Degradation of agricultural biodegradable plastics in the soil under laboratory conditions

Mulches, usually consisting of polyethylene films, are used in agriculture to improve production. The main drawback of using polyethylene is its extremely high stability. Removing it from the field is usually not feasible, and so wastes remain accumulating in the field and pollute the environment. As an alternative, five potentially biodegradable plastic films for mulching (maize thermoplastic starch-copolyester, cereal flour-copolyester, polylactic acid-copolyester, polyhydroxybutyrate, and potato thermoplastic starch-copolyester) were tested to evaluate their degradation in an agricultural soil. Polyethylene film was used as control. A soil burial test was carried out during 6 months under laboratory conditions and film weight loss, chemical changes and soil microbial activity were monitored. Weight loss was fastest for the polyhydroxybutyrate film, followed by potato thermoplastic starch-copolyester and cereal flour-copolyester. Maize thermoplastic starch-copolyester and polylactic acid-copolyester required 5-6 months to disintegrate. Concomitant to the weight loss, chemical changes in the films and an increase in soil microbial activity were noticed. From the disintegration and biodegradation results of the biodegradable tested films, it is concluded that these films are an alternative for avoiding the soil pollution drawbacks of the polyethylene mulching films.The authors are grateful to the Spanish Ministry of Science and Innovation, MICINN (Research Project AGL2008-03733/AGR) and the University of Lleida, Spain (Research Project UdL006197) for financial support