"Wheat can't reach Mangzhong Valley until autumn, and sweet potatoes can't be harvested until after the cold dew". How to harvest sweet potatoes?

"Wheat will not reach Mangzi Valley until autumn, and sweet potato will not be harvested until after cold dew", which is an agricultural proverb about the harvest time of triple cropping crops. In rural areas, there are many agricultural proverbs like this, which also contain the practical experience summarized and condensed by several generations of old farmers in their long-term production and life. Experience is to be learned and used for reference, but it is not and should not be copied mechanically. The so-called world changes with time, place and environmental conditions. It is sometimes very important to make necessary compromises and adaptations according to the actual situation.

Still use the agricultural proverb "Wheat is planted in the valley until autumn, and sweet potatoes are harvested after the cold dew", in which sweet potatoes don't have to wait until the solar terms enter the cold dew.

Sweet potato, a crop, likes temperature and is afraid of cold. When the ground temperature of 5- 10 cm is around 10℃, the cut sweet potato seedlings will not take root, and only when the temperature reaches 15℃, the cut sweet potato roots will be normal at 17- 18℃. The optimum temperature for the growth of sweet potato vine leaves is 2 1-26℃. The growth stopped below 65438 05℃ and was inhibited above 38℃. The minimum temperature required for potato expansion and growth is 16- 18℃, and the optimum temperature is 22-25℃. When the temperature is 25-28℃, the stems and leaves of sweet potato grow rapidly. When the temperature is above 30℃, the stem and leaf of sweet potato grow faster, but the tuber expands slowly. When the temperature rises above 38℃, the respiration consumption of sweet potato plants is more, and the growth of stems and leaves is slower. On the other hand, when the temperature drops below 20℃, sweet potato stems and leaves grow rapidly, and the growth of sweet potato stops at 15℃. When the temperature drops below 10℃, sweet potato may suffer from chilling injury, so it is not suitable for storage after harvesting.

According to the above growth law of sweet potato, sweet potato in cellar should be harvested when the ambient temperature drops to 65438 05℃, and generally it should be harvested before the ambient temperature drops to 65438 02℃. The sweet potatoes harvested that day should be put into the cellar that day. When the temperature is chosen as the sweet potato harvest time, it is best for northern potato farmers to harvest sweet potatoes in their fields before the first frost. But this is only a date reference standard, and everything still depends on the specific temperature changes.

As a potato farmer who grows sweet potatoes, we should know that the cold dew solar term is the turning point of climate change in many areas. Often after a cold wave storm, the daily average temperature may drop by 8℃- 10℃. Sweet potato harvest must take into account this sudden weather situation, take precautions in advance, and can't cram for the Buddha's feet temporarily. Once the solar term enters the cold dew, the average temperature in some parts of the northwest and the north-central part of the northeast often drops below 8℃. The temperature in the southeast, North China and Huanghuai will also drop to 8- 16℃. In summer, even if you don't go out of Jianghuai and Jiangnan, the general temperature will not exceed 15-20℃, and the average temperature in some plateau areas of Qinghai Province has even dropped below 0℃. The temperature conditions and the time of temperature change are different in different places, so the specific time of sweet potato harvest needs to be mastered flexibly. Even if the solar term is not cold, considering the local reality and special weather conditions, the early harvest of sweet potatoes can not be postponed.

The different uses of sweet potatoes should also focus on the grasp of harvest time. Sweet potato used for dry potato and starch processing should be harvested at an appropriate time after starch accumulation is sufficient. At the beginning of harvest, the swelling time of root tuber is shortened, and the time of nutrient accumulation is naturally shortened, so the yield of root tuber and final starch of sweet potato will be relatively reduced. However, if the harvest is too late, the starch contained in the sweet potato block will be hydrolyzed and converted into sugar and water, and the starch yield will still be reduced after harvesting and processing. If sweet potatoes are to be sold as fresh food, we should consider the price and income. In the early harvest with high market price and good benefit, we should not blindly ignore the traditional time and temperature.