Some growers don't realise the vital  difference between gross and net income. The latter is what is left after paying all the bills including interest on loans. Suppose a growers spends GBP100,000 on a state of the art shelf system. The funding body will probably want at least GBP15,000 a year in interest plus repayment. Gross income will have to increase by much more than this to justify the risk. For example if equipment lies idle it will still cost GBP15,000 p.a.

If Phase III compost is required for maximum efficiency, this may not be available. Even if it is, it is prone to contamination by a weed-mould Penicillium that greatly reduces yields and also mushroom quality, not to mention producing hazardous spore dust at emptying. Granted that Phase III is both highly productive and increases throughput by virtually eliminating spawn-run time. So if Phase III is not available and the grower is forced to rely on Phase II, net income may be less than it was prior to making the investment.

Some growers enhance their gross income by buying an abundance of compost. They skimp on spawn run time and only take two flushes, thus increasing the number of crops per house per year.

However, growers who buy say two thirdsthis amount of compost but fully utilise it by taking three, four or even
very occasionally five flushes, end up with higher net incomes per house. The main problems with multiple flushes are disease prevention and keeping pickers happy. In my opinion the nine week cycle has a lot to answer for in decreasing net incomes even though it may often increase gross income. Its
main recommendation is that it satisfies pickers and possibly compost makers. A principle disadvantage is that it encourages skimping on spawn-run time.

 Growers sometimes regard Agaricus bisporus as being 'man-made', however its physiology is essentially that of a field mushroom that feeds on soil organic matter at temperatures that rarely reach 20C, let alone 30C. Spawned compost stored in the fridge still 'runs' at 10C. As I have written several times, a spawn-run at 19C is much preferable and more productive than one that peaks at 30C or more. As soon as 24C is exceeded, mushroom mycelium runs less well and some competing fungi thrive.

For example at 30C Trichoderma grows several times faster than Agaricus. Furthermore, compost is packed with heat loving (thermophilic) fungi that protect it from weed-moulds at 19C but above 24C begin their own agenda of rapidly burning up compost resources.

When ordering compost, particularly in the summer, make sure you are fully ready to receive it. If it has to sit on a pallet for more than a few hours it is likely to heat up. This will kill some of the spawn and also stimulate thermophiles into a spurt of growth that can be extremely rapid.

I remember making an Indonesian food called Tempeh. Cooked soya beans were inoculated with spores of a thermophile called Rhizopusoligosporus, within 16 hours at 30-40C the beans had been partially digested and so tightly woven together they resembled brie cheese. During the summer, assess ability to control temperatures. Only fully fill houses that have efficient cooling and dehumidification systems. From a net income point of view it is better to fully utilise a half filled house than half utilise a fully filled one!



Know your compost, this is bound to vary in productivity over time. It is affected by weather conditions during production, straw quality, formulation problems and a variety of interacting factors. Studying compost utilisation efficiency I have become convinced that bunker-compost is generally more productive than wind-row compost. Bunker-compost contains a higher proportion of straw to poultry litter. This means more cellulose, that is easily digested by Agaricus and less lignin that is poorly digested. Nevertheless poultry litter is a vital ingredient, not only providing nitrogen and minerals but also thermophilic bacteria that initiate the composting process.

 In a bunker, higher temperatures result in more ammonia being chemically bound to the straw than in wind-rows where much is lost to the atmosphere. Less nitrogen lost, less poultry litter is needed.

Different composts require different treatments. A high moisture compost needs a drier casing otherwise mushroom quality suffers. It may need some heat whereas a high dry matter compost may be slow to run but for an entirely different reason.

The spawn has difficulty at first obtaining the moisture it needs. It certainly does not require heat and will give only high yields, provided it is given sufficient time to spawn run. It will benefit by having a very humid house during spawn-run. If it is cased too early high case-run temperatures will tend to cause the casing to be flooded by mycelium. This will make for too many pins and difficulty in re-wetting the casing at watering. A bulky compost may have similar problems to a dry one, as it is also likely to contain more heat producing energy. Compressing it more strongly at levelling aids an early start to spawn-run.

 Mushroom quality largely depends on getting the mushroom's dry matter correct; at 6% mushrooms are pink and easily bruised. A dry matter around 7.5-8% is good. Above this, mushrooms become very firm and yields are reduced. Mushrooms take a proportion of their moisture content from the casing. If water is too freely available they will have a low dry matter. Mushrooms expand much more rapidly at high temperatures, thus giving less time to lose water by evaporation. The worst case scenario for poor quality is high temperatures, high humidity, high moisture compost and wet casing.

Yields are found to be increased if casing is dense enough to retain CO2 during the first half of case-run. It is often better to somewhat compress the casing than to over-water to achieve this. The upper half should then be ruffled on say day five.

In a no ruffling system where mycelium is 'knocked back' if need be simply by watering, mushrooms often have too much moisture available in the first flush, leading to poor quality with possibly too little later, leading to poor yield!

By David Seaby