"Great Summer" is on July 23rd or 24th every year, when the sun reaches the longitude of the Yellow River120. Twenty-four solar term: "In mid-June, ... the heat is also hot, which is divided into small and large, small at the beginning of the month and large in the middle of the month, and now it is hot in Judah." At this time, it is the hottest period in a year, with the highest temperature, the fastest growth of crops, and the most frequent droughts, floods and windstorms in most areas. It is very important to grab crops and seeds, prevent drought and drainage, and manage fields.
In ancient China, the great summer heat was divided into three periods: "The rotten grass was firefly; Second, wait for the soil to moisten the summer heat; When it rains, it will be fine. " There are more than 2,000 species of fireflies in the world, which are divided into aquatic and terrestrial species. Terrestrial fireflies lay eggs on hay, and when it is hot, fireflies ovulate, so the ancients thought that fireflies were made from rotten grass. The second weather is that the weather is getting muggy and the land is wet. The third weather is that there are often heavy thunderstorms, and this heavy rain weakens the heat and humidity, and the weather begins to transition to beginning of autumn.
"It's yellow day and night in the hot summer". For the areas where double-cropping rice is planted in China, the "double grab" battle, which is the most intense and arduous in a year, has begun. As the saying goes: "Early rice grabs the sun, late rice grabs the time", "No mowing in the summer, one reed is missing a day", and harvesting early rice in time can not only reduce the harm caused by the wind and rain in the later period, but also ensure a high yield and harvest, and make it possible to plant and transplant in time for two nights to strive for sufficient growth period. According to the change of weather, we should arrange flexibly, cut more on sunny days and plant more on cloudy days. We should finish planting for two nights before the end of July, and not later than beginning of autumn at the latest. "In hot summer, not a brick is dried for three days". In hot summer, water evaporates very quickly, especially in the middle and lower reaches of the Yangtze River during the summer drought period, and the demand for water by vigorously growing crops is more urgent. It is really "a little summer rain is like silver, and a big summer rain is like gold." The leaf area of cotton during flowering and bolling reaches the maximum value in its life, which is the peak period of water demand. It is best to require the soil moisture in the field to account for 70% ~ 80% of the field capacity. If it is lower than 60%, it will lead to the flowering and bolling, so it must be irrigated immediately. It should be noted that irrigation should not be carried out at noon when the temperature is high, so as to avoid the excessive change of soil temperature and aggravate the shedding of buds and bolls. Soybean flowering and pod setting is also the critical period of water demand, which is very sensitive to water shortage. The agricultural proverb says, "When the soybean blooms, the shrimp is touched in the ditch." If there is a drought, it should be watered in time.
Summer maize in Huanghuai Plain has generally been jointing and heading, and it is about to heading, which is the most critical period for yield formation, so we should guard against the harm of "neck drought".
"Rice smiled in the field and people jumped in the room." High temperature in midsummer is very beneficial to crop growth, but it has obvious adverse effects on people's work, production, study and life. Generally speaking, in the hot days when the maximum temperature is higher than 35℃, there are obviously more people suffering from heatstroke; In the hot days when the maximum temperature is above 37℃, the number of people suffering from heatstroke will increase sharply. Especially in the middle and lower reaches of the Yangtze River under the control of subtropical high, the sun is like fire, the wind is small and the humidity is high, which makes people feel sultry. Nanjing, Wuhan and Chongqing, the three famous stove cities along the Yangtze River in China, have as many as17 ~ 34 days and 3 ~14 days on average every year. In fact, there are still many places hotter than the "three stoves", such as Anqing, Jiujiang and Wanxian. Among them, Guixi in Jiangxi, Hengyang in Hunan and Kaixian in Sichuan have an average hot day of more than 40 days. The whole middle and lower reaches of the Yangtze River is a big stove, so it is particularly important to do a good job in heatstroke prevention and cooling. In addition, many kinds of crop pests are active in summer, so special attention should be paid to personal protection when applying pesticides at high temperature to avoid poisoning accidents.
Summer heat means hot. It shows that it is the hottest solar term in a year.
Generally speaking, the summer solar term is the period with the most sunshine and the highest temperature in South China, the period with the most abundant rainfall, the most common thunderstorm and the most concentrated days with high temperature above 30℃ in the west of South China, and the period with the most frequent occurrence of high temperature above 35℃ in the east of South China.
The high temperature before and after the Great Summer is a sign of normal climate, because higher temperature is beneficial to flowering and filling of crops in Da Chun. However, if the temperature is too high, the growth of crops will be inhibited, and the seed setting rate of rice will drop obviously. Light, heat and water are at the peak of a year after the western part of South China falls into the rain, which promote each other and form good climatic conditions for crop growth in Da Chun, but attention should be paid to flood control and drainage. In the eastern part of South China, high temperature and long sunshine are often accompanied by little rain, which will not only limit the exertion of light and heat advantages, but also aggravate the adverse effects of summer drought on crops in Da Chun. In order to resist summer drought, besides paying attention to water storage in the early stage, crop cultivation measures should be improved according to the climatic characteristics of eastern South China, so as to gain advantages and avoid disadvantages.