What are the climatic characteristics of "slight cold and severe cold"? What is the impact on agriculture?

During the slight cold, the daily average temperature in the middle and lower reaches of the Yangtze River is 1 to 3 degrees, and it is below zero in Jiangbei. The snowfall or rainfall 10 mm to 30 mm. The severe cold is the coldest season in a year, and then it will be the "three-point water heating" beginning of spring. The daily average temperature in the middle and lower reaches of the Yangtze River is 1 to 3 degrees, and the snowfall or rainfall is10mm to 30mm ... The main farming activities are: storing fertilizer, making fertilizer, repairing water conservancy in winter, planting trees, cleaning and transforming fish ponds, etc.