Poster Boy! - David Seaby in conversation about the posters at the 2001 conference!

It is going to take four articles at least  to do the All Ireland Mushroom Conference justice.

I was particularly interested in the posters and paper on casing, the latter was given by Liam Staunton and covered the work of his team at Kinsealy Research Centre.

In my article, italics give the poster or paper messages as I interpret them and non italics are mainly my opinions discussing the various themes that the posters or paper have introduced.

Is sugar beet lime needed any more?

Mairead Kilpatrick and her team have rocked the boat with the firm message that; Sugar beet lime, once the ingredient of choice for neutralising the pH of peat based casing does not necessarily improve yield or quality when it is mixed into casing based on heavy black peat. The same message is given by Liam Staunton and his team at Kinsealy.

Discussion

Originally when the change was made from using loam-based casing to peat-based casing the peat commonly used was ‘re-hydrated’ brown sphagnum peat. On the continent this is sometimes known as white peat. With this light fluffy material, Ralf Noble at the Horticultural Research Institute in England demonstrated that using sugar beet lime (SBL) at 10 or even 20% by weight as a pH neutralising agent in casing increased yield and particularly quality. However, at that time the SBL itself tended to be rather heavy, sticky and lumpy. Times have changed, most casing now mainly comprises black peat. This material might originally have been mainly brown sphagnum peat hundreds or even thousands of years ago. However, over time the tiny springy little leaves of the sphagnum moss plant have rotted and degraded to produce a peat that is more mud or like clay in consistency but nevertheless has a proportion of long fibres that may be the remains of old roots and stems of the moss or may be more recent fine roots that have grown down into the peat.

Tussock or cotton grass remains, also contribute to the fibre content of the casing.

The variability of SBL

Sugar beet lime was originally a precipitate of incredibly fine calcium carbonate particles that was created chemically in a vat of sugar solution; their purpose being to weigh down and drag beet debris to the bottom of the vat, to thus leave a purer solution of sugar. SBL is an interesting material because it has several properties that are different from those of ground limestone. It mainly comprises calcium carbonate particles that are much finer than any in ground limestone. If these particles were in the form of a dust, then a very small amount of SBL would be enough to neutralise the peat, due to the colossal surface area these particles provide. However, small particles have clay like properties and when SBL is wet it becomes sticky. SBL also has organic material in it derived from the sugar, the beet particles and eel worms and bacteria that have colonised it and then died. Young SBL has more organisms in it than old SBL. All SBL contains many minerals and trace elements, plus huge numbers of bacteria, most of which are probably beneficial to mushrooms. SBL can be lumpy, in which case its neutralising power is greatly reduced, or it can be a coarse powder, each grain of which is made up of large numbers of tiny particles.

The SBL ‘industry’ now supplies a fairly dry product. This is at the request of the casing manufacturers. They need to be able to mix this relatively expensive ingredient evenly into their wet black peat. Nevertheless, during a wet winter SBL can become damp and very lumpy. Trying to adequately mix wet SBL into wet black peat is not possible, unless the mix is churned. This is usually avoided with black peat for fear of destroying the peat’s delicate fibres and ending up with something like slurry.

These notes on peat and SBL are meant to illustrate why casing can be such a variable product; despite being made from what superficially appear to be just a few simple ingredients.

Some questions

Returning to the message of these two posters, i.e that SBL could be dropped because it no longer provides any benefits.

In defence of SBL, if it is in a powdery form, it can do an excellent job of pH neutralisation. It also contains a variety of trace elements beneficial to plant growth. These may or may not, in some circumstances, be beneficial to mushroom yield or quality. Usually SBL has very high populations of bacteria. It is known that certain bacteria stimulate pin formation. It is also known that certain bacteria out compete related disease bacteria. Does SBL contain bacteria that can reduce the chances of the blotch bacterium Pseudomonas tolaasi from thriving? According to the posters, there was no disease difference between SBL casing and ground limestone casing. However was the blotch bacterium actually present in the casings used? In the experiments, were warm, high humidity conditions encouraged, as only these would be likely to stimulate blotch developing? If the answer to either of these questions is no, then the case is not proved that SBL could be abandoned for the cheaper alternative. Although some growers never use SBL and claim to get excellent results, others say quality decreases and blotch increases when they don’t use SBL.

Sterilisation of SBL

In Mairead’s team’s second poster, experiments are concerned with SBL sterilisation. This work was stimulated by the small Salmonella outbreak, linked to Irish SBL, that had such a major effect on the mushroom industry and led to the code of practice for casing being developed. Experimental results indicate that heat treatment of SBL changes several of its measurable physical properties and one particular method of heat treatment effects yield. A second result is that percentage of SBL incorporated in casing could be reduced from 10% to5% w/w without reducing yield.

