[Smart Farmers] When spring ploughing encounters "late spring cold", scientific prevention and control is indispensable

In early spring, in March, the temperature gradually rises across the country, and people can't wait to take off their heavy winter clothes and put on spring clothes. But sometimes, just when we feel the warmth, the cold air arrives unexpectedly. At this time, we often call it "late spring cold". The Central Meteorological Observatory predicts that the "late spring cold" will hit most areas in northern China in March, with local temperatures dropping by 10℃. So, what impact will the large-scale temperature drop in various places have on my country's agriculture, and how can the "late spring cold" be prevented and remedied?

What is “ late spring cold ”?

Can every temperature drop in spring be called a "late spring cold"? Actually not. According to the national standard "Meteorological Indicators for Late Spring Cold", a late spring cold refers to a phenomenon in which the weather is warm in the early spring and cold in the late spring (March to May) every year, and the temperature in the late spring is significantly lower than that in normal years. Therefore, if the temperature drop is small and lasts for a short time during a certain cooling process, the cooling process will not meet the "late spring cold" standard and will have little impact on agriculture. Due to differences in geographical location, latitude, altitude, etc., the time when "late spring cold" occurs in different places varies. Generally speaking, the south warms up quickly, enters spring early, and the time of occurrence is early, while it is later in the north.

Description of late spring cold in ancient poems

What impact does “ late spring cold ” have on agriculture ?

Late spring cold weather is extremely unfavorable to agricultural production. For example, two severe late spring cold weather events in Yunnan Province in March 2011 caused agricultural economic losses of 283.678 million yuan in 18 counties (cities and districts) and a crop-affected area of ​​51,677.5 hm²; in 2021, a sudden late spring cold weather event hit the apple producing areas in the northwest, causing heavy losses.

Late spring cold mainly affects my country's agricultural crops such as rice, wheat, fruit trees, rapeseed, cotton, etc. If late spring cold occurs early, crops have not yet started to grow green, and frost damage can be remedied in time. The later the late spring cold occurs, the more impact it will cause on crops during their vigorous growth period, thereby reducing crop yields.

"Late spring cold" is the main disastrous weather during the early rice sowing and seedling raising period in the south, and is also the main cause of early rice seed rot and seedling rot. Rice is a warm-loving crop. If there is rainy weather with an average temperature below 12°C for several consecutive days during the sowing period, the rice seeds and rice seedlings will rot. In this case, farmers have to delay sowing, which affects the rice farming rules and further affects the normal growth and ear formation of rice.

"Late spring cold" will also aggravate wheat diseases and pests, affecting wheat yield and quality. When "late spring cold" occurs, the greater the temperature drop, the longer it lasts, and the lower the soil moisture content, the greater the damage to wheat. For areas where winter wheat is planted in advance, since more effective accumulated temperature has been obtained, the early spring enters the greening and jointing period in advance. When "late spring cold" occurs, the plants are less resistant to low temperatures and are prone to more serious disasters; for areas where sowing is late, the wheat seedlings grow weakly before wintering and have poor ability to resist low temperatures, so the impact of "late spring cold" is also more serious. Farmers should sow at the right time according to local temperature conditions and variety characteristics, increase the rate of strong seedlings in wheat fields during the wintering period, and reduce the impact of "late spring cold" on winter wheat.

The impact of "late spring cold" on fruit trees is mainly frostbite the flower buds, affecting pollination and fertilization, causing a large number of flowers to fail to develop normally and form fruits, or even a total loss of production; for young fruit trees, "late spring cold" directly freezes the seedlings, ultimately leading to poor development of the trees.

In addition, "late spring cold" often causes seeds to rot and seedlings to die for already-sown warm-loving crops such as cotton and peanuts.

Late spring cold weather hits winter wheat

How does agricultural production deal with “ late spring cold ”?

So how should farmers and relevant departments deal with the "late spring cold"? "Prevention" and "rescue" are two important aspects.

Pre-disaster prevention mainly includes four aspects: strengthening emergency management, monitoring and early warning, scientific prevention and control, and precise guidance.

