Paul Baxter, Queen's University Belfast and AFBI, Loughgall describes the results of research that will provide a rapid analysis tool for mushroom casing to enable suppliers and growers to maximise casing potential.
The work is funded by Teagasc and the Department of Agriculture & Food, STIMULUS fund.
One of the biggest challenges casing suppliers face is to provide a consistently high quality product that meets the individual specifications and expectations of growers. However, the inherent variability of peat creates numerous problems. Variation will exist between and within sites, seasons and depths of extraction from the bog. Suppliers are therefore continuously altering casing blends in response to the properties of the raw peat and they must further tailor these blends to the specific needs of individual compost and cropping systems i.e. Phase III, blocks or shelves.
No two casings are the same; each will have properties - physical, chemical or microbial, that to a greater or lesser degree are different. Suppliers generally have two or more distinct peat types that can be blended to create a particular casing 'recipe'. Ideally, the properties of each peat will complement those with which it is blended to create an optimal casing. So how are the correct blends assessed?
At present, although results from standard analysis can help formulate casing, the final blend is usually based on the subjective experience of the person mixing it. Many of the important physical properties are readily analysed with standard laboratory skills and equipment but the main obstacle for suppliers, is the time taken to do this. pH and electrical conductivity (Ec) results can be easily obtained in under 2 hours, but water absorbency and retention analysis take up to 5 days, aeration even longer. Such timescales are impractical in commercial practice.
Ideally, every casing batch would be rapidly analysed for a range of properties and results provided to the grower within 24 hours. These would then be used to assess the most appropriate casing watering and management strategies. In addition, the supplier would have immediate feedback and could adjust blending ratios of the raw ingredients to ensure consistently high-quality product.
Research currently being conducted by Queens University at AFBI, Loughgall is assessing the potential for such a rapid analytical system. Over the last two years peat and casing samples have been collected from various suppliers and peat bogs around Ireland.
Using Near Infra-red spectroscopy (NIRS) the samples are scanned in a couple of minutes and a spectral graph produced (Fig 1). Alone, a spectral graph means nothing - it has to be calibrated against physical data...and lots of it!
Spectral graph of a casing sample
To date, over 140 samples of fresh peat and casing have been scanned and analysed for over 30 physical and chemical parameters. The data is then statistically analysed against the corresponding spectral graph to produce a correlation relationship.
The higher the correlation (i.e. closer to 1) the greater the accuracy between predicted values (spectral data) and actual values (analytical data) (Fig 2) and the greater the potential for NIRS to rapidly determine various essential attributes in casing samples.
Physical & Chemical Analysis Data
Graph showing the relationship between predicted and actual values - the closer to the line, the more accurate the correlation
So far, the ability of NIRS to rapidly analyse casing and raw peat samples has shown high correlation with important parameters including water retention, water absorption, pH, ash content, dry matter, calcium and manganese levels.
To complement the NIRS work, all peat and casing samples were also analysed by thermogravimetry (TG), a technique that shows various fibre fractions and by-products of decomposition.
TG works by heating samples over a temperature range at predetermined increments. As the sample heats up, chemical compounds combust (burn) at specific temperatures with a resulting loss in mass. The more stable a compound, the higher the combustion temperature required.
By subsequent analysis of thermograms (Fig 3) the degree of peat humification (essentially the 'age' of the peat) can be determined.
Increasing temperature with time
Casing analysed with TG - the thermogram illustrates the rate at which mass loss (combustion) occurs at different temperatures. The overall decrease in sample weight can be seen also in the weight loss curve.
This in turn, will provide further information on the likely water retention, absorption and aeration properties of the various peat types thus enabling more appropriate selection for blending.
The importance of casing in mushroom production must not be underestimated. This is particularly relevant as cropping patterns change to a smaller number, of heavier, extended flushes with the altered water demands these put on casing.
This research can help by providing accurate rapid analytical techniques that offer improved characterisation of both peat and casing blends thus maximising casing potential.
Note: Original graphs can be provided on request. Email firstname.lastname@example.org