Distribution and influencing factors of plastic film residues in topsoil of farmland in Gansu Province

The application of agricultural film mulching technology has greatly promoted the development of agriculture in arid and semi-arid areas. Gansu Province has a large amount film, large coverage area, and long coverage time for plastic film mulching on farmland. The residual plastic film produced by plastic film mulching is a prominent problem that affects the green and sustainable development of agriculture. In this study, the distribution and influencing factors of plastic film residue in the 0–30 cm soil of farmland were investigated by setting up 960 monitoring sample sites in the main areas with mulched farmland of Gansu Province, combined with sample collection and farmer survey methods. This study aimed to evaluate the current status of plastic film residue in farmlands and provide guidance for prevention and control measures of pollution of plastic film residues in Gansu Province. The results showed that the residual amount of plastic film was 0.02−204.75 kg·hm⁻², and the median of plastic film residues was 12.96 kg·hm^–2 in 960 sites. Most of the mild and moderate pollution sites were located in Hexi-irrigated agricultural areas. Among them, the proportion of plastic film residues was 97.6% at the clean threshold (less than 75 kg·hm⁻²), 1.8% at mild pollution threshold (75−120 kg·hm⁻²), 0.6% at moderate pollution threshold (120−270 kg·hm⁻²), and 0 at severe pollution threshold (higher than 270 kg·hm⁻²), respectively. The residual amount of plastic film was affected by the number of film mulching years, type of planting crops, type of planters, recycling methods, and other factors. The residual amount of plastic film with film mulching years of 11−20 years and >20 years was significantly higher than that with film mulching years of 6−10 years (P<0.05), and the longer the age, the greater the residue. The amount of residues of the seed crop site was the largest at nearly seven times that of the greenhouse vegetables site. Plastic film residues in the fields of seed crops, economic crops, maize, potato, outdoor vegetables, and Chinese herbal medicine were significantly higher than those in the fields of greenhouse vegetables (P<0.05). The residual amount of the cooperative field was 1.5 times that of the general farmers. The farmland residual film was recovered in three ways: manual picking up, manual picking up + mechanical recycling, and mechanical recycling. The amount of residual film in fields with the recovery method of manual picking up + mechanical recycling was significantly higher than that with manual picking up (P<0.0001). Type of planting crops was the dominant factor causing spatial changes in plastic film residues in the study area. After removal from the farmland, the residual film was regenerated and processed through merchants purchasing, networks recycling, or farmers’ exchanging. This survey of residual plastic films showed that the spatial distribution of plastic film residues in farmland soil was quite different in Gansu Province, and the residual plastic film in the topsoil of farmland was generally at a low level, showing the distribution of pollution at a few sites and overall cleanliness on the surface. Prevention and control of plastic film residues should be further carried out under the guidance of reduction, recovery, and substitution. This study provides data for further improvement of policies and mechanisms for the scientific use and recycling of plastic films in Gansu Province.