"Look, the mulch under the soil is gone, and there is still a little mulch left outside, and it will shatter when you pinch it."
During the summer time, in the farmland of Changzhou City, Jiangsu Province, Cai Dongsheng, chairman of the Changyu Red Taro Professional Cooperative, happily told reporters while turning the soil with a hoe.
The picture shows that in June this year, the paddy field of Jiangsu (Kunshan) Modern Agriculture (Rice and Wheat) Science and Technology Comprehensive Demonstration Base used straw degradable plastic film.
"Our cooperative has planted more than 5,000 mu of red taro. In July of last year, it was time to hire someone to remove the mulch manually. It took at least 4 working hours per mu, which is about 320 yuan. Covered with a layer of soil." Cai Dongsheng said with emotion, "This year, the new biodegradable mulch film developed by the Jiangsu Academy of Agricultural Sciences is used, and there is no need to manually remove the film, and there is no need to worry about 'white pollution'."
Not only the red taro in Changzhou, but now, tomatoes, garlic and sweet potatoes in Jiangsu, as well as potatoes in Ningxia, and melons in Hainan... all use this biodegradable plastic film.
Modified straw and polymer materials "hand in hand"
Mulch was once called the "white revolution" of agricultural production. In the 1970s, the plastic film covering technology was introduced into China, and then it was rapidly popularized. At present, the annual consumption of agricultural plastic film in my country has reached 1.4 million tons.
The large-scale use of plastic mulch film not only helps farmers increase production, but also brings about "white pollution" that is difficult to degrade. Broken mulch will also be converted into microplastics, which enter the human body through animals and plants, endangering people's health. Although some degradable plastic film products have been launched in the international market, their high cost and single performance make it difficult for Chinese farmers to accept them.
On the other hand, with the comprehensive introduction of the "burning ban", the comprehensive utilization of straw has become a new problem.
"Can we find a way for efficient utilization of straw, and at the same time reduce the cost of degradable plastic film?" In 2011, Xu Lei, who graduated from Soochow University with a major in polymer materials, came to Jiangsu Academy of Agricultural Sciences. With the vision of interdisciplinary integration, he is keenly aware that this is a new field with huge demand.
Xu Lei, looking for the direction, plunged into the laboratory. However, the first problem stumped him: rough straw and polymer materials "can't play together" at all.
"The main component of degradable mulch film is PBAT (degradable resin), while the main components of straw are cellulose and lignin. Straw has strong intramolecular hydrogen bonds, which makes it less compatible and dispersable with degradable resin. It's not good." Xu Lei said, this is like milk powder brewed in cold water, with large and small "milk bumps" floating on the surface, which cannot meet the film-forming conditions.
In order to fuse the two, Xu Lei used a stronger grinder to grind it again and again. The diameter of straw particles has been reduced from 300 mesh to 500-800 mesh, which is barely usable, but the energy consumption cost has also greatly increased. Xu Lei was confused.
In 2019, he went to a straw feed factory in Taicang, Jiangsu for investigation, and overheard the person in charge complaining: the dust generated by cutting straw is 100 tons per month, and it is really annoying that it cannot be used and the grinding head is blocked.
Xu Lei's eyes lit up immediately and asked, "What is the particle size of this dust?"
"About 1,000 meshes. What's wrong?" The person in charge of the feed factory looked at him puzzled.
"That's great! I'm just looking for it." For a moment, Xu Lei was overjoyed.
However, the surface activity of 1000 mesh straw particles is still not strong, so we must find a way to make the straw particles more "lively".
"We have tried many ways, and finally found a modification method, the principle of which is like adding an 'activating layer' to the surface of straw particles, that is, using modification treatment technology and straw-plastic blending granulation process, the straw powder and the Biodegradable polymers are fully combined, and straw-plastic composite biodegradable materials are made through molding technology." Xu Lei said.
Personalized mulching film "tailored" for crops
At the beginning of 2020, with the unremitting efforts of Xu Lei's team, the new biodegradable mulch film was finally successfully developed, and the promotion and application volume reached 300 tons that year.
This year, Cai Dongsheng and the others adopted this new type of biodegradable mulch film with the idea of "try it out". The film that was covered before the Qingming Festival disappeared in mid-July.
"Under the specific environment of the field soil, the plastic film can be degraded within a certain period of time through the action of microorganisms, and finally return to nature as water and carbon dioxide." Xu Lei said.
In the new type of plastic film, straw powder accounts for 30%, which not only greatly reduces the cost, but also strengthens the mechanical properties. Its "toughness" is much higher than that of other biodegradable plastic films, and the tensile strength and thermal insulation performance of the product can be simultaneously improved.
With the promotion of the new type of plastic film, the problem of adaptability has become prominent again - my country is a vast territory, cotton in Xinjiang needs to resist ultraviolet radiation, tobacco in Guangdong needs to irradiate the roots of sunlight, and potatoes in Ningxia have higher requirements for thermal insulation and moisture retention...
"The climate characteristics, soil moisture and the needs of crops are different in different regions. It is difficult for a single formula and function of degradable mulch to match the growth needs of different crops." Xu Lei said, this is like wearing the same clothes, which cannot meet the different needs of people in different regions. seasonal needs.
Is it possible to develop personalized mulch film for different regions and different crops, so that mulch film can play a better role in increasing the yield and quality of crops?
The picture shows that the degradable plastic film has achieved good results in the production and application of sweet potato in Jiangsu.
In 2020, Xu Lei tried to develop a special degradable plastic film suitable for sweet potato cultivation in Jiangsu. This mulch film is based on straw powder mixed with degradable resin, and superimposed foam material is used as a thermal insulation layer. Field tests show that the yield of sweet potato using the new mulch film increases by about 10% compared with the traditional PE (polyethylene) mulch film, and the commercialization rate increases by about 12%.
"This year, we have successfully developed a multi-layer biodegradable film. The outer layer is straw particles, the middle is degradable resin, and the inner layer is wormwood." Xu Lei said that such a film can not only resist the sun's ultraviolet radiation, but also achieve Biological repellent, reducing pesticide usage.
Through experiments, Xu Lei's team established a degradable plastic film design model suitable for different scenarios, incorporating parameters such as climate, soil, cultivation method, and growth cycle.
"After the model is established, as the amount of data continues to increase, specific parameters can be input to generate the exclusive mulching film formula and processing technology. Later adjustments can be made according to the growth conditions of local crops." Xu Lei said that at present, they have developed personalized The mulch film has at most 5 layers of composite functional film, which can be "tailored" for a variety of crops.
From "white pollution" to "green revolution", the interdisciplinary integration has turned waste into treasure, not only connecting an agricultural circular economy industrial chain, but also contributing scientific and technological strength to improving the agricultural ecological environment and building beautiful countryside.
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