Effects of plastic film residue on cotton yield and soil physical and chemical properties in Xinjiang

Abstract: Background: Xinjiang is currently one of China's three largest cotton-planting regions. Cotton plantations account for more than half of the total agricultural area in Xinjiang. All cotton plantations in Xinjiang involve film mulching. However, this leaves behind plastic film residue, which has become a very serious problem. The average residual percentage is 24%, allowing plastic film residue to seriously harm soil quality and cotton yield. At present, because cotton yield has been improved, little attention has been paid to the hazards of plastic film residue. Purpose: The paper analyzed the effects of plastic film residue accumulation on soil quality and cotton yield by setting a density gradient. The paper studied the trends in and reasons for yield variation. Differences between cotton varieties with different root depths were compared. Method: On the basis of the complete survey of plastic film residue in the production area of short-staple cotton in northern Xinjiang, 6 density plastic film residue gradients were vetted based on the number of continuous years of film mulching: 0 (0 years), 250 kg/hm2 (13 years), 500 kg/hm2 (31 years), 1000 kg/hm2 (68 years), 1500 kg/hm2 (104 years), and 2000 kg/hm2 (141 years). The weight ratio of plastic film residues of 0-25, 25-100, and 100-200 cm2 was 1:1:1, and the films were mixed into the soil at a uniform depth of 0-40 cm. Cotton varieties included "Xinluzao 33" (deep root system) and "Xinluzao 13" (shallow root system). The area of each plot was 10 m2 and each gradient was evaluated three times. Yield-related traits and the physiochemical characteristics of the soil were studied. Conclusion: The density of plastic film residue can reach 1000 kg/hm2 after 68 years of continuous film mulching, and the cotton yield of "Xinluzao 33" and "Xinluzao 13" was found to decrease by 18.1% and 13.5%, respectively. The stand establishment rates decreased by 8.4% and 16.5%, respectively, and the degrees of precocity increased by 17.0% and 26.7%, respectively. The density of plastic film residue was found to reach 2000 kg/hm2 after 141 years of continuous film mulching, and the yields of the two varieties decreased by 38.3% and 45.2%. Stand establishment decreased by 13.0% and 21.1%, and degrees of precocity increased by 32.2% and 27.7%. The yield of "Xinluzao 33" decreased significantly when film density was 500 kg/hm2. The yield of "Xinluzao 13" decreased significantly when film density reached 1000 kg/hm2 and decreased again at 2000 kg/hm2. Biomass, root/shoot ratio, and root surface area were significantly different from the control group. High concentrations of plastic film residue caused soil quality to deteriorate and caused uneven distribution of soil moisture. When the density of soil plastic film residue exceeded 1000 kg/hm2, the infiltration of soil moisture was hindered. Soil moisture levels decreased significantly at depths of 30-40 cm. Plastic film residue was found to cause depletion of soil nutrients. When the density of soil plastic film residue reached 2000 kg/hm2, pH increased by 10.1%, and organic matter, alkaline hydrolysis of N, available P, and available K decreased by 16.7%, 55.0%, 60.3%, and 17.9%, respectively. Significance: It is the first time that we studied the effects of plastic film residue accumulation on soil quality and cotton yield by setting density plastic film residue gradients, and made clear the damage degree of film residue. Without timely measures, it will seriously endanger the sustainable development of cotton and the sustainable use of land. We found applying and cultivating deep root system cotton could mitigate the hazards of residual film. This study provided theoretical support for the reasonable preventive measures of government and cotton growers.