Strengthen emergency management: We must establish and improve disaster prevention organizations, coordinate disaster prevention resources, strengthen joint prevention and control with relevant departments, implement preparations, and improve emergency management capabilities. We must further improve emergency plans to ensure that we are ready to respond to late spring cold weather at any time, establish and improve emergency plans such as disaster prevention and mitigation, clarify management responsibilities, work steps and effective measures, and improve emergency response capabilities and levels.

Monitoring and early warning: Strengthen communication and consultation with meteorological departments, pay close attention to weather changes, and release temperature drop information in a timely manner. Strengthen the training of meteorological forecasters to improve the timeliness, accuracy and practicality of forecasts. Strengthen disaster risk analysis, convey meteorological warning information to the public in a timely manner, and improve disaster prevention capabilities.

Scientific prevention and control: In the northern winter wheat area, before the arrival of late spring cold, the wheat fields with low soil moisture content should be irrigated or sprinkled to improve the field microclimate of the wheat fields and increase the temperature near the ground and leaves, which can play a certain role in preventing and mitigating the late spring cold. Antifreeze or potassium dihydrogen phosphate, brassinolide, seaweed, amino acids and other protective agents can also be sprayed on the leaves to prevent and mitigate the frost damage caused by late spring cold. The southern region should strengthen the management of rice seedling fields. Before the arrival of cooling and strong convective weather, the early rice seedling greenhouse film should be reinforced. Areas with conditions can cover double films to keep warm and protect seedlings; at the same time, before the temperature drops, appropriate spraying of phosphate fertilizers can enhance the resistance of rice seedlings and prevent cold air from causing rice seeds and seedlings to rot. Strengthen the management of rapeseed fields, spray boron fertilizers and phosphorus and potassium fertilizers in time to improve resistance. Waterlogged fields should be drained and waterlogged in time. Implement anti-freeze measures for open-field vegetables and fruit trees in advance. Among them, the traditional method of "starting a fire to create smoke" is still a common and quick and effective way to prevent frost and drive away cold in orchards.

Grapevines in the eastern foothills of Helan Mountain in Ningxia start fires to create smoke to prevent freezing and drive away the cold

Precise guidance: Guide the society to defend against meteorological disasters, take preventive measures, and effectively avoid the losses caused by meteorological disasters. Formulate and improve the technical plan for field management to prevent late spring cold as soon as possible, and make full use of radio, television, newspapers, mobile phones, the Internet and other media to publicize measures to prevent low temperature and freezing damage. Organize cadres and technical personnel to go deep into the fields, strengthen classified guidance, and help farmers implement key measures for anti-freeze and cold resistance according to local conditions and time. Ensure that services are provided to households and measures are implemented in the fields. Strengthen the adjustment and transportation of production materials such as disaster relief seeds (seedlings), fertilizers, and pesticides to ensure the demand for disaster relief materials.

Post-disaster relief includes two aspects: scientific agricultural post-disaster relief and strengthening the agricultural insurance system.

Scientific agricultural post-disaster relief: Take practical and effective disaster relief measures, such as drainage and ditch clearing, vegetation restoration, and pest and disease control, to effectively resist the occurrence and development of meteorological disasters. After the late spring cold, seize the "cold tail and warm head" weather to sow seedlings or transplant in the field; for severely affected fields, timely reseeding or replanting other crops, especially for those with rotten seeds and rotten buds in the seedling shed, timely reseeding or reseeding; timely topdressing once thin fertilizer, or spraying potassium dihydrogen phosphate and other foliar fertilizers to promote the plants to resume growth as soon as possible; timely clean the fields, strengthen disease prevention and control, avoid the aggravation and spread of diseases; strengthen daily management to promote the healthy growth of plants. For example, on April 10, 2020, Wuxuan County, Laibin City, Guangxi, immediately took remedial measures such as reseeding and fertilization after the late spring cold, which greatly reduced the harm caused by the late spring cold.

Strengthen the agricultural insurance system: Establish and improve the agricultural insurance system so that farmers can receive adequate economic compensation when they suffer from meteorological disasters, thereby reducing economic losses.

Produced by: Popular Science in China to Benefit Farmers

Producer: Guangming Online

Author: Zhao Jinyuan (graduate student of College of Resources and Environment, China Agricultural University)

Scientific review: Hu Qi (Senior laboratory technician and master's supervisor at the College of Resources and Environment, China Agricultural University)

Planning: Tu Ziyi