By Karen Mancl
Surprisingly, 90% of the world’s plastic greenhouses are in China, covering 8 million acres, about the area of Maryland. Using greenhouses doubles yield and extends the growing season, so farmers are able to produce more food on less land. The thick plastic greenhouse sheeting, however, does not work forever. Long exposure to UV light starts to break down the plastic. After 3 years it needs to be replaced. So, what happens to all that waste?
In addition, agricultural plastic mulch use started in the 1980s. China is the world’s largest user of plastic film mulch as well. Current use in China is over 2 million tons of plastic covering 77,200 square miles, like covering every inch of Nebraska with plastic mulch. The mulch blocks weed growth, reducing the need for herbicides and protecting the soil from erosion. The plastic also helps warm the soil and conserve water. The benefits of plastic mulch are significant, increasing yield and water use efficiency by about 25%, and benefitting farming in areas that would otherwise be too dry or cold to grow food. Growing crops under plastic has a dark side, however. It is dirty, hard to recycle, and generates a mountain of plastic waste.
Mulch is much too thin
The plastic mulch used in China is as thin as plastic wrap, only 4 to 8 microns – a zip lock bag is 38 microns. The thin plastic easily tears, so it is only used for one growing season and is almost impossible to pick up. The thin mulch shreds and flakes, and balls of plastic stay in the soil or are washed away into streams that lead to the ocean. Flakes of plastic caught up in animal feed are ingested by livestock.
The plastic left in the soil is changing the soil environment. At first, the remnants in the soil were a nuisance, clogging farm equipment, blowing in the wind, getting caught on fencing and washing into ditches. Now, more than 20 years of plastic building up in the soil has started to interfere with roots and water movement, reducing crop yield and canceling out some of the benefits of the plastic mulch.
U.S. agricultural plastic is booming
China is not alone in dealing with agricultural plastic waste, U.S. farmers also use plastic, generating 816 million pounds of plastic waste annually. U.S. farmers use 126 million pounds of plastic mulch and 422 million pounds of plastic containers. In addition, plastic irrigation tubing, feed bags, and greenhouse plastic add to the growing volume of waste. One third of the agricultural plastics in this country are used in Florida. In the United States, farmers use thicker and stronger plastic mulch, from 15 to 50 microns. While the weight and cost increases with thickness, the thicker film can be picked up and reapplied so it can be used for at least 2 years. Getting the plastic out of the field is the first step to reuse, recycling, or safe disposal.
Soil, stuck to the plastic mulch makes up half of the plastic’s weight. The dirt damages the recycler’s shredding machines, making it difficult to recycle. Plastic that is too dirty for recycling is piled up and burned in the field.
Right now, the United States has no policies to require or encourage recycling agricultural plastics. Programs are voluntary and limited by market demand for recycled plastic. However, some farmers are finding ways to collect and recycle plastics used in agriculture. Plastic irrigation tubing is relatively clean and easy to collect. A California plastic irrigation tubing producer is closing the circle and now collects used tubing. After it is shredded, washed, and pelletized, it is made into new tubing.
The Missouri Botanical Gardens in St. Louis collects and recycles plastic flowerpots, trays, and cell packs from landscapers and home gardeners. Each year they keep 350,000 pounds of plastic out of the landfill.
Since 1992, the Agricultural Container Recycling Council has coordinated recycling of chemical containers across the United States. In 28 years, the Council has recycled 200 million pounds of pesticide jugs and drums keeping them from filling up hazardous waste landfills. The high-density polyethylene (HDPE) is recycled into agricultural drainage tile, fence posts, pallets, and nursery pots.
Plastic mulch remains the biggest recycling challenge, because it is wet and dirty. Recycling programs throughout the United States come and go. The few programs to help farmers, like those in New York and Florida, collect the mulch but have struggled to find a market for the plastic. Gene Jones of the Florida Agricultural Plastics Recycling Cooperative emailed “At this time, not much is moving with regard to ag plastics especially mulch film. We do have some market for drip tape and cleaner greenhouse films but that is about it.”
China tackles agricultural plastic pollution
In December 2019, Chinese Ministry of Ecology and Environment and the National Development and Reform Commission proposed new regulations to reduce the agricultural plastic problem. China has new regulations that require the use of higher quality, thicker mulch that can be reused, collected, and recycled. Right now, of the 2 million tons of plastic mulch used in China, only 180,000 tons is being recycled. In 2018, China stopped importing plastic waste from foreign countries and is prioritizing domestic recycling.
Agricultural plastics have transformed agriculture and the lives of farmers. It is unlikely that the use of plastics will be abandoned. Research is underway to develop biodegradable agricultural products. Ohio State University, for example, is developing plant-based plastics that degrade in 45 days. Chinese scientists are also developing plant-based plastics, but right now but they are still too expensive for widespread use. The current focus is on improving the ability to gather, reuse, recycle, and safely dispose of agricultural plastics.
Karen Mancl is a Professor in the Ohio State University Department of Food, Agricultural & Biological Engineering. This column is provided by the OSU Department of Food, Agricultural and Biological Engineering, OSU Extension, Ohio Agricultural Research & Development Center, and the College of Food, Agricultural and Environmental Sciences. For more information, Mancl can be reached at 614-292-4505 or Mancl.firstname.lastname@example.org.