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How to Manage The Watering of a Mushroom Crop

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#1 Hippie3



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Posted 21 November 2007 - 10:28 AM

How to Manage the Watering of a Mushroom Crop
By Paul J. Wuest

Mushroom quality and speed of production are affected by casing depth, moisture, and watering. The initial moisture content of casing, as well as how and when water is applied, affects the number of pins that form and the size and quality of the mushroom. Water and watering are frequently THE FACTORS that separate excellent growers from average growers, and (as might be implied), can seem confusing if the overall goals of watering are not fully understood or implemented. Before getting into the watering, a few statements about the casing layer are in order.

Normally a depth (measured after initial water has been applied) of 1 to 1.25 inches of casing is adequate for most mushroom crops.
[This assumes substrate depths of 3+ inches,
thinner substrates do fine with 1/2 inch of casing]
There are growers and farms where casing depth will be as much as 1.75 to 2 inches, but such depth is usually found only where peat moss is the casing medium. There is nothing inherently wrong with a deep casing layer, but with good management there is no need to use so much casing. Further, the deeper the casing the longer the interval between casing and picking. More could be said about casing, but this general guideline is adequate to bring on satisfactory crops.

Watering the casing is an art, in that growers must i) judge when to water, ii) decide how much water is needed, and iii) know how to apply the water. The following comments are suggested as factors to be considered about watering, rather than an all-inclusive watering schedule.

How to Apply Water
Before discussing when to apply water, it is important to mention how water should be applied and the work habits of the person applying water. A roseface (water-break) spray head is needed to water mushroom casing. It is desirable that the roseface produce a very fine stream of water in a rather long high arc
for the initial waterings; the potential for sealing the casing by the force of the water is thus minimized. A roseface with 750 to 1000 holes 0.01 inch in diameter is quite acceptable for the task
How a person applies water depends on initial training and level of supervision. Some successful growers train watering personnel to move the rose-face constantly, from left to right and right to left, perhaps three passes per 4 feet of bed, watering one-half the width of the surface. Once a person has developed a movement pattern, a cadence of "l,"2,"3" can be followed for applying water. Experience suggests that use of a cadence during watering is a technique whereby a manager can direct how much water should be applied. This means that during the count of "1," water is directed from left to right starting at the center of the bed. Between the counts of "1" and "2," the rose is moved from the right to the left a bit closer to the sideboard, and between "2" and "3" the final swipe is made, even closer to the sideboard and in the opposite direction. Directing the water from the center to the sideboard means that the person watering must move the spray head in or out to assure that the water is aimed at the target area.

Sealed Casing and Scratching
Casing will seal if the water falling on it falls with too much force or if too much water is applied at one time, or a combination of the two occurs. The person doing the watering must invert the roseface so that it points up and away from the casing, rather than pointing directly at the casing surface. This procedure dissipates the energy behind the water by forcing the water through an arc-like trajectory before the water falls gently onto the casing. The most common failures during watering are i) the roseface is not moved quickly enough over the casing surface, ii) the movement is not rhythmic and uniform, and iii) there is too much overlapping of the watered area. Once casing is sealed (becomes nonporous), mushroom production will be drastically reduced or delayed;
neither is desirable.
Some growers find it necessary to scratch the casing surface following initial applications of water because the casing is sealed. Sealing is common when peat is used, especially when the peat is applied by a belt-fed casing machine. Scratching is recommended by some growers; others avoid the practice. A rule of thumb when scratching the casing is to restrict scratching to the depth where spawn has not grown. Scratching casing that contains spawn damages the mycelium, and this restricts the size of the developing mushrooms and may cause mushrooms to form under the casing. Scratching works for some farmers and not for others, so scratching is not a practice recommended for all mushroom operations.

When to Water
Initial water is applied immediately after casing, or at least during the first or second day after casing, and additional applications of water are continued - as frequently as the structure of the casing permits - for a few days until the casing contains as much water as it can hold. This volume of water is referred to as the water-holding capacity. It is essential that the casing receive all the water it can hold at this time, for the casing must always be moist from bottom to top, that is, from its surface to where it contacts the compost. As the spawn enters the casing, it will absorb water. The spawn grows from the compost up through the casing, so the casing initially dries more rapidly closer to the compost than elsewhere. If casing is allowed to dry a good bit, it will lose its ability to absorb water. When this occurs, it will no longer act as a water reservoir, mushrooms borne upon it will be soft and pithy, and yields will be reduced. When too much water is in the casing, spawn growth slows or stops -with resultant production delays or spawn death.
A radical way to apply initial water to peat casing is to flood the casing. In a day or so after the water is absorbed, scratch the peat to break up the crust and restore texture to the casing; this method is used immediately after casing and not during cropping. It is suggested that this method of watering be tried and evaluated in a small area before using it throughout an entire growing room.
After initial waterings, it may be necessary to water lightly, mist, or fog until pins appear. Where such a light amount of water is to be applied, the cadence during watering should be increased from "1"— "2"—"3" to perhaps "1"-"2"-"3" or even "1,""2,"3," but the movement pattern of the rose-face does not change. These numbers and dashes are used to give an idea of the speed at which the arm of the watering person moves. Precisely when to water and how much water to apply when bringing on first break is something that has to be learned - and it's usually
different for each cultivar.

