Effect Of Humic Acid And Its Biodegradable Film On The Apple Replant Soil Environment And The Growth Of Seedlings

Due to limited land resources,continuous crop cultivation is unavoidable and can lead to the continuous crop barrier,resulting in slow growth and development of plants,deterioration in fruit quality,and increased damage from pests and diseases.The most common method to overcome the apple replant disease（ARD）is chemical reagent of soil.Due to its harmful effects on human health and the environment,it is being gradually banned.In preliminary research,1.5 g·kg^-1humic acid was found to significantly promote the growth and development of apple seedlings,while humic acid biodegradable films were found to be effective in storing soil moisture,increasing water and fertilizer yield,promoting nutrient conversion,and mitigating the environmental impacts of common mulch.However,the effects of humic acid and its biodegradable film on ARD,as well as the impact of the fragments of broken humic acid biodegradable film on soil quality,were still unknown.This experiment employed a combination of soil simulation and pot experiments to investigate these effects and simulate biodegradable film degradation conditions,ultimately providing a sustainable solution for preventing and controlling ARD.The following sections present the primary research contents and findings of the experiment:（1）The experiment was conducted from March 2022 to February 2023 in the root cellar of Shandong Agricultural University,under natural conditions using five treatments.These treatments consisted of continuous soil（CK）,continuous soil fumigated with bromomethane（FM）,continuous soil with 1.5 g·kg^-1humic acid（A1）,continuous soil covered with humic acid biodegradable film（A2）,and continuous soil with 1.5 g·kg^-1humic acid followed by film（A3）.Samples were taken during four seasons,May 2022（summer）,August 2022（autumn）,November 2022（winter）,and February 2023（spring）.The results showed that the composite treatment,using humic acid and its biodegradable film,significantly increased the number of beneficial microorganisms,decreased the number of harmful fungi,and increased soil enzyme activity,fungal population,soil nutrient content throughout all four seasons.（2）Pot Experiment:In order to investigate the impact of the degradation of humic acid biodegradable film on the continuous soil environment and the growth of apple seedlings,a simulation experiment was conducted.This experiment aimed to examine the effect of degradation products on the continuous soil environment by cutting the humic acid biodegradable film into 1 mm pieces and mixing it with humic acid and continuous soil thoroughly.Five treatments were established,including continuous soil（CK）,continuous soil fumigated with bromomethane（FM）,continuous soil+1.5 g·kg^-1of humic acid（A1）,continuous soil+humic acid biodegradable film（A2）,and continuous soil+humic acid biodegradable film+1.5 g·kg^-1of humic acid（A3）.The results showed that the addition of 1.5g·kg^-1humic acid and humic acid biodegradable film provided the most significant improvement in the growth and development of Malus hupehensis seedlings and soil environment.The addition of these substances also led to an enhancement in biomass（plant height,ground diameter,dry weight,fresh weight）,root morphology（root length,root surface area,root volume,root tip number）,root and leaf antioxidant enzyme activity of Malus hupehensi seedlings.Moreover,an increase in the number of beneficial bacteria and a decrease in harmful fungi,especially pathogenic fungi such as Fusarium,were observed in the continuous crop soil.Soil enzyme activity and nutrient content were also increased,which improved the soil environment.Further correlation analysis of soil enzyme activity,soil microbial population,and soil nutrients demonstrated that the increase in soil nutrient content promoted an increase in soil enzyme activity and microbial population.