T i p s
A publication in support of mushroom growers
(printed with permission)
By Danny Lee Rynker*
(Author´s pictures)
Danny Lee Rynker
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* About the author:

Danny Lee Rinker
Department of Plant Agriculture
University of Guelph, 4890 Victoria Avenue, PO Box 7000
Vineland Station, ON L0R 2E0 CANADA

Many species of mushrooms are cultivated world-wide. Global production increased to about 6.2 million tonnes in 1997, with a more than 12% increase annually from 1981 to 1997 (Chang 1999). Seventy percent of the global mushroom production is derived from three mushroom groups, Agaricus bisporus, Pleurotus spp, and Lentinula edades. The remaining mushroom volume is
generated by at least a dozen species (Chang 1999).

In the production of any and all species, signifícant residual material remains after cultivation. Every tonne of mushrooms produced results in one to two tonnes ofdry spent residual material. The important question in this day of limited natural resources and concems over human health and the environment is, "What use or value does this residual material from mushroom production have?"

The following discussion briefly outlines the materials and techniques used to produce the vast volumes of "spent" (used) mushroom substrate in the production of these principal mushroom species.
Oyster mushroom (Pleurotus spp.) spent compost.
Winter landscape of Vineland

Spent substrate from
Agaricus bisporus production is already in wide use as follows: 

In horticulture as a component of potting soil mixes.

In agriculture or landscape trades to enrich soil.

As a casing material in the
cultivation of subsequent Agaricus crops.

In vermiculture as a growing medium.

In wetlands for remediation of contaminated water.

In stabilizing severely disturbed soils.

In the bio-remediation of contaminated soils.

As a bedding for animals.

As an animal feed.

And to control plant diseases.
Many species of mushrooms are cultivated world-wide. Global production is greater than six million tonnes and has an approximate value of at least $US 14 billion. Mushrooms are produced on natural materials taken from agriculture, woodlands, animal husbandry, and manufacturing industries. After mushroom crops are harvested, millions of tonnes of "spent" (used) mushroom substrate become available for other uses. The used growing medium is far from spent. Many beneficial uses for spent mushroom substrate are currently being implemented or evaluated intemationally. These uses vary with the mushroom species. Most of the published literature in the
West describes the use of spent mushroom substrate from the cultivatíon of the Agaricus bisporus species (although less than 40% of the spent material is from this species).
Spanish version
The commercial mushroom, Agaricus bisporus, represented about 32% of the worid mushroom productíon in 1997 (Chang 1999). This species is cultivated typically on a straw or hay base,
amended with animal manures and gypsum.  The materials initially undergo a two-phase composting process, one at high temperature (up to 85°C) and another for pasteurization and
conditioning (beginning at 60°C and decreasing to about 45°C). The colonization stage by this mushroom fungus is followed by covering the surface ofthe colonized compost with a layer of peat, top soil or other suitable material. Within two weeks mushrooms are visibly ready for harvest.
After about three weeks of mushroom harvest, the growing material is considered spent. After usually undergoing a post-crop heat treatment, the growing material is removed and the chamber is ready for a new crop.
The oyster mushroom consists of a number of several edible Pleurotus species. This species represented 14% of the worid productíon in 1997 (Chang 1999). Pleurotus can be cultivated on wood sawdust, on various plant fibres or plant residues, which are amended with locally available proteins and carbohydrates to optimize its growth requirements. The materials are generally not composted previous to inoculation. The wood sawdust may be aged or the plant fibres hydrated for
several days. The growing materials are treated with either heat or chemicals to augment the selectivity of these materials for the oyster mushroom fungus. After colonization is complete, the
colonized substrate is subjected to conditions suitable to initiation and maturation of fruiting bodies.
At the end of several mushroom harvests, the growing material is considered spent. It may be heat treated before being removed from the growing chamber.
Shiitake mushrooms, Lentinula edades, represented 25% ofthe 1997 worid mushroom production (Chang 1999). This species is either cultivated on natural logs or on a 'synthetic' logs. Natural log production utilizes various species of trees, especially oak. Trees are cut down after leaf fall and the wood cut in lengths of about one meter. Within one month these logs may be inoculated with the shiitake fungus. After up to one year of incubation, the colonized logs are brought under conditions that initiate fructifícation. Mushrooms are harvested about twice per year for several years. Once production ceases, these logs are considered spent. 'Synthetic' logs for production of shiitake mushrooms are formed from sawdust, straw, com cobs or mixtures thereof. Starch-based additives from cereals are often added to optimize the nutritional needs of the fungus. The growing materials are generally sterilized. After colonization is completed, conditions are changed to initiate the formatíon of mushrooms. After several harvests, these synthetic logs are considered spent.
This paper will outline the utility of spent mushroom substrate. Characteristics of spent substrate are outlined, and the following uses for spent substrate are detailed: Bioremediation, crop production, re-use in the cultivation of mushrooms, food for animals and fish, and pest management. Each of these uses is noted in association with one of the particular mushroom species noted above. The environmental impact of weathering spent compost is also discussed.
Agaricus bisporus
Pleurotus spp.
Lentinula Edodes
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Spent substrate from
other mushroom species has found acceptance: 

As food for animals.

As ingredients in
the cultivation of other mushroom species.

As fuel.

As a medium for vermiculture.

To enrich soils.

And as a matrix for bio-remediation.
This paper will describe the utility of spent mushroom soil as well as point to potential additional uses for this valuable substance.