Horticultural
Development
Company
Grower summary
M 49
Mushrooms: Effect of mixing
proportions of Phase II and
Phase III composts on cropping
Final Report 2009
© 2010 Agriculture and Horticulture Development Board
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© 2010 Agriculture and Horticulture Development Board
Headline
Blending Phase II (at least 67%) with Phase III appears to be most economically
attractive for growers currently growing mushrooms on Phase II compost spawn-run
in trays.
Background and expected deliverables
The use of Phase III compost allows growers significant efficiencies in the utilisation
of labour, energy and buildings compared with using Phase II compost, although the
compost cost is substantially higher. There is a shortage in the supply of Phase III
compost in the UK and significant amounts are now imported from the Netherlands
and Belgium where there is an over-capacity in compost production facilities. Due to
the high capital costs of building new Phase III tunnels, it is unlikely that the shortage
of spawn-run compost in the UK will be rectified in the near future. Work in the
Netherlands has indicated that a proportion of unspawned pasteurized (Phase II)
compost can be added to Phase III compost at the time of casing, with no adverse
effect on cropping. The unspawned Phase II compost becomes rapidly colonised by
mycelium from the Phase III compost (within three days of mixing), giving little
opportunity for the ingress of compost moulds. An experiment in Belgium showed
that the addition of 10% Phase II compost had no effect on mushroom yield
compared with 100% Phase III, but the addition of 20-40% Phase II reduced yield by
around 8%.
Objectives
The overall aim of this work was to increase the availability and reduce the
production costs of compost that can be cased at filling. The specific objectives of
this work were:
Objective 1 - Produce Phase II and Phase III composts in bulk tunnel facilities at
Warwick HRI.
Objective 2 - Obtain commercially produced Phase II and Phase III composts.
© 2008 Agriculture and Horticulture Development Board
Objective 3 - Determine the effect of adding different amounts of Phase II compost
to Phase III compost on mushroom yield, quality and crop timing.
Objective 4 - Assess the economics and commercial feasibility of mixing Phase II
and Phase III compost at filling.
Summary of the project and main conclusions
Two experiments were conducted in which mushroom cropping on different
proportions of Phase II and Phase III compost were compared with Phase III
compost alone. The proportion of Phase II compost ranged from 25 to 67%. All the
treatments were cased immediately after blending and/or filling into trays. The strain
A15 was used and no additional spawn was added during blending. The first
experiment was conducted with composts produced at Warwick HRI and second
experiment was conducted with commercial composts. Temperatures in the
composts were monitored. Three flushes of mushrooms were picked from six
replicate trays of each treatment.
Main conclusions
1.
In two separate experiments, adding 25 to 60% w/w Phase II to compost with
Phase III compost resulted in significantly higher compost temperatures after
casing than Phase III compost alone. The temperature surge following the
addition of 67% w/w Phase II was small and more delayed than that following
the addition of smaller quantities of Phase II to Phase III.
2.
Blending different proportions of Phase II compost (25-60%) with Phase III
compost produced at Warwick HRI had no effect on mushroom yield or crop
timing compared with the Phase III compost alone. However, blending Phase II
(33-67%) with Phase III using commercial composts delayed cropping by two
days and proportionately reduced yield compared with the Phase III compost
alone (up to 21.2% yield loss). This difference between the experiments may be
due to drier Phase III compost produced at Warwick HRI.
© 2008 Agriculture and Horticulture Development Board
3.
The mushroom yield losses resulting from diluting commercial Phase III with
25% or more of Phase II reported here and in previous work in Belgium would
outweigh any cost saving benefit compared with using Phase III alone. The
Belgian work indicates that at low inclusion rates of Phase II (15% or less), the
technique may be useful in smoothing out the supply of Phase III compost
during short periods of high demand, without the need for additional tunnels.
4.
The technique of blending Phase II (at least 67%) with Phase III appears to be
most economically attractive for growers currently growing mushrooms on
Phase II compost spawn-run in trays. There is no yield penalty compared with
using Phase II compost spawn-run trays, and there are potential cost savings in
buildings, energy, spawn and labour.
Financial and environmental benefits
Since there is no yield penalty compared with growing mushrooms on Phase II
compost spawn-run in trays, and no problems of compost temperature surge,
blending Phase II (at least 67%) with Phase III is more attractive to Phase II growers
than to those using Phase III.
Potential costs savings compared with Phase II spawn-run in trays are:

the energy, spawn-running room and labour cost of spawn-running compost in
trays before casing

spawn.
Additional costs are:

machinery and labour for uniformly mixing the Phase II and Phase III composts
before casing

the additional cost of either producing or buying in the 33% Phase III compost
over the 33% Phase II compost that is replaced.
It is possible that lower rates of Phase III than 33% could be used but this requires
further investigation.
© 2008 Agriculture and Horticulture Development Board
The results of this work indicate that the blending technique works well with drier
Phase III compost (63% moisture). This should be investigated further since delivery
of drier Phase III composts would reduce transport costs, and it could be used to
correct overly dry Phase III compost.
Action points for composters and growers

For composters and growers currently supplying or using Phase III compost, the
effects of adding small quantities of Phase II (10-15%) on mushroom cropping
and compost temperatures should be investigated.

For growers currently using Phase II compost spawn-run in trays, the technique
of blending Phase II (at least 67%) with Phase III before casing should be
investigated.

The potential for using drier Phase III composts (63% moisture) in the Phase II
blending technique should be examined. The potential for adding Phase II to
compensate for dry batches of Phase III should also be investigated.
© 2008 Agriculture and Horticulture Development Board