Research — Mushroom cultivation

In commercial mushroom cultivation it is general practice to provide a lower layer of compost which is covered by a layer of a material referred to as casing soil.  It is important in mushroom cultivation that the casing soil assists in maintaining a desirable moisture level for mushroom growth.  It should also maintain a desirable carbon dioxide and oxygen ratio.  Further the casing soil should maintain the nutrient balance of the compost and also act as a barrier to disease and insect pests.

To date, the only material which has been recognized by commercial mushroom growers as being acceptable for use as casing material is sphagnum peat.  Sphagnum peat is partially decomposed sphagnum moss and is obtained from Ireland, Holland and Canada (known as blonde peat). Sphagnum peat has the ability to retain moisture at levels suitable for plant growth, together with the required porosity and nutrient levels.

However, existing sphagnum peat supplies are becoming depleted. Thus, there is a need in the industry for an alternative to sphagnum peat.  Further more, the costs of obtaining imported sphagnum peat are high and add considerably to a commercial grower’s costs.  Thus, there is a further need for an economically viable alternative to sphagnum peat.

The difficulty with obtaining an alternative to sphagnum peat is that any alternative must satisfy the particular requirements for the cultivation of plants.  As mentioned above, a casing soil must have moisture-holding capacity to ensure that there is sufficient moisture to support plant growth.  Other important properties include neutral pH, low salt levels and suitable nutrient levels.  It has been observed that although other types of peat such as sedge peat are available they do not satisfy the above requirements and are unsuitable as casing soils.  To date, there has been no commercially available alternative to sphagnum peat.

In the horticultural industry, it is common practice to prepare artificial growth medium for use as potting mixes.  Such growth media must have desirable air porosity, water retention properties and sufficient nutrients to sustain plant growth.

Typical commercial potting mixes include a mixture of coarse sand and an organic material. Such a mixture on its own is generally deficient in many nutrients necessary for plant growth.  Thus, to provide a satisfactory mix, it is necessary to add the nutrients required for plant growth.

Typical organic materials are timber products such as bark chips and composted bark material.  Although these materials are generally obtained from by-products of timber production, their supply does rely on diminishing natural resources.

In an attempt to provide a plant growth medium with desirable properties a number of different combinations of materials have been researched.  Examples of these earlier studies include the use of filler materials such as bagasse, coconut fibre and rice husks with sphagnum peat moss and sphagnum peat.

Filler materials such as palm oil bunch / fibre are fibrous materials which contain no significant levels of nutrients.  Thus, it is necessary to add the nutrient rich sphagnum moss or peat.  However, as mentioned above, sphagnum peat is in finite supply.  Before now, it was believed there was no acceptable alternative to the use of sphagnum peat in the horticulture or mushroom industries.

It is therefore an object of the present invention to provide a growth medium for plants and mushrooms which may at least partially overcome the above disadvantages or provide the public with a useful choice.  It is also an object of the present invention to provide a material for use as a casing soil which may be used as an alternative to sphagnum peat and thereby creating a soil substitute.

Use of a growth medium for plants or mushrooms

A growth medium may be used in a wide range of applications including potting mixes, soil additive, mulch, mushroom casing soil and also as a top dressing material for germination of grass seeds.A growth medium for plants or mushrooms comprising of palm oil mill mud and non sphagnum-peat material selected from the group consisting of a non-sphagnum peat and coconut fibre can be provided.

The term “non-sphagnum peat” includes any peat material which is not derived from sphagnum moss.  Such peat materials include peat derived from sedges or trees.  Another suitable material is coconut fibre, which is known as coco peat.  Typically, coco peat consists of shredded coconut coir (the fibrous part of a coconut shell).  The coconut fibre may be either partially composted or used in its raw state.  Combinations of any two or more types of peat and/or coconut fibre may also be used.  Sphagnum peat may also be included as a minor component of the composition if desired.

The term “palm oil mill mud” refers to washing material from palm oil mills.  The washings include palm washings, lime, palm juice impurities and fine fibre.

Neither non sphagnum-peat materials or palm oil mill mud when used exclusively as a plant growth medium or casing soil is suitable for satisfactory plant or mushroom growth.  However, when a palm oil mill mud and non-sphagnum peat are used in combination, a material suitable for use as a plant growth medium or casing soil may be obtained. Neither product on its own is suitable for satisfactorily supporting plant or mushroom growth.

The ratio of non-sphagnum-peat material to palm oil mill mud is typically between about 1:4:1 to about 2:1 parts by weight.  Preferably the ratio is about 1:7:1.  The amount may vary depending upon the type of peat and source of the palm oil mill mud.  For example, the composition of the palm oil mill mud may vary, depending upon the source mill.

Typically, the respective amounts of palm oil mill mud and non-sphagnum-peat material component are selected to optimize desirable properties such as water retention, aeration, PH, salt content and nutrient level.  For example, non sphagnum-peat materials typically have undesirable properties such as low pH, low nutrient levels and low air porosity.  These properties may be offset by the palm oil mill mud which has near neutral pH, suitable nutrient levels and good air porosity. 

Conversely, undesirable properties of the palm oil mill mud such as high salt levels, low moisture retention, high levels or susceptibility to unwanted biological organisms are offset by the non-sphagnum-peat material which has low salt levels, good moisture retention and is substantially free of nematodes and other soil pathogens.