Some Thoughts on CO₂ Control in Mushroom Culture

by Lee C. Schisler

Many researchers have done extensive experiments with the effects of CO₂ (carbon dioxide) on mush?room growth. The following generalities and remarks will be based on their research and some practical ex?periences of my own.

CO₂ levels should be maintained at between 5000 or 15,000 ppm during spawn growing, or that portion of the production cycle between casing and the ap?pearance of mushroom mycelium on the casing layer. The time normally required for spawn to reach the surface of the casing is from 6 to 10 days, depending on the material used for casing, depth of the casing layer, moisture content, and temperature in the mushroom house. The house or room is then flushed with fresh air, reducing the CO₂ level.

White strains generally require 1000 ppm CO₂ or less, whereas light cream strains will fruit at 1500 ppm CO₂ or less. As I have had little experience with off-white and old-fashioned brown strains, I cannot give you good figures for these. Spawnmakers sup?plying these strains generally have this information. This level of CO₂ should be held constant until the mushrooms enter the rapid stage of enlargement (when caps reach 0.5 to 0.75 inch in diameter). The CO₂ should then be raised an additional 500 ppm to enhance enlargement of the mushrooms. For most white strains this would be adjusting to 1500 ppm and maintaining that level until the end of the crop; for light cream, it would be 2000 ppm.

After having said all of this, let me qualify it by stating that these levels of CO₂, especially those given for after casing, are for a point 2 inches above the casing layer in a forced-air ventilation system with good air distribution. It is important to add that the stated levels will vary according to the peculiar cultural properties you provide to the crop.

In summary, CO₂ levels can be controlled in mush?room houses by regulating ventilation. Ventilation procedures will vary from farm to farm. In general, however, regulation of ventilation should provide for higher CO₂ levels (5000-15,000 ppm) during spawn growth and immediately after casing. A sharp in?crease in fresh air introduction should follow (thereby reducing the CO₂ level) to allow for optimum pin?ning. The proper CO₂ level at this point will vary ac?cording to the strain of mushroom being grown. After mushrooms begin to enter their rapid stage of enlargement, fresh air ventilation can be slightly re?duced, allowing an approximate 500-ppm increase in CO₂ levels, which should assist in "sizing" mush?rooms and facilitate picking. This CO₂ level should be maintained throughout the remainder of the pick?ing period.

"New" Innovations For Efficient Mushroom Growing

by Lee C. Schisler

I have been asked from time to time to rate commer?cial mushroom growing, based on present-day knowledge, in terms of biological efficiency. In other words, how many pounds of mushrooms per pound dry weight of compost should a commercial farm ex?pect to produce in a 35-day pick with the knowledge and innovations available to us today? My ratings in terms of lb yield per lb dry weight of compost are as follows:

0.3 to 0.5 lb yield/lb dry compost = poor 0.5 to 0.7 lb yield/lb dry compost = average 0.7 to 0.9 lb yield/lb dry compost = good 1.0 or more lb yield/lb dry compost = excellent

Whether or not you agree with my ratings or whether this criterion is even valid for evaluation of a mush?room farm is a matter of opinion. However, regard?less of opinions, let me ask the following two ques?tions: 'How does your farm rank in the above ratings?' and 'What new innovations - if any -should you adopt to achieve a desired rank?' These are questions only you, the grower, can answer.

To begin, may I suggest at least a few ways to reach a high rating, primarily by taking a new look at "old" methods.

1) Composting. Follow the short composting method of compost preparation:

a) Phase I. Use proper raw materials and supple?mentation schedules so as to achieve a nitrogen level of 1.5 percent prior to the initiation of com?posting. Proper composting temperatures should be obtained in the compost piles (160? to 175?F). There should be no leaching from the piles at any time, thus eliminating anaerobic areas in the pile. Insure proper moisture regulation during Phase I as follows: Add as much water as possible without run off at first two turns; add only enough during the next turn or turns to wet dry spots; and bring up to the desired moisture content (70 to 75%) by adequate watering just before filling. Phase Ishould be completed in 5 to 7 days, depending upon the raw ingredients used. At tray or bed fill?ing, add vegetable oil at rate of 110 US gallons (90 Imperial gallons)/4000 ft² of compost filled to a depth of 6 to 7 inches.

b) Phase II. Follow a proper temperature sequence during Phase II. Keep compost temperatures be?tween 140? and 115?F. Never allow recycling (re?heating) to occur. Provide for a proper pasteuriza?tion (140?F in the air and compost for a minimum of 2 hours) generally 1 to 2 days after filling. A 7-day period is the maximum duration required for a proper Phase II. The easiest and best way to accom?plish a proper phase II is to automate it. The Penn State Mushroom Test Demonstration Facility is such a system, and is described in Mushroom Science (IX:269-278, 1976).

2) Spawning. Use mixed spawning at the proper rate (one unit spawn for each 8 ft² of area is adequate for most operations). Thoroughly mix in delayed-release supplement at the rate of 5 to 7 percent of the dry weight of compost.

3) Spawn growing. Maintain compost temperatures between 73? and 79?F at all times; the closer to 75?, the better. Never allow compost temperatures to exceed 82?F. Maintain an adequate CO₂ level (between 6000 and 12,000 ppm) during the spawn-growing period. The compost should be fully grown and ready for cas? ing in 12 to 14 days.

4) Casing. Use the proper depth of casing layer; this varies, depending upon the casing material being used. For instance, a peat might require a casing layer depth of 1.75 inches, whereas a heavy clay soil might require only 0.75 inch to 1 inch depth. Insure proper treatment of the casing material to eliminate pests.

5)>Watering. I cannot descilbe a single watering method which will be best for all mushroom-growing operations - environmental conditions, cultural practices, and other things vary from operation to opera?tion, requiring modifications of the watering regime. However, the following general procedures should be followed: insure adequate initial water buildup im?mediately after casing. Bring casing layer back up to its water-holding capacity just prior to first break by adequate waterings. Between breaks, insure ade?quate buildup of water in the casing layer to meet the water requirements of the next flush.

6) Ventilation after casing. Provide for relatively high initial CO₂ levels (5000 to 10,000 ppm) until the mushroom mycelium reaches the surface of the cas? ing layer. Reduce the CO₂ level immediately there? after to 600-1200 ppm depending upon the strain of spawn being used) for proper pinning. After pins are setandbegintoenlarge,adjustCO₂ levelto 1500-2000 ppm (depending again on strain) for en? largement of first break and the remainder of crop? ping.ManualCO₂ samplingandadjustmentof dampers to control CO₂ levels is satisfactory but au? tomation as descrlbed at the Penn State Mushroom TestDemonstrationFacility(MushroomScience IX:269-278, 1976) is feaslble and may be better suited for some operations.

7) Cropping. Practice good disease prevention by fol? lowing a few simple rules:

a) Pick mushrooms closed - never allow open mushrooms around the plant.

b) Maintain a good benomyl program - according to approved label instructions.

c) Maintain a good zineb dusting program - ac? cording to approved label instructions.

d) Employ a good general sanitation and spot-treat? ment program. Keep picking utensils clean, always pick newest rooms first, etc. Spot treat infection centers of Verticilium, Mycogone, Trichoderma, etc., with 15% HTH powder immediately.

e) Maintain a good fly-control program by follow? ing current legal and recommended practices.

Let me close with a little philosophy. I have observed that severe difficulties are encountered in mushroom growing when decisions on the adoption of new in?novations in mushroom culture were based solely on the following three reasons - rather than on the needs of the mushroom:

1) To accommodate the labor force.

2) To accommodate mechanization and/or materials handling.

3) As a short-term economic expediency.

Summary

Efficient mushroom production can be achieved by taking a new look at "old" methods. Steady progress has been and will continue to be made in mushroom production due to the intelligent and practical appli?cation of sound research findings by dedicated mush?room growers.