Potato Grower

November 2017

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38 POTATO GROWER | NOVEMBER 2017 Diggin' In Diggin' In Diggin' In Diggin' In Diggin' In Diggin' In STORAGE | By Nora Olsen and Mary Jo Frazier, University of Idaho Managing weight loss in storage Weighing In By now, potatoes in most of the U.S. have been in storage one to two months. The crop is at or nearing holding temperatures specific to the cultivar and use. Storages are being monitored for disease development, desired temperature, ventilation and humidity. What isn't as easy to see is the amount of weight loss, or shrinkage, that is occurring in storage. Stored potatoes will lose weight from respiration (carbon and water loss), transpiration (direct water loss), and disease. Transpiration water loss is the greatest factor in weight loss unless high levels of disease are present—then that becomes the greatest contributor— Eastern Idaho Ag Expo Idaho Potato Conference For More Information Call 208-939-6426 39 th Annual 50 th Annual 39 th Annual Eastern Idaho Ag Expo Jan. 16-18, 2018 HOLT ARENA Pocatello, ID Tuesday - 9 a.m.- 5 p.m. Wednesday - 9 a.m.- 5 p.m. Thursday - 9 a.m.- 1 p.m. 50 th Annual Idaho Potato Conference and Trade Show Jan. 17-18, 2018 I.S.U. Student Union Building Pocatello, ID Wednesday - 8 a.m. - 5 p.m. Thursday - 8 a.m. - 12 p.m. 168981SpePro13s.indd 1 9/8/17 12:30 PM especially if caused by any of the water rots. Some of the factors that affect weight loss include cultivar, status of the tuber (e.g., skin set, stress, hydration level, pulp temperature, wounds/ bruises, rate of wound healing), disease, sprouting, duration in storage, and storage structure, management and conditions (temperature, humidity and ventilation). That is a long list of factors that contributes to weight loss and managing the complexity can be difficult, but knowing what contributes to the greatest weight loss of your crop can help minimize losses. Unfortunately, the greatest weight loss has likely already happened—about the first 30 days in storage—and then it decreases as potatoes are held for the bulk of the storage season. The reason the first few weeks in storage result in the greatest weight loss is due to high rates of respiration, higher pulp and storage temperatures promoting greater transpiration water losses, and typically a greater vapor pressure deficit in trying to equilibrate the pile. Later in storage, there can be an increase in weight loss due to breaking of dormancy, rise in storage temperatures, and disease development. In small-scale research trials, weight loss was dependent upon initial curing temperatures, and 55 to 70 percent of the total weight loss occurred in the first 30 days (Figure 1). In general, about 3 percent weight loss was seen in the first month. Total weight loss after five months was about 5 percent. Tuber conditions and early storage management can greatly affect initial weight loss. To get an idea of how much weight loss can be seen in commercial buildings, for the last several years the University of Idaho has put captured bags with 20 to 30 pounds of potatoes in various areas of the bulk pile. Number of bags per storage ranged from eight to 32. Each sample bag was weighed and pulp temperatures determined as loaded into storage. The sample bags were re-weighed and evaluated for rot when the storage was unloaded. The difference in pre- and post- storage weights was the percent weight loss for the storage season. This is an

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