Abstract: Plastic film mulching is a major management strategy for agricultural water saving and yield-increasing in arid and semi-arid areas. However, long-term and high-intensity plastic film mulching has caused serious “white pollution” and thus is not sustainable. In this study, we investigated the effects of residual film pollution on soil physical characteristics and cotton root growth under simulated residual film accumulation and drought. We designed a soil column installation with two irrigation amounts \[1950 m³·hm^-2 (50% field water-holding capacity, moderate drought), 3900 m³·hm^-2 (100% field water-holding capacity, full irrigation)\] and four residual film levels (0, 160, 270, and 490 kg·hm^-2). The results showed that soil physical properties were mainly affected by residual film amount. With the increases of residual film amount, soil bulk density increased, while saturated water content, field water-holding capacity, capillary water-holding capacity, and total porosity decreased. The increased residual film amount inhibited the expansion of cotton root, decreased root biomass, root surface area, root volume, root length, and root diameter, as well as the proportion of cotton roots in the 0-20 cm soil layer. Except for field water-holding capacity, all the above mentioned indices showed significant differences when the residual film amount exceeded 270 kg·hm^-2. Under the same amount of residual film, root architecture of the high irrigation quota was better than that of the drought treatment. A comprehensive analysis showed that the increasing range in soil bulk density was 1.88%, while the decrease ranges in saturated water content, capillary water retention, and total porosity were 7.97%, 6.42%, and 9.39%, respectively. Root biomass, root surface area, root volume, and root diameter decreased by 41.34%, 64.10%, 47.27%, and 86.67%, respectively. In conclusion, residual film pollution severely damaged soil structure, inhibits root growth, and led to decreases in soil physical properties, root water and fertilizer absorption capacity. The reduction of such effect may require more water consumption, which will further exacerbate the water shortage crisis. Therefore, the corresponding residual threshold should be strictly controlled below 270 kg·hm^-2. The results provide theoretical support for the risk assessment and control strategy of farmland residual film pollution.

Key words: residual plastic film, cotton, root system, soil physical property.