Detailed Explanation of Key Techniques for Overwinter Storage of Sweet Potatoes

As a natural green food, the unique health benefits of sweet potatoes are gradually being recognized, and the planting area of sweet potatoes is also increasing. Therefore, the safe overwinter storage of fresh-eating sweet potatoes and off-season sales bring considerable economic benefits to sweet potato farmers. Unlike other food crops, sweet potatoes have roots containing a large amount of water. With reasonable measures, they can be stored for more than 8 months with a 96% intact rate, while with poor preservation they will rot in about 20 days. To prevent fresh-eating sweet potatoes from rotting in the cellar, extend the storage period, and achieve value growth, the following aspects must be handled well.
1. Cellar disinfection. The methods of preserving sweet potatoes vary from place to place, with the most commonly used being cellar storage. The cellars for storing sweet potatoes are diverse, such as well cellars, shed cellars, buried cellars, and so on, but the management measures are roughly the same. Before the sweet potatoes are put into the cellar, the interior of the cellar should be disinfected. Half a month before harvest, open the cellar door for ventilation, then remove a layer of old soil from the four walls and the floor inside the cellar. Then spray formalin at 0.5 kg diluted in 25 kg of water on the surrounding walls, floor, and cellar ceiling, or fumigate with sulfur 2 times, to eliminate pathogens such as black rot and soft rot.
2. Timely harvest. According to the growth pattern of sweet potatoes, generally when the temperature is below 18°C, the stems and leaves stop growing, and when the 10 cm soil temperature is below 20°C, the root weight actually decreases. In North China there is a saying: "Cold Dew is too early, Start of Winter is too late, before frost, it is just right," meaning harvesting must be completed before Frost's Descent, when the temperature is above 10°C, to ensure the sweet potatoes are not cold-damaged in the field.
3. Careful harvesting, careful selection, and timely cellaring. When harvesting, choose a windless sunny day, and complete harvesting and cellaring on the same day; do not let the tubers stay overnight in the field. Achieve careful harvesting and careful selection, which can be summarized as "four gentles, five don'ts." That is, dig gently, load gently, transport gently, and place gently, to reduce bruising of the tubers and opportunities for disease infection; do not take those damaged by frost, do not take those with disease spots, do not take those with severe breakage, do not take water-soaked tubers, and do not take those left exposed in the open for too long after harvest. Do not fill the cellar too full; generally fill only one-half, and at most do not exceed two-thirds, to facilitate ventilation and air exchange. In addition, dilute 50% compound carbendazim to a 500-fold solution and spray it to disinfect and sterilize the tubers, and the storage effect will be somewhat better.
4. Management of the sweet potato cellar. The storage environment for sweet potatoes requires relatively high humidity, and temperature changes must be strictly controlled; above 18°C they easily sprout, and below 10°C they easily rot. Throughout the storage period, the cellar temperature should be controlled at 10-14°C, with the most suitable temperature between 11-13°C. If the humidity is too low, the tubers easily shrink and become pithy; if the humidity is too high, it easily leads to the reproduction and spread of pathogens and causes pathological rot. The optimal humidity for sweet potato storage is 80%-95%. When the relative humidity in the cellar is below 80%, it causes sweet potatoes to lose water and wilt, and eating quality declines; when the relative humidity is above 95%, although respiration decreases, microbial activity is vigorous, and they are susceptible to disease. The first 20 days or so after cellaring is the sweating period, when fresh sweet potatoes respire vigorously, releasing a large amount of water and heat; the cellar temperature is high and humidity is high. During this period, pay attention to ventilation and air exchange, reduce temperature and dissipate moisture, and when necessary use an exhaust fan to exhaust air and cool down. From 20 days after cellaring to early February of the following year is the middle period; at this time the temperature is low and cold damage is likely, so attention should be paid to keeping warm and maintaining a suitable temperature in the cellar. After the Start of Spring, when the temperature rises, ventilation should be carried out in a timely manner according to weather changes, so that the highest temperature in the cellar does not exceed 18°C.
In short, sweet potato storage management is a very complex task with strong technical requirements, requiring management personnel to have a strong sense of responsibility and to be careful and serious in their work. Do a good job in every link throughout the storage process, check frequently, promptly remove rotten tubers when found, and promptly solve problems when found, to ensure the safe overwinter storage of fresh sweet potatoes.