How big is the impact of a late spring cold snap on agricultural production?

Starting in April, under the influence of relatively strong cold air, a large-scale precipitation event occurred in the central and eastern regions of China, accompanied by a sharp drop in temperature from north to south. In some areas of the middle and lower reaches of the Yangtze River, an obvious "late spring cold snap" occurred. So, what is the cause of this weather this year? What impact does a "late spring cold snap" have on agricultural production? How can the harm caused by this weather be prevented? A reporter interviewed Niu Ruoyun, a professor-level senior engineer at the National Meteorological Center, and Song Yingbo, a professor-level senior engineer at the Agrometeorological Center of the National Meteorological Center.

According to experts, a "late spring cold snap" refers to a weather phenomenon in which temperatures rise relatively quickly in early spring and then a period of relatively low temperatures occurs later. But it should be noted that this definition is only a conventional one. Because China is vast, climates differ from place to place, crops grown differ, and the values of meteorological factors affecting crop growth differ. For example, Hunan has its own definition of a "late spring cold snap," and Yunnan also has Yunnan's definition of a "late spring cold snap." The specific indicators depend on the specific conditions in each place.

The meteorological indicator for a "late spring cold snap" in southern China commonly used in agriculture refers to the daily average temperature dropping below 12°C and lasting for 3~5 days. Taking this weather event as an example, the values of meteorological factors in the middle and lower reaches of the Yangtze River reached this indicator, so it can be determined that a "late spring cold snap" occurred in the corresponding areas.

So, what impact will a "late spring cold snap" have on current agricultural production?

Experts said that when a "late spring cold snap" suddenly occurs against the background of continuously rising temperatures, and the temperature drop is relatively large, it will have a certain adverse impact on crop growth, among which the impact on early rice is relatively obvious.

During this cooling process, early rice in the middle and lower reaches of the Yangtze River was at the stage of sowing and seedling raising. If preventive measures are not taken well, the sudden "late spring cold snap" will cause seed rot and seedling rot in early rice. In addition to early rice, cotton at the sowing stage is also susceptible and may show seed rot and dead seedlings. As an autumn-sown crop from last year, rapeseed flowering and pollination will also be affected, which will lead to a certain reduction in later yield.

If ranked, the crop most affected by a "late spring cold snap" is early rice, followed by cotton at the sowing stage, and then rapeseed.

During this "late spring cold snap" weather process, the average temperature in South China did not drop below 12°C, and most early rice in South China was already at the three-leaf to transplanting-and-green-returning stage. The cooling had no obvious impact on early rice growth. In the north, although the daily average temperature in many areas was below 12°C after the cooling, because local crops differ from those in the middle and lower reaches of the Yangtze River, the indicator for measuring whether it is a "late spring cold snap" is also different, so the 12°C indicator cannot simply be applied, but it can be used as a reference indicator. For the northwest, north China, and Huang-Huai regions, when the daily minimum temperature is below 2°C, a "late spring cold snap" can also occur, which may cause winter wheat, fruit trees, vegetables, and other crops to suffer frost damage. From this perspective, the impact of this cooling on crops in northern regions is relatively small.

Experts suggest that corresponding measures can be taken in agricultural production to defend against a "late spring cold snap." For early rice seedling raising, plastic film can be added over the shed. At present, there are mainly two methods of early rice planting: one is direct sowing in the field, and the other is first raising seedlings in a small field plot and then transplanting the seedlings into the field. When a "late spring cold snap" arrives, if early rice is still in the seedling-raising period, the film of the early rice seedling-raising shed needs to be reinforced. Areas with conditions can cover with double film to keep warm and protect the seedlings; at the same time, phosphate fertilizer can be appropriately sprayed before the temperature drops to enhance the stress resistance of rice seedlings and prevent cold air from causing seed rot and seedling rot in rice.

For direct-seeded early rice, preventive measures should be taken according to local conditions. If seeds have not yet been soaked, sowing should be postponed to avoid seed rot and seedling rot caused by low temperature and continuous rain; for rice seeds that have already been soaked and sprouted but not yet sown in the field, the sprouts should be spread thin and aired, and sowing should be seized in time on clear days during the "end of cold, beginning of warmth" when the weather improves; for rice fields that have already been sown, drainage should be strengthened to prevent long-term flooding from causing root rot and sprout rot; for rice fields where seedlings have already emerged, appropriate irrigation should be used to protect the seedlings during the period of low temperature and continuous rain.

It is expected that starting in mid-April, the cold air affecting China will weaken, and temperatures in the central and eastern regions will rise noticeably, so the "late spring cold snap" weather will improve. But this weather process has provided a practical lesson for all sectors of society, especially agricultural production. At present, nationwide, spring will continue for some time. Relevant management departments still need to accurately understand the characteristics and harm of "late spring cold snap" weather, and make preparations to respond to spring cooling weather, so as to strive to minimize the impact of adverse weather on agricultural production.