Potato Review

10 POTATO REVIEW NOVEMBER/DECEMBER 2020 STORAGE Ventilate and regulate Eric Anderson, Senior Agronomist at Scottish Agronomy, suggests some key issues to be thinking about ahead of potato storage this autumn. F OR seed, using positive ventilation is accepted as best practice. Normal ventilation rates for box stores are typically designed to be 0.02 m3/s/t but this rate of air ow is primarily to aid distribution, rather than that required to remove transferred heat and moisture. e best way to deal with excess moisture on the surface of harvest tubers in boxes is with positive ventilation systems. Positive ventilation with box stores need up to 0.08 m3/s/t to allow for air leakage. Positive systems require fans which can act against a modest system pressure but they still make up the minority of box storage ventilation systems. However, it might be argued that they are the best available solution to many of the problems currently experienced in box stores with air ow. e letterbox is the most common type but the size of this system is usually restricted to around 10 boxes deep from the duct by the amount of air than can be delivered through the relatively small pallet slots. Use the highest air ow rate available for drying. Batch systems are well suited to drying as air ow can concentrate on a small tonnage. Letterbox systems are generally limited to eight to 10 boxes deep for e ective drying. True letterbox systems can be set up by building a plenum at the back of the boxes, facing it with plywood and cutting slots to line up with alternate pallet slots. Air is delivered into the plenum, through the open slots and under the boxes to the far end of the stack where the opening is closed o using foam bungs. e closed slot means air has to travel up through the box above and down through the box below to exit via the next pallet slot. e suction wall system, where air is sucked through the slatted ends of boxes, is also increasing in use. It is a more adaptable but less space-e cient ventilation method in that it can be used even when the store is part- lled. “Using outside air that is cooler than the tuber temperature is ideal but try to avoid bringing in outside air warmer than the temperature of the tubers already in store.” e system is again based around a plenum at the back of the store but, in this instance, it is connected to a series of covered voids between the columns of boxes, from which air is extracted. Suction wall systems are more suited to stores with more than 10 boxes per row. e aim is to dry the tubers and remove eld heat whilst avoiding condensation, and promote wound healing. If using a letter box system with a rotation of boxes, a period of at least two to ve days of positive ventilation is required at a holding temperature of 10 to 12°C (or longer if temperatures are lower than this) to reduce the bacterial and fungal infection risk. Using outside air that is cooler than the tuber temperature is ideal but try Eric Anderson, Senior Agronomist at Scottish Agronomy.