Spatial-temporal distribution and accumulation characteristics of residual plastic film in cotton fields in arid oasis area and the effects on soil salt transport and crop growth

Abstract

Plastic film residue pollutes farmland ecosystems and the natural environment though the plastic film employed in drip irrigation increases the utilization coefficient of irrigation water efficiency. Extensive studies have been conducted on soil pollution arising from residual films in northwest China, whereas the limits of the positive effect of plastic films on crop growth and the negative effect of residual plastic films remains unclear. To investigate the effects of residual films on soil salt transport and crop growth, the soil was collected from cotton fields under long-term film mulching and drip irrigation in arid oasis areas in this study to determine the distribution and accumulation of residual plastic films in the soil layers of an agricultural ecosystem. A plot experiment with eight residual film densities was performed in a cotton field at the experimental station, given the correlation between the film mulching year and residual film density. The effects of the residual film on soil salt migration and crop growth were elucidated through the observation of soil and cotton growth indicators, biomass, and yield. As indicated by the results, the density of residual mulching film in cotton fields under continuous mulching for five years exceeded the limit value of the determination standard (75 kg/ha). With the increase of the film mulching years, the residual film accumulated at a rate of 15.0 kg/ha annually, and it tended to migrate to the deep soil each year. The amount of the residual film of size < 4 cm2 was risen markedly, resulting in a problem of increasing fragmentation. Notably, the amount of the residual film was positively correlated with the variability in soil salinity. The growth index, biomass, and yield tended to be decreased with the increase of the mulching years. The yield reduction rate attributed to the residual film exceeded the yield increase arising from film mulching at the residual film density of 1210 kg·ha−1. This study takes on a critical significance to increasing the recycling efficiency of the residual films and ensure sustainable agricultural development in an oasis.