10
Comparison of commonly-used cycles: 5 weeks 2 flushes, or 6 weeks 3 flushes. Farm with 12 growing rooms. Yield in 2 flushes 28 kg/m2 and in 3 flushes 32 kg/m2. Compost filling rate of 88 kg/m2.
CULTIVATION Annual basis in 12 growing rooms of 330 square metres
Number of cycles Compost quantity Yield
5 weeks 2 flushes 124.8
3624 tons 1,153152 kg
Comparison 4.3 weeks 2 flushes, or 6 weeks 3 flushes. Same farm. Annual basis in 12 growing rooms of 330 square metres
Number of cycles Compost quantity Yield
three flushes). This gives slightly more flexibility in how the rooms are used, but the growth speed is identical.
Larger farms The comparison tables show that the dif- ference in yield between a five-week cycle with two flushes and a six- week cycle with three flushes is not spectacularly large. In my opinion, a two-flush system is only really advantageous if the cycle is shortened to 4.3 weeks (four weeks and two to three days) which means that the compost supplier has to fill on irregular days. In this way, the farm in the example achieved almost 30% higher production. So on larger farms the volumes can rise considerably using shorter cycles and two flushes. From a financial point of view, a lot rides on how much compost costs and the prices achieved by mushrooms. With a low compost price and high prices for mushrooms, switching to a two flush cycle is evidently worthwhile. The opposite situation may be reason to produce three flushes. Each grower must calculate these parame- ters for his own individual situation to disco- ver the most profitable way of production.
Diseases Now the theory has been dealt with, it’s over to the practical aspects. There is more to it than simply shortening or lengthening the cycle. There are plenty of growers, particu- larly in countries where compost is cheaper than in the Netherlands, who produce two flushes for completely different reasons. With a cropping cycle of just four and a half weeks the pressure of disease is far lower. An estimated 80% of all mould diseases such as dry bubble and cobweb disease only appear in the third flush. So skipping a third flush means eliminating a great risk of disease and growers can save time and money that would be used otherwise to con- trol disease. However, attention to hygiene remains a vital factor. The mushroom quality is often another motivation to produce two flushes. Third flush mushrooms are often not entirely up to scratch, and frequently have a shorter shelf life. Export-oriented countries like the Netherlands and Poland are therefore more likely to avoid the risk of
4. 3 weeks 2 flushes 146
4240 tons 1,349040 kg
having their produce rejected and stick to producing two flushes.
Activity So what is the secret behind a good third flush? There are multiple ways to produce a good flush, but the differences from farm to farm are greater for a third flush than, for example, the first flush. Some examples from practice. Sean Smith, grower at Fiddleford Mushrooms in England has the following to share about the third flush. “In the second flush I try to keep the compost at around 20 degrees by setting the air temperature to 18 or 18.5 degrees Celsius towards the end of the flush. Once the second flush has been picked, I set the air temperature to 21 degrees and apply 2 l/m2 of water. The CO2 is increased from 1600 to 2000 ppm and the RH lowered to 81-84%. The fan speed is also adjusted, from 38% in the second flush to 30% in the third. I leave the air temperature at 21 degrees until the compost tempera- ture has reached 23 degrees, that’s usually between 24 and 36 hours later. Then the air temperature goes back to 17.5 degrees, the CO2 from 1000 to 1400 ppm and the RH stays as it is. After a day or two, when the pinheads start appearing, the air tempera- ture is increased to 18 degrees to keep the compost at 19.5 degrees or thereabouts. Af- ter the second flush we usually stop picking for about four days and then three to four days in the third flush. In 2013, our average in our third flushes was 4.7 kg/m2. The qua- lity was good enough, with about 14% value pack quality. Of course, a third flush needs time and attention – we employ a full time production worker to control the diseases in the growing rooms for a weekly production of 42 tons of mushrooms. Our filling weight is 90 kg/m2.” Jos Hilkens from AdVisie says. “Towards the end of the second flush it’s important to encourage good activity by keeping the air temperature at a minimum of 18 degrees. The compost temperature should actually rise as the end of the second flush appro- aches, activity is crucial to a good third flush. If conditions become too dry in the third flush, you will get lots of poor quality pinheads. Too wet conditions, though, will
6 weeks 3 flushes 104
3020 tons 1,098240 kg
6 weeks 3 flushes 104
3020 tons 1,098240 kg
produce too few pinheads. The main points to watch are evaporation and moisture ma- nagement. I wouldn’t increase or decrease the air temperature during pinheading, but only maybe lower the temperature to 17 degrees once the pinheads are developing into proper mushrooms. Depending on the state of the casing soil after the second flush you could spray between four to eight litres of water. I would also make sure the fan is circulating enough, not less than during the second flush, and keep the RH at 88% to avoid losing too much moisture. Most com- posts are less active at the moment, so you have to encourage growth using air circu- lation. Make sure you keep on evaporating. In this way you should be able to harvest a third flush seven days after the second one.”
Discover your own solution All this goes to show that a conclusive ans- wer to whether a third flush is worthwhile is not easy. Each grower must examine his own particular situation and, central to providing an answer, calculate carefully. Providing cultivation is managed prudently and hygienically, modern farms should be able to produce a financially interesting third flush all year round. Another development is to approach the third flush differently to the previous flushes. There are growers in the Netherlands who harvest the third flush mechanically for the canning industry. This means a minimum of effort and a maximum yield in kilos. A third flush can produce an average of 7 kg/m2 in this way. Obviously, you have to have a contract in place with a buyer, and remember the price paid will be considerably lower than that for hand-pic- ked mushrooms for the fresh market. In the UK and Ireland there are also growers who thin the third flush and leave the remaining mushrooms to grow into flats – the large, open cap mushrooms for the fresh market. This is another way to producing extra kilos. But, the most difficult challenge of a third flush is keeping the flush disease-free. That means more work (labour) and preventive or curative measures, and higher costs. These factors are often overlooked when considering whether to produce a third flush or not. ◗
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