Dirt on the soil agricultural plastic pollution in the United States and China

Farmers in the United States and China who cultivate strawberries, melons, and other fruits and vegetables often face the same daunting challenge: after harvest, they must collect and dispose of the plastic mulch used to increase production. After months in the scorching sun, the plastic sheeting begins to shred and breakleaving fragments in the ground.

More … than 350 million tons of plastic are produced and consumed around the world every year, and the proportion of plastics that can be reused and disposed of safely and efficiently is very low—currently only about 9 percent plastic is recycled. Single-use plastics, like cups, utensils and food wrappers, take up most of the airtime as plastic waste pollution, but agricultural plastic polluting the ground is a neglected time bomb and an urgent global problem.

The march of plastic mulch

In the United States only, 126 million pounds of plastic mulch covers the soil to reduce weed growth, conserve water and warm the soil to extend the growing season, increasing yields by 30%. In an effort to identify land-based sources of plastic pollution in the ocean, Jazmine Mejia-Munóz from Monterey Bay National Marine Sanctuary and his team found that plastic covered California farmland used to grow more than half of America’s lettuce and celery and more than a quarter of other fresh fruits and vegetables.

The advantages of plastic sheeting in agriculture was demonstrated in the 1950s by Professor Emmert of the University of Kentucky. Known as the “father of agricultural plastic development”, he showed how plastic could be used for greenhouses, mulches and row covers. Plastic mulch was also developed in Asia by Japanese scientists in the 1950s and was used for tobacco production in the 1960s. The technology was introduced to China in the 1970s. The use of plastic mulch then spread beyond China and by 2000 it was widely used in the Philippines.

More plastic mulch is used in Asian agriculture than the rest of the world. China is now the largest user of plastic mulch film, which covers 10% of cultivated agricultural land in China, i.e. 18.4 million hectares, an area the size of the state of Nebraska.

For more 40 years Chinese farmers used plastic mulch to help grow fruits, vegetables, grains, peanuts, cotton and tobacco. However, the plastic they used was as thin as plastic wrap, only 4 to 8 microns—a zipper bag is 38 microns. The thin plastic tears easily, making it almost impossible to pick up, so the shredded plastic stays in the ground.

China’s 2011 plastic waste survey found an average of 34 kilograms of plastic residue polluted every hectare of agricultural land, the equivalent of more than 6,000 plastic grocery bags. According to Professor Yan Changrong of the Chinese Academy of Agricultural Sciences, the second national agricultural plastic survey of 2017 found that the average had risen to 52 kg/hectare. The greatest impact of what has been called a “white revolution” has been the use of plastic mulch with drip irrigation to grow cotton in the cold, dry areas of northwest China, nearly doubling the yield compared to the traditional cotton-growing areas of the Yangtze and Yellow River basins. . Today, the heaviest use of plastic is found in Xinjiang province in northwest China, where plastic pollution is 4 times higher than 200 kg/hectare (more than 36,000 bags of plastic groceries). The cost of collecting and recycling the mulch film at the end of the season is about 450 yuan ($70) per hectare if it can be collected.

Agricultural plastic pollution negates profits

According to Professor Yan, the direct economic benefit of plastic mulch is an increase in rural income estimated at 120-140 billion yuan per year (19-22 billion US dollars). Global consumption of plastic mulch is nearly 2 million tons per year, of which about 75% is used in China. Due to the intensive and continuous use of plastic mulch, the residual pollution of agricultural plastic films is uniquely Chinese.

At first, plastic shards accumulating in the floor were a nuisance, getting caught in equipment. For example, in northwest China, cotton farmers frequently have to shut down their equipment and clean up collected plastic fragments to apply the next plastic sheet when planting cottonseed, which increases processing time. planting and labor costs. Plastic fragments also cause harvesting problems. Plastic trapped in cotton bales reduces its quality and cannot meet high-end textile standards.

Research now shows that plastic damages soil structure, stunts plant development and alters the soil carbon cycle which affects greenhouse gas emissions. While plastic sheeting is often used to help farmers adapt to a drier climate, at least 9 studies in China have found that using plastic mulch increases greenhouse gas emissions of agriculture from 10 to 32%, aggravating the climate crisis. Emissions come from increased nitrogen oxides emitted from the soil, greenhouse gases emitted during the production of plastic, and the fuel to transport it and apply it to agricultural fields.

Plastic residues in the soil also reduce crop yield by 13% and water use efficiency by 7.8%. the greater abundance of plastic in agricultural soil is found in Xinjiang province, western China. Plastic mulch has been used continuously for over 20 years in this region and plastic pollution is now reducing crop yields by 19%.

China takes the lead in ending plastic soil pollution

While agricultural plastic pollution is significant, the use of agricultural plastic is largely unregulated. In the United States, some state and local governments limit the burning of plastic to control air pollution. Recycling programs for agricultural plastics started and failed, mainly because dirt is half the weight of plastic and dirt is damaging the recycler’s shredding equipment.

In December 2019, the Chinese Ministry of Ecology and Environment and National Development and Reform Commission (NDRC) has proposed new regulations to reduce the agricultural plastic problem. Regulations require the use of thicker, higher quality mulch that can be reused, collected and recycled. New plastic order ban of the NDRC prohibits the production and sale of the traditionally used thin mulch film of less than 10 microns. The order continues to promote the use of biodegradable mulch and improve recycling. The NDRC also supports pilot demonstrations on agricultural plastic waste recycling and treatment.

Agricultural plastics have brought so many benefits that their use is likely to continue, despite pollution concerns. In China, the use of plastic mulch is expected by 2025 to reach 2.28 million tons and cover an area of ​​23.4 million hectares. Research support is needed to foster the development of biodegradable mulch films and technologies to collect and remove plastic residue from soil and improve the reuse and recycling of plastic mulch. The impact of plastic soil residues on crop growth and soil health must be considered in developing policies related to sustainable agricultural development in the context of global climate change.

Karen Mancl is a professor of food, agricultural, and biological engineering at The Ohio State University and director of OSU’s Soil and Environmental Technology Learning Lab. She holds a doctorate in water resources from Iowa State University, a master’s degree in East Asian studies, and a master’s degree in public policy from The Ohio State University.

Sources: AGRIS, Agronomy for Sustainable Development, ATTRA, CGTN, Cornell Cooperative Extension, CORESTA, FAO, Florida Agricultural Plastics Recycling Cooperative, Journal of Cleaner Production, Journal of Environmental Biology, Monterey Bay National Marine Sanctuary, National Development and Reform Commission, National Geographic , Science Daily, Science of the Total Environment, Statista, University of Tennessee Extension, Waste Advantage, World Agriculture

Photo credit: strawberries covered in plastic mulchcourtesy of Barmalini/shutterstock.com.

Bryce K. Locke