Before the spring sowing of crops and after the autumn harvest, there is often a spectacular scene in China's rural areas: the whole family stoops down to the fields to pick out the plastic film left in the soil. Because of its function of heat preservation and moisture retention, transparent plastic mulching film on crops can increase production and income, but it brings a flood of white pollution.
In 1979, China introduced plastic film mulching cultivation technology from Japan, which can effectively achieve agricultural production and efficiency increase. Therefore, plastic film has been widely used in China. At present, plastic film is the fourth largest pesticide production material in China after pesticide, chemical fertilizer and seed. According to relevant data statistics, in 2017, the amount of plastic film used in China was 1.437 million tons, and it is predicted that the area covered by plastic film will reach 2020 It reaches 305 million mu, and the annual consumption is 1.993 million tons. In 2025, the area covered by plastic film will reach 351 million mu, and the consumption will reach 2.279 million tons.
There are four kinds of general effects of plastic film, namely, heat preservation, moisture retention, fertilizer retention and weeding. The plastic film has black membrane, white membrane and double sided membrane. The double side membrane is silver film or white film, and the other side is black film. Silver film can reflect light and prevent aphids. It is suitable for planting melon and fruit crops. In addition, there are special weeding film. The use of special weeding film can reduce the growth of weeds and avoid being cut by sharp leaves such as sugarcane. The use of agricultural plastic film can effectively control the temperature and humidity of soil, reduce the loss of water and nutrients, promote the high or stable yield of crops, and increase the efficiency of agricultural production.
But at the same time, due to the one-time use of plastic film, there will be a large number of residual film left in the soil every year. However, plastic mulching films are mostly polyethylene with molecular weight of tens of thousands to hundreds of thousands, which are difficult to degrade in nature. The residue of plastic film is buried in the soil. Once the seeds are wrapped and twisted after sowing, the roots can not be rooted down, and the seedlings will die. These plastic film fragments can form a barrier layer in the soil, so that the flow of water, gas and fertilizer in the soil is blocked, resulting in soil structure hardening, seriously harming the ecological environment and causing white pollution. Statistics show that the average plastic film residue in Hanyuan area of Northwest China is 7 kg / mu, and that in serious places is more than 15 kg / mu. It has become an urgent task to solve the problem of soil polluted by plastic film mulching.
In order to study the application effect of degradable plastic film on farmland and explore a new way to control farmland film pollution, from 2015 to 2017, the agricultural ecology and resources protection general station of the Ministry of agriculture and rural areas and the Institute of agricultural environment and sustainable development of Chinese Academy of Agricultural Sciences carried out comparative experiments of degradable plastic film in 34 experimental sites in 13 provinces (autonomous regions and cities) in China, covering the Northeast sandy area, southwest mountain area and North China There are five main plastic film mulching zones in plain area, northwest dry tableland area and northwest oasis area. The selected areas are rich in agricultural climate types and evenly distributed, and have strong representativeness. Six kinds of major plastic film mulching crops, such as corn, peanut, potato, cotton, tobacco and vegetables, were involved in the experiment. The test materials were from two categories of degradable plastic film products produced by 27 Enterprises: one was full biodegradable plastic film, which was blown with polyester or carbon dioxide epoxide and other biodegradable resin as the main components, a total of 20 companies; the second type was oxidation degradation film (also known as oxidation degradation film) It is blown by adding oxidant which can initiate and promote oxidation reaction on the basis of PE plastics, with a total of 7 companies.
From the test results, the main raw material of oxidative degradation film is polyethylene, and the final cracking component is still polyethylene. There is a secondary pollution problem. The performance of the film is not different from that of ordinary PE film. However, the degradation performance is not stable, and the problem of "white pollution" cannot be solved. After the introduction of the new national standard, the use price of oxidative degradation mulching film will be lower than that of ordinary PE film, which has a great market competitive advantage, but there is a greater environmental risk, so it should be promoted carefully.
All biodegradable plastic film can be completely degraded. It is made of biodegradable materials by secondary polymerization and modification. It can be completely decomposed by bacteria and microorganisms in 1-2 plant growth cycles, and finally form carbon dioxide and water, which has no harm to soil and crops, and completely solves the pollution of traditional plastic film on soil. The film has good performance on some crops, and has good economic benefits, which can be demonstrated and popularized in a large area. The whole biological degradation agricultural film technology has been developed as early as 2007. At present, the film is still in the initial experimental stage. At present, the cost per mu is as high as 160-200 yuan, which is 3-4 times of the conventional plastic film. It is difficult to completely replace the ordinary PE film in a short time. At present, the biodegradable plastic film of our company is in the stage of mass production, but a lot of experiments and data collection are needed for Hainan local climate.
