Strawberry Fields Forever? Strawberry production leaves behind long-term plastic

Researchers have found that plastic mulch used to support growing California strawberries releases large amounts of plastic mulch debris. These particles have been shown to negatively impact soil quality, raising doubts about the long-term viability of their use. The findings from the survey likely apply worldwide to the use of plastics in agricultural production.

Presented their work at the Goldschmidt geochemistry conference in Lyon, Postdoctoral researcher Dr Ekta Tiwari (of the Sistla group at California Polytechnic State University) said “What we saw was large amounts of macroplastic material – particles larger than 5 mm – being shed where the mulch was used to increase strawberry production. These can remain in the ground for decades or more”.

Plastics, such as polyethylene, are increasingly being used in agriculture, for example in poly tunnels. Plastic mulch films are widely used in agriculture, where they provide a variety of benefits. They are tucked around the base of the plant, which can help control weeds and pathogens, reduce water evaporation, and prevent soil splashing on the fruit (which is especially important for strawberries).

Mulch is applied in rows and then removed once the crop’s seasonal production is over. However, even careful land management by farmers does not ensure that all the plastic is removed as fragments are left behind and stuck to the soil during removal. After decades of annual plastic mulch application and removal, researchers observed an accumulation of plastic debris in agricultural soils, even in very well-managed fields. Researchers are looking macroplasticwhich are pieces of plastic with a diameter greater than 5 mm.

Ekta Tiwari carry on “We conducted a systematic survey of the strawberry fields after the plastic film was seasonally removed. We find that the distribution is quite uniform. On the field surface alone, we found up to 213,500 macroplastic particles per hectare. That doesn’t include subsurface particles, which we don’t survey. In addition, we are currently analyzing soil samples for the same microplastics, which are smaller particles, less than 5 mm; this has not been included in our findings”.

Note: One hectare is 10,000 square meters. For comparison, the average professional soccer field is about 7100 square meters.

Most of the particles are polyethylene (identified using Fourier transform infrared spectroscopy). In their initial findings, the researchers found that as levels of macroplastic pollution increased, soil water content, microbial respiration, and nitrogen available to plants decreased.

Dr Tiwari added “Plastic mulch provides benefits, but at the expense of long-term soil quality. It is difficult and expensive to remove these particles from the soil, so once they are there, they can stay there forever”.

We tend to think of strawberries only to be enjoyed, but this goes to show that even something as delicious as fresh strawberries can be detrimental to the environment. We are working with manufacturers to see if we can reduce these costs”.

There are alternatives to using polyethylene mulch, such as biodegradable plastic mulch, or natural mulch such as straw, but these options are cost effective. However, the use of plastics in agriculture is also increasingly regulated, see for example EU information at https://environment.ec.europa.eu/system/files/2021-09/Agricultural%20Plastics%20Final%20Report.pdf

Commenting, Professor Sean Schaeffer (Department of Biosystems Engineering & Soil Science, University of Tennessee, USA) said:

“Pplastics, and plastic mulches in particular, are critical to sustaining agricultural production. They are used for a variety of purposes including soil moisture retention, soil heating/cooling, as well as weed or pest control. The use of agricultural plastics is increasing worldwide, with California being the largest user of agricultural plastics in the US. Research on the fate and transport of plastics in soil and water systems is relatively new, so research like this is critical to increasing our understanding of the scope of the plastics problem. We currently know very little about the distribution, size and type of plastics in soils in the largest states, both in land area and in agricultural production.”

This is an independent comment, Professor Schaeffer was not involved in this work.

This work is ongoing and has not been peer reviewed. Researchers are currently evaluating the levels of microplastic pollution (particles smaller than 5 mm) left by plastic mulch. This study provides a baseline for understanding the extent of plastic pollution in the US agricultural system and can help improve land management practices by assessing the biogeochemical consequences of plastic accumulation in agricultural soils.

The Goldschmidt Conference is the world’s premier geochemistry conference. This is a joint congress of the European Geochemical Association and the Geochemical Society (USA). It takes place in Lyon, France, from July 9-14. Nearly 5000 delegates are expected to attend. https://conf.goldschmidt.info/goldschmidt/2023/goldschmidt/2023/meetingapp.cgi

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