Mushroom Culture

Cultivation Technique (Contd..)

C. CASING
What is casing?
Covering the top of mushroom beds after completion of spawn run with a layer of appropriate soil mixture is known as casing. Mushroom growers in different countries use different types of casing materials depending upon their availability . Different materials used in India as casing mixture are:

1) Loam soil + Sand ( 4:1)
2) Two year old farm yard manure + loam soil (1:1)
3) Two year old spent compost + sand + lime (4:1:1)
4) Two year old spent compost + loam soil + FYM (2:1:1)
5) Paper mulch + 2 year old spent compost
6) Two- three year old spent compost + FYM (1:1)

Why Casing is necessary?
Casing of mushroom beds or spawn run compost is necessary because:

• Casing soil is a nutrient deficient medium, which helps in converting the vegetative phase into fruiting.
• Fruit bodies are formed in abundance and thus production is economical.
• It helps in conserving the environment in mushroom beds

Characteristics of a good casing :

• Good water holding capacity and more pore space percentage.
• Capable to release harmful gases during cropping.
• Free from harmful microorganisms.
• pH should be slightly alkaline.
• Should be properly decomposed.
• Free from heavy metals and ions.

Treatment of casing soil:

For killing various pests and disease propagules present in casing mixture, casing soil is treated with chemicals or pasteurized with steam.

1. Chemical treatment of casing mixture :

• Casing can be disinfected with formaldehyde treatment.The formaldehyde solution is prepared by mixing 2 litre of formalin (4O% a .i) in 40 litres of water to obtain 2% solution . Casing mixture, made up into a rectangular pile, is drenched thoroughly with this solution and then covered with a polythene sheet or tarpaulin sheet. The treatment should be given at least 2 week before casing is to be done. In other words, casing should be prepared and treated immediately after compost has been spawned. It should be ensured that casing mixture should not have traces of formalin when applied on the beds.

2. Pasteurization of casing mixture:

• In farms where facilities for pasteurization of compost with steam are available, casing can also be pasteurized. For pasteurization of casing mixture, casing soil is filled in trays and trays in turn are stacked in the pasteurization room. Steam is introduced to bring the temperature of casing mixture to 65-70°C and which is maintained for 6-8 hours. All the harmful microorganisms, including mushroom nematodes are killed at this temperature. Useful bacteria like Pseudomonas which play a positive role in introduction of fruit bodies are not killed and survive at this temperature for 7-8 hours. Casing soil pasteurized in this manner gives best result.

Fig. 6.5 Heap of loam soil used as one of the casing ingredients

CASING APPLICATION AND MYCELIAL COLONIZATION :

Fig. 6.6 to 6.9 Mycelium threads from grain spawn spreading in the compost filled in polythene bags.

Application of Casing:

• When spawn run is completed, the casing is done over spawn run compost after removing newspaper sheet from the trays on racks or after opening mouth of the poly bags. Spawn run compost is slightly pressed and covered on the surface with 4-5cm thick layer of casing soil. After casing, the temperature of the mushroom house is maintained at 24-25 °C for another 8- 10 days and water is sprayed over casing soil. Within 8-10 days,white mycelium spreads in the casing soil. Thereafter temperature of the mushroom house is lowered down to 18 °C and maintained between 14-18°C during rest of the fruiting period. Whenever required ,watering is done with the help of sprayer and RH is maintained at 80-85% throughout the cropping period.

D) CROP MANAGEMENT:

• The casing medium harbours some beneficial bacteria and activated charcoal like material which help in initiation of fruiting bodies on the casing surface. Casing mixture also helps in conserving moisture in the beds and gives support to the fruiting bodies .
• As soon as the white cottony growth of the mycelium appears on the casing surface, fresh air should be introduced inside the cropping room and bed temperature lowered to 16-18 °C which is to be maintained throughout the cropping period . The CO₂ level is also lowered to below 1000 ppm. Under such conditions, the initiation of fruiting bodies i.e.pinning takes place within 6-7 days of aeration which reaches to the harvesting stage within next 4-5 days. The individual fruit bodies are harvested carefully without disturbing the adjoining pinnings and before the cap opens. The cropping period lasts for 40-60 days. Mushrooms appear in flushes provided optimum conditions like bed temperature ( 16-18º C) , relative humidity (80-90 %) by spraying water with misty nozzle, about 4-5 air changes every hour resulting into less than 1000 ppm in the cropping room with no light at all , are maintained.
• The environmental factors like temperature, relative humidity, light , air flow in the cropping room etc; all play vital roles which together determine the nature of further mushroom development. The mushroom crop grows in cycle called “Flushes” or " Breaks ". Depending on the species being grown, day intervals with each successive flush bearing fewer mushrooms. These flushes normally appear in 7-10 days.

Fig. 6.10 & 6.11 Button mushroom beds in cropping stage
Fig. 6.12 & 6.13 Photograph of a Hygrometer for measuring humidity (a) and water being sprayed on the cropping
beds with the help of a foot sprayer pump having a fine spray nozzle (b)


Fig. 6.14 & 6.15 Showing the compost bags kept on shelves for spawn run, the air duct and the Air Handling Unit in the cropping room (a)
the ventilator for entry of fresh air and the controlling board fitted outside a cropping room (b)

E) HARVESTING:

• Timing is the most important factor in button mushroom harvesting. Mushrooms should be picked before the veil breaks and the stem elongates. Damage to pinheads and disturbance of the casing soil must be minimized during picking. The standard harvesting technique consists of grasping the base of the stem, pull it with a twisting motion being careful not to disturb adjacent pinheads. The stem base, with mycelia and casing particles adhered to it, is trimmed with the help of a short bladed knife. All trimmings should be kept in a plastic bag and removed from the cropping area. Mushrooms growing in clusters should be broken apart and harvested individually. Immature mushrooms should be left attached to the casing for further development.

Fig. 6.16 - 6.18 Harvesting of mushrooms with the help of two fingers and a thumb and cutting of stem root with a knife

F) Yield :

• The cropping stage lasts for 40-60 days and production comes to 12-25 Kg / 100 Kg compost depending upon the quality of spawn, compost, casing mixture and prevailing environmental conditions in the mushroom house.