Plastics found in strawberry fields

Researchers have found that the plastic mulch used to support the growth of Californian strawberries sheds large quantities of plastic mulch fragments. These particles negatively impact soil qualities, casting doubt on the long-term viability of their use. The findings may apply worldwide to plastic use in agricultural production.

Presenting the work at the Goldschmidt geochemistry conference in Lyon, Ekta Tiwari from the Sistla group at California Polytechnic State University said a huge quantity of macroplastic material — particles bigger than 5 mm across — is being shed where mulch is used to enhance strawberry production.

Plastics, such as polyethylene, are used in agriculture, where they provide many benefits. Plastic mulch films are tucked around the base of the plant, which can help control weeds and pathogens, reduce water evaporation and prevent soil splashing on fruit.

The mulch is applied in rows and removed after the crop’s seasonal production is complete. But even careful land stewardship by farmers does not ensure all the plastic is removed because fragments get left behind and adhere to the soil during removal. The researchers observed the accumulation of plastic fragments within farm soils after decades of removal, looking for macroplastics.

After the seasonal removal of plastic film, the researchers found that the distribution of macroplastics was fairly uniform. On field surfaces, they found up to 213,500 macroplastic particles per hectare. This does not include subsurface particles, which were not surveyed. They are also currently analysing the same soil samples for microplastics.

Most of the particles were identified as polyethylene. In preliminary findings, the researchers found that as levels of macroplastic pollution increased, soil moisture content, microbial respiration and plant-available nitrogen declined.

“The plastic mulch provides benefits, but at the expense of long-term soil quality. It’s difficult and expensive to remove these particles from the soil, so once they are there they can stay there indefinitely,” Tiwari said.

There are alternatives to polyethylene mulches, such as biodegradable plastic mulches or natural mulches, but these come with an economic cost. The use of plastics in agriculture is also increasingly regulated, such as in the European Union.

Professor Sean Schaeffer from the Department of Biosystems Engineering & Soil Science, University of Tennessee, said plastics are vital to maintain agricultural production and are used to various purposes. Research on them is relatively recent, so studies are crucial to increasing understanding about the plastic problem.

Image credit: Seeta Sistla