Response Evaluation Of Available Phosphorus To Farmland Soil Microplastics In Loess Area

The excessive use of chemical products affect soil nutrient supply and pose a potential threat to the environment.Phosphorus is an essential element for the agricultural crops growth.Due to the excessive input of phosphorus-containing fertilizers and the phosphorus adsorption by soil,legacy phosphorus remains in soil and its availability decrease.Plastic film mulching is a necessary measure to increase grain production.Inappropriate film recycling results in numerous residual microplastic particles,which are decomposed from plastic debris,remaining in the soil.Microplastic particles have the property of adsorbing hazardous elements owing to its big specific surface area.Therefore,microplastic particles can affect the fate of hazardous elements.However,how residual microplastic particles and legacy phosphorus affect the functions of agricultural ecosystem,especially how residual microplastic particles affect the supply of phosphorus,remains unclear.Mollisols,entisols,anthrosols and aeolian sandy soil,which are typical agricultural soils in the Loess Plateau are fertilized perennially.It has been found that there was microplastic pollution in agricultural soil in Shaanxi area of the Loess Plateau.In this study,batch incubation experiments were conducted to explore the effects of conventional microplastics(PE,PS,PVC)and biodegradable microplastics(PBS,PLA)on soil phosphorus availability.In addition,microplastic concentrations(0 %,0.5 %,1 %,2 %,5 %,7 %,10 %)and microplastic sizes(25 ± 10 μm,150 ± 10μm,270 ± 10 μm,550 ± 10 μm)were set to explore the effects of microplastics properties on soil available phosphorus content.Moreover,soil clay content determination and soil aggregates fractionation(0～0.5 mm,0.5～2 mm)was conducted to explore the effects of the two soil factors on phosphorus availability in microplastics-polluted soil.Finally,different concentrations of fulvic acid were added to explore the effect of organic matter on the adsorption of phosphorus by microplastics.The results were as follows:(1)Olsen-P content was 50% higher in biodegradable microplastics treatment than in conventional microplastics treatment.With the increase of microplastics concentration,phosphorus variation tendency differed in different microplastics types addition treatments.When the PE and PLA concentration are 5 %,the soil Olsen-P content was the lowest.PVC treatments showed a decreasing tendency with the increase of microplastics concentration,and the soil Olsen-P content was the lowest in the concentration of 10 %.With the increase of microplastics size in PE and PLA treatments,the soil Olsen-P content increased in the order of 25 ± 10 μm < 150 ± 10μm < 270 ± 10 μm < 550 ± 10 μm.There was no significant difference in soil Olsen-P content among the PVC sizes.(2)Microplastics could reduce the soil Olsen-P content,but Olsen-P variation range differed in different microplastics types and soil types.The lowest reduction range of Olsen-P was 0,and the highest was 48.7%.Soil clay content may be an important factor affecting Olsen-P content in microplastics-polluted soil.Olsen-P content decreased by 17.9%-48.7% in high-clay and microplastic-polluted soil(anthrosols),whereas it exhibited similar values in high-sand and microplastic-polluted soil(aeolian sandy soil).In the same soil type,the effect of microplastics on Olsen-P content in 0～0.5 mm-size soil aggregates was more pronounced than that in 0.5～2 mm-size soil aggregates.(3)Organic matter(fulvic acid)could reduce the adsorption of phosphorus on microplastics.In microplastic-polluted mollisols,the Olsen-P increase extent induced by the same organic matter was in the order of PLA > PE > PVC.In microplastic-polluted aeolian sandy soil,the Olsen-P increase extent induced by the same organic matter was in the order of PVC > PE > PLA.Microplastics can adsorb phosphorus.The adsorption capacity of phosphorus on conventional microplastics(PE,PVC)to was higher than that on biodegradable microplastics(PLA).Residual microplastics can result in soil Olsen-P reduction in agricultural soil.Moreover,the effects of microplastics properties(types,concentrations,sizes)and soil properties(soil clay content,soil aggregates fractionation,and organic matter content)on phosphorus availability were emphasized in this study.Based on these results,the negative impact of the chemical products input,such as chemical fertilizers and plastic films,should receive widespread concern in future agricultural production.Source control,innovative management and reasonable use-recovery mode can fundamentally solve the problems brought by chemical products to agricultural ecosystems,so as to maximize agricultural economic and ecological benefits.