The degradation laws of different types of mulch films and their influence on soil physical and chemical properties
As the largest producer and consumer of plastic films in the world,China is faced with serious soil pollution caused by traditional plastic films.Biodegradable mulch brings new controversy while solving this problem.Film mulching changes the soil hydrothermal cycle and has an impact on soil physical and chemical properties.However,the effects of different types of mulch films on soil physical and chemical properties and the differences in their degradation characteristics need to be further studied.In this study,seven types of plastic films were selected:bio-permeable black film(IB),bio-permeable white film(IW),bio-permeable grey film(IG),biodegradable black film(DB),biodegradable white film(DW),polyethylene black film(AB),and polyethylene white film(AW).Xenon or ultraviolet lamps were used to investigate the influence of different kinds of mulch films on the physical and chemical properties of soil and their degradation characteristics.After 35 days of aging with xenon or ultraviolet lamp,other treatments were compared with CK.Xenon lamp and DW treatments significantly increased soil pH the most,by 0.2,whereas UV lamp and DW treatments significantly increased soil organic matter content the most,by 2.93 g·kg-1.UV lamp and IG treatments increased soil cation exchange the most,by 8.28 cmol·kg-1,but the difference was not significant.The use of mulch films can promote the conversion of nitrate nitrogen to ammonia nitrogen.In terms of mulch film degradation,non-degradable mulch films almost do not degrade in the short term under light.The degradation rates of degradable mulch films was higher under ultraviolet lamps than under xenon lamps.The degradation rate of plastic films under xenon lamps was in the order IG＞IB＞IW＞DW≈DB,while the aging degradation rate of mulch films under UV lamps was in the order DB＞IG≈IB＞DW≈IW.Molecular bond breaking and functional group changes occur during film degradation,mainly changing in the relative content of the functional group,which leads to the cracking of the mulch film and the formation of microplastics,causing harm to the soil environment.Mulch films have positive effects on soil physical and chemical properties in the short term.Bio-permeable films degrade faster than biodegradable films and maintain their integrity in the short term,making them suitable for crops with shorter growth cycles.However,biodegradable membranes produce more microplastics,which harm the soil environment.
non-degradable mulching filmdegradable mulching filmphysicochemical properties of soildegradation rulemicroplastics
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