Discussion

This last result fits in with Mairead’s previous poster. However, the result that flame sterilisation of SBL reduced yields by 7% is possibly slightly at odds with this? The heat used in this ‘flame’ method is quoted as 75°C for 3 minutes. This is not nearly as severe as that quoted for the steam method, 121 °C for one hour. However it was only the flame method that reduced the SBL moisture content, albeit only slightly.

As part of the Conference, next day I had the privilege of touring Harte Casing where I was interested to see commercial flame sterilisation of SBL demonstrated. After this treatment, Hartes have had to return the SBL to its original moisture content by means of a water mist spray. To me, it is an intriguing mystery as to what could be the reason why SBL loses some of its ‘potency’ if it loses just 2% of its moisture content (this figure is from Mairead’s poster). Can SBL moisture and mushroom yield really be directly connected? Or is there an indirect connection such as bacteria re-colonising SBL after re-moistening?

Sterilisation of made up casing

A second part of Mairead’s poster, was concerned with heat treatment of made up casing; the aim being to kill any human gut pathogens, if it is conceivable that they are present. The heat treatment appears to be practical but requires further work.

Proposed work on casing

The second poster from Liam Staunton’s team at Kinsealy advertises proposed work on casing.

The point is made that blends of types of peat and types of lime to make casing for their various roles on bags/blocks/shelves are subjectively formulated (i. e. by trial and error). The team hope to use Near Infra Red spectroscopy to bring this possibly powerful tool to bear on casing formulation.

They also hope to look at heat treatments for casing and at the feasibility of recycling processed spent mushroom compost for use as casing; also screening various organisms that might be helpful in controlling pests and pathogens in casing is yet another topic for work.

Interesting tour round Harte Casing

As mentioned there was a most interesting tour round the Harte Casing complex. Besides seeing evidence of their peat harvesting machinery business and their massive proposed horticultural peat venture, we saw a computer controlled casing production line that blends three types of peat and two types of lime to produce an astonishing 60 different casing formulations. This would appear to contrast with the philosophy of my correspondent Mr Brian McGregor in Scotland, who says his simple solution is to mix one standard uniform casing and tell the growers to get on with it!

Watering casing

For all the growers who spent most of the day in the trade show, you missed a very interesting paper delivered by Liam Staunton on his team’s work entitled: ‘A study on casing management by Irish growers.’

The methods of twelve Irish growers using different systems were studied over an extended period of time.

To understand the results, two terms must be explained.

If a casing is saturated with water to such an extent it could hold no more, it is at its water holding capacity (WHC)

At any stage in bringing the casing up to this, the water (or moisture) content (WC) of the casing could be determined. This is just the percentage weight of the casing that comprises water at that moment in time.

Different casings arrived with the grower having moderate differences in WHC, the range being 81.5% to 86.5%. However, the actual water content on arrival (WC) had a much bigger range 62.9% to 85.5%. Thus while some casings were at their WHC on arrival, others were very far from it. The most interesting point is that the growers did not accurately recognise the amount of water that should be applied to bring their casing up to near its WHC and furthermore the growers often did not know how much water they had put on anyway, because they did not have a water meter. Knowing the WHC of the casing on arrival and measuring the WC of the casing at several key stages, illustrated that during case-run, on average about four times as much water is applied as can be accounted for in raising the WC of the casing. Where does all this water go to? Some will miss the bags or blocks and end up in the alleys. Much of it will evaporate and this may vary with fan speed. Some goes through the casing and into the compost and some collects at the bottom of the bags. Liam suggested that water saturating the compost would cause it to rot and become unavailable for the mushroom mycelium. This could cause a big loss in yield.

On the other hand I met a ‘good’ grower who wanted to get moisture through the casing and into his phase III compost because he thought it would help his yield!

Casing with substantial mycelium in it is quite water repellent,

Another interesting fact that emerges, from a table of results provided, is that despite four times as much water being applied as is theoretically needed to bring casing to its WHC, at the end of case run, the casing has only 2.4% more WC than when it arrived.

Questions, questions, questions.

Obviously, more work needs to be done to answer the following questions.

1. Does water running into the compost from the casing increase or decrease yield?

2. If excess water decreases yield how best to avoid this water incursion?

3. How do growers judge how wet a casing is on arrival and is it possible to use a water meter to judge when to stop watering, particularly when such a high proportion of applied water seems to go missing?