Potato Grower

36 Potato Grower |DECEMBER 2015 Ask your Milestone representative about early order incentives for 2016 equipment! 395 W Hwy 39, Blackfoot ID Phone: 208-785-4285 Toll Free: 800-574-1852 Fax: 208-785-1060 info@milestone-equipment.com www.milestone-equipment.com Available Widths: 84" 72" 60" 48" 36" 156271Milest13h.indd 1 10/13/15 8:23 AM diggin' in STORAGE By Garry Isaacs Making Weight Creating the perfect storage atmosphere Potatoes are sold by weight. Weight loss is directly related to profit and it can represent as much as a 15 percent reduction or more of the bottom line. Pressure bruise, largely the result of dehydration of tubers, also decreases the value of potatoes. Experts have discovered that diseases such as silver scurf can also contribute to dehydration, shrink and weight loss. Silver scurf and other fungi grow rapidly on wet surfaces: "Silver scurf may have a transient effect on potato growth and tuber yield" (Mooi, 1968; Denner et al., 1997). "The light brown lesions (silver scurf) increase the permeability of the tuber skin, causing shrinkage/water loss and therefore weight loss" (Hunger & McIntyre, 1979; Read & Hide, 1984). Relative humidity is the amount of water contained in air relative to the air temperature. It is measured by checking the difference between dry bulb and wet bulb temperatures of the air. Water content of potatoes in storage is directly related to the water content of the storage air. Dry air causes potato weight loss because the moisture is drawn out of potatoes toward equilibrium with the water content of the storage air. Potato storage air should constantly be maintained between 95 and 99 percent relative humidity at all times if possible to limit pressure bruise and to keep potatoes from shrinking by dehydration. "If weight loss is compared over six months of storage at various relative humidity levels, potatoes stored at 90 percent relative humidity could lose 9 percent in weight, or nearly twice as much weight as those stored at 95 percent relative humidity," says University of Idaho Extension potato storage specialist Nora Olsen. "Given a storage capacity of 100,000 hundredweight and a value of $5 per hundredweight, the building maintained at 90 percent humidity would return $22,000 less than the storage controlled at 95 percent relative humidity. The impact of maintaining the proper relative humidity cannot be overstated." RELATIVE HUMIDITY IS INVISIBLE TO THE EYE It is important for storage managers to understand that at 64 degrees Fahrenheit, the air will only hold about 15 grams of water per cubic meter of air space (0.42 grams of water per cubic foot of air). As the temperature drops, the air will hold less and less water. At 42 degrees, the atmosphere only holds about 5.5 grams of water per cubic meter of air. Air at 53 degrees will contain almost twice as much water (10.4 grams per cubic meter) than air at 42 degrees (5.5 grams per cubic meter). For instance, a storage building with an area of 60 by 150 feet and 18 feet high contains 162,000 cubic feet—about 4,576 cubic meters—of air space. A gallon of water weighs about 3,785 grams. Total water saturation of the air space of this empty building at 42 degrees would be achieved with only a total of about 6.65 gallons of water. If the air space remaining after a building is full of potatoes is 25 percent, the total amount of water that the air space will hold at 42 degrees is less than 2 gallons. If more water could be added to the air space, it would leave the air and things would begin to get wet. Cold surfaces on building walls or beams will also lower humidity by condensation. This causes the drip lines commonly seen below the beams of a storage bin. Whenever condensation happens, the air in the storage is giving up water and is becoming drier. The colder the air, the drier the air, and the more potatoes will shrink. KEEP THE OUTSIDE OUT What may be considered a beautiful day outside the cellar is not nearly cool or humid enough to keep stored potatoes in good shape.

• Cover