The use of plastics in agriculture has increased to an estimated 2.5 million tons annually over the past 70 years. Plastics in agriculture have many benefits, with plastic mulch films, for example, providing weed and pest control, soil moisture conservation, soil and air temperature control, and enhanced nutrient uptake. These benefits translate to an increase in yield, with a study showing that without the use of mulch film, China would need an additional 3.9 million hectares of arable land to produce the same amount of food.
However, plastics in agriculture are also harmful in many ways. To take plastic mulch films as an example again, their incomplete collection after use leads to accumulation of macro-, micro-, and nanoplastics on soil and other receiving environments. Typically composed of LDPE, these films also have chemical additives that can leach out after repeated applications, leading to harm to soil productivity and health.
An international team of scientists has reviewed the current applications and adverse effects of plastics in agriculture and suggested six ways to increase their sustainable use. Their focus areas are: collection and recycling; biodegradability; use of environmentally benign additives; education; renewable energy; and regulatory frameworks and incentives.
Regarding the first two, the scientists argue that two criteria should be added to the ‘3 Rs’ rule in determining sustainable use strategies and identifying after-use treatment options for plastics in agriculture: collectability after use, and duration of plastic use. The team claims that for applications that allow complete collection after use, reuse, and recycling should be the preferred treatment options, irrespective of the usage duration.
“For these applications, advances toward sustainability must be made by using plastics that do not chemically weather and fragment, and by implementing technologies that ensure complete collection after use, especially for plastics used below ground level, such as irrigation pipes,” they wrote.
To boost recycling rates of non-reusable soiled products in an economically feasible way, the academics suggest collecting bale wrap films, which are typically less soiled compared to ground-collected mulch films, and using pyrolysis to recycle mulch films. The team also stressed that it is crucial to develop effective techniques for removing soil and plant residues from plastic films, whilst suggesting that processes should be implemented on-site to reduce transportation costs.
For applications where plastics cannot be completed after use, of where they are too degraded or soiled to be reused or recycled, biodegradable plastics should replace conventional polymers, according to the scientists.
“The biodegradable plastics must be able to function throughout the entire period of application and, at the same time, be completely converted to CO2 and microbial biomass in the soil within a specified time period, at the end of their life,” they added. “These applications include, but are not limited to seed coatings, slow-release fertilizers, thin mulch films, as well as geotextile.”
The team shared their findings in “Plastics can be used more sustainably in agriculture,” recently published in communications earth & environment.