accordingly. A bulky compost (tall bags and 'long straws') has a lot of potential energy and although it may be slow to start spawn run, particularly if it has low moisture, it is more difficult to crop successfully due to late heat surges, and may have a tendency to over-pin. However, it is potentially very high yielding if it also contains sufficient N. Short compost (straws well broken down) is easier to crop but has less potential. Exceptionally heavy, short bags may mean too high a water
content, thus are usually associated with low yield and/or poor quality. Difficulty in controlling spawn run temperature may be a good sign of high yielding compost. However, if temperatures rise above 30C, mycelium is 'burned'. Hank recommended aiming for 26C, others thought 24C maximum was best, as this gave more warning for cooling, particularly if a sudden heat surge occurs.

For high yields, casing should have plenty of small egg sized lumps and not be overly smooth. However, a 'smooth', even a rolled surface, may give cleaner mushrooms. Nevertheless rolling might be best restricted to compost suspected to be potentially low yielding. I suggest a flat surface should be avoided if high yields are likely, particularly with bags. Timing
of pressing the surface is also important. As late as possible is probably best.
Pinning methods were enthusiastically discussed. Brendan recommended an early break, but slow, with 'high' carbon dioxide and moisture at the start, gradually decreasing. However, accurate measurements are needed and sufficient experience required, as gained from keeping good crop
records. In my opinion this method gives time for pins to establish in 'depth' and with a range of dominance, then hopefully not too many will develop in the first flush and there will be plenty in reserve for the second. I believe extra third flush pins can form after the first flush, given the right conditions. High yields depend on obtaining three relatively
heavy flushes. Highest yields are obtained by taking a 4th flush, or by taking a proportion of breakfast flats. The heaviness of first flush pinning appears to depend on 5 factors, the energy in the compost, as discussed above, the structure of the casing the ratio of casing area to compost weight, the 'hardness' of the break and possibly most important, the amount of casing spawn and/or CACing. This was the third farm I had visited recently and on all of them I considered there was over heavy pinning. I considered this was probably due to use of too much casing spawn. Less rather than more than 'manufacturer's recommendation' is safest, as mushrooms appeared to be too close, although this was debated. This raised the two topics of discussion I found most interesting.

About 6 years ago, I remember drawing a graph for a poster in which I had plotted average mushroom weight against diameter. This graph had a sharp upward curve. It could be roughly summed-up by saying a 50% increase in diameter (not all that obvious) means a 100% increase in mushroom weight. Hank was very strong on this topic. He recommends a subtle picking regime to maximise yield. Pickers must be paid by the weight picked and it must be proved to them that if they are disciplined,
they can take home more money. They must only pick small buttons the first day (aiming to thin out and create space). On this day they will have low income. However they will then achieve maximum yield and earnings by going 'quickly' through the crop several times a day for the rest of the flush. They must only remove maximum size mushrooms (for the specified grade) each time. Such a regime requires very careful training plus supervision. Pickers must have some means of accurately gauging mushroom size, such as knowing the precise length of the picking knife blade to make comparison, size matters! I would like to add that the speed with which mushrooms expand depends on the compost temperature. Knowing this can be helpful in slowing things down, if there are insufficient pickers. Taking a bit more time can improve quality and may make all the difference regarding profitability. A further discussion point was maximum first flush weight. This can be higher on blocks because of greater casing area to compost weight. However, exceptionally heavy first flushes are usually detrimental to
yield because they usually 'dry out' the casing. Once casing has shrunk, it will not take up sufficient water to enable a good yield. Furthermore, if  'semi-dry' casing is watered during the flush, low quality, water soaked, stems may result.