Watering Different Cultivars
White mushrooms are capable of withstanding heavy waterings when the pins are about the size of a pencil eraser (approx 0.25 inch) in diameter. Watering a cream cultivar at the same rate will destroy most of the pins. Cream mushrooms must have pins that are at least twice that size (about 0.5 inch) before large quantities of water can be applied. The rough-white mushroom is closer to cream than to white cultivars in terms of tolerance to watering. It is possible to apply too much water too early with either the cream or the rough-white cultivar and thereby destroy the pins.

How to Apply Enough Water
When the first water of the day is applied at a fast cadence, a second heavier watering can be applied without as much chance of sealing the casing. Delay is essential when applying more than one watering per day, for the casing absorbs the first water and binds it, and thus becomes physically conditioned to accept more water; binding of water usually requires 3 to 5 hours. Once the initial buttons develop and thereafter during cropping, a roseface that provides a-coarser water stream (1000 to 1300 holes of 0.02 inch diameter) can be used. The mushrooms and buttons break part of the force of the water and the extensive rhizomorph formation holds the casing, so sealing is much less likely to occur, even with a coarser roseface.

Watering During the Crop
The speed at which a crop grows, i.e., the time interval between breaks, becomes a decisive factor in deciding when to water and how much water to apply. The speed of the crop is affected by compost and air temperatures. If a break is coming on quickly, water must be applied quickly and early, perhaps as early as the last two picking days of the previous break. When a break develops slowly, then it may be desirable to apply the water more slowly and over a longer period. Under no circumstances should a casing be allowed to dry out completely. If the casing becomes dry, the only way to re-moisten it is by very light repetitive waterings. If casing with an active spawn growth dries out, the mycelium seems to surround the soil or peat particles in a way that prevents water adsorption. The casing has the appearance of harboring a grey mold, but actually it is spawn.
Mushrooms growing on dry casing tend to show water-stress symptoms. They are light and pithy (spongy) and the veils tend to be stretched. The cap bottoms appear to be perpendicular to stem since the cap is not fully rounded. Mushrooms harvested from casing too dry during one stage of their development will have a good bit of casing attached to them; this is especially true of first-break mushrooms.
How much water should be added after first break? A quasi-analytical rule may be used to determine this. Mushrooms are about 90 percent water, so a pound of harvested mushrooms per square foot of bed means that 0.9 lb of water has been removed from that same square foot. If an additional pound is expected on second break, then 0.9 lb of water has to be replaced, plus a bit more for evaporation. This quantity is needed only for second break, since subsequent breaks normally are not as heavy. A gallon of water weighs just a bit more than 8 pounds; the Imperial gallon will weigh close to 10 pounds. After calculating the total pounds of mushrooms harvested (lb/ft2 times the total harvested area - in square feet), you can calculate the volume of replacement water by taking nine-tenths of this figure and dividing it by 8 (US gal) or by 10 if you're using Imperial gallons.

Water, Temperature, and Cropping
A scenario of what a grower will see and what should be done as a crop is developing will bring a number of factors together to make a total picture.
The compost has been cased for 8 to 10 days and the air temperature has cooled to 60°F; compost temperature is in the lower 70s. Fresh air going into the room causes the room air to smell fresh, the mycelium is knitting together, and pins are starting to form. If the casing tends to dry, a quick "1,"2,"3" watering cadence is needed to prevent its becoming overdry; fogging the casing surface every second day is an alternative, and floors and walls should be soaked routinely to minimize drying. A few days later, when the pins of a white cultivar are about the size of a pencil eraser, the first in a series of first-break waterings begins. Morning and afternoon waterings are applied in the "1"-"2"-"3" cadence. If a cream cultivar is being grown, water is not applied at this time; a delay of about 2 days will give the pins time to grow to twice the size of a pea. After the initial first-break watering, water will have to be applied two, three, or as many times as needed so the casing remains at its moisture-holding capacity while the pins of the first-break mushrooms develop into buttons. If
a heavy break is developing, additional water may be applied from the button stage up to the onset of harvesting. Watering should be avoided during the harvest period; quality usually suffers.
Second-break pins form before first-break mushrooms are harvested. Water needs to be applied towards the end of first break since the harvested mushrooms absorb much of the water in the casing. If compost or air temperatures cause the crop to break on a short interval - 4 or 5 days - quite a bit of water must be added before the end of the first-break harvest. Too much water applied to a cream or an off-white cultivar at this time will cause a great number of dead pins, depressed yields in third break, and practically no production at all during fourth break.
Once second break pins have matured into small buttons, heavier applications of water can commence. These should be continued until the casing again reaches a good moisture level. Repeated waterings during a single day are far better for the crop than single waterings on successive days. At the same time, too much water applied at one time or too much water applied over a 24-hr period can result in dead or dying pins, especially with off-white and cream cultivars. Many growers notice the abundance of dead pins after second break and erroneously think it to be a symptom of a virus condition, rather than of water damage. Less water is needed with each successive break, and the casing must be" moist, but not wet. This requirement can usually be met by watering fourth and subsequent breaks no more frequently than twice weekly, preferably waiting until buttons have developed.
Overwatering can result in the death of pins and small mushrooms, and underwatering or poorly timed waterings produce soft, poor-quality mushrooms. Most growers learn through experience how to water, which roseface to use, and the frequency of water applications as the crop matures. The guidelines presented here cannot substitute for a keen sense of observation and experience with how different cultivars respond to different watering patterns. When a watering pattern is changed, a wise grower will record the changes, along with information about how the mushrooms look before and after the water was applied. Such a reference can be useful in making decisions about future crops.

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