Effects Of Changes In Physicochemical Properties Of Acid Modified Biochar On Soil Properties And Cucumber Wilt Disease

Biochar can improve the soil environment,affect soil microorganisms,induce plants to produce systemic resistance,and then affect plant disease.Cucumber wilt,as a soil borne disease caused by Fusarium oxysporum,has the characteristics of strong explosiveness,large damage area,and difficult control.Acid-base modified biochar may have a stronger effect on soil improvement by changing the functional group composition of biochar.Does modified biochar have a certain regulatory effect on cucumber wilt disease,and what is its mechanism of action?At present,it is not very clear.Answering these questions is helpful for using biochar for cucumber wilt control practices.Based on this,this study screened acid-base modified biochar materials and set up experiments to control the impact of biochar on cucumber wilt disease.The changes after modification of biochar are mainly analyzed through indicators such as elemental composition,surface functional groups,crystal structure,p H and conductivity,and soluble carbon and nitrogen.Acid modified biochar and unmodified biochar were applied to soil inoculated with cucumber wilt disease.The cucumber disease index,soil physical and chemical properties,soil microbial community,biochar physical and chemical properties,as well as the relationship between soil physical and chemical properties and soil microbial community were analyzed.The effects of biochar physical and chemical properties on soil properties and cucumber wilt disease were further studied.The main research findings are as follows:（1）The carbon ratio of acid modified biochar and alkali modified biochar decreased by 6.98%and 5.76%,respectively（p<0.05）,and the nitrogen ratio also decreased by 0.11%and 0.16%,respectively（p<0.05）.Alkali modified biochar can increase the number of functional groups in biochar,while acid modified biochar can increase the variety and quantity of functional groups in biochar.After acid modified biochar,the total soluble carbon content of biochar significantly decreased by 7.922mg·L^-1.The total soluble carbon content of alkali modified biochar increased by 4.821mg·L^-1.After acid modification,the soluble total nitrogen content of biochar decreased by 13.868 mg·L^-1,while the soluble total nitrogen content of alkali modified biochar decreased by 11.957 mg·L^-1（p<0.01）.After acid modified biochar,the diameter of the pathogen hyphae increases with the increase of the proportion of biochar added.The diameter of the pathogen hyphae of alkali modified biochar did not change significantly with the increase of the proportion of biochar added.（2）The disease index of cucumber without adding biochar was 33.17.The addition ratio of biochar and biochar has an interactive effect（p<0.05）.Under the condition of 1%biochar application,the initial biochar（O-BC）had the highest cucumber disease index（34.77）,while under the condition of 3%biochar application,the cucumber disease index was the lowest（27.62）.Acid modified biochar（AC-BC）showed the highest cucumber disease index（38.40）under 5%biochar application conditions,and the lowest cucumber disease index（28.92）under 3%biochar application conditions（p<0.05）.（3）Adding biochar to soