Plastic Mulch Improves Plant Growth For One Season, Then Damages Soil: Study

China has led the world in using plastic-film mulch to increase the productivity of its crops, and now it needs to lead the world in removing the plastic residue damaging its croplands, according to a study out this week.
Just days earlier, as if on cue, the Chinese government released Friday the draft of a law that would ban the use of very thin plastic film mulch.
“We found that the use of plastic mulch can indeed increase crop yields on average by 25%–42% in the immediate season due to the increase of soil temperature (+8%) and moisture (+17%),” according to the meta-study published April 12 in Global Change Biology. “However, the unabated accumulation of film residues in the field negatively impacts its physicochemical properties linked to healthy soil and threatens food production in the long term.”
Plastic film is often seen in the United States on strawberry fields. But China has led the world in using it, particularly in arid regions, with increased crop production in the first year and wealthier farmers as a result.
But the same plastic now threatens that productivity and wealth, according to the study led by scientists from the Chinese Academy of Agricultural Sciences and the University of Melbourne.
The meta-analysis incorporates the results of 110 peer-reviewed studies and concludeds that residues from plastic mulch damage crop yield, plant height, root weight, and soil properties including soil water-evaporation capacity, soil water-infiltration rate, soil organic matter and soil available phosphorus.
China has an estimated 550,800 tons of plastic residue lingering in its croplands from plastic films that were not fully recovered.
“These physical soil changes help to explain the reduction in root weight, which in turn affect the nutrient uptake of crops and ultimately, result in the reduction of crop yield,” the authors write.
The short-term benefits of plastic film mulch are so dramatic, the authors concede, that the question is not whether the use of film should be stopped, although they recommend the use of thicker films and biodegradable films.
“Instead, the focus should be on mitigation strategies targeted at recovery of plastic film after use,” they write.
“China's story also sounds the alarm for the use of plastic film in other developing countries—that is, the recovery of plastic film or use of biodegradable plastic film is essential for protecting our croplands.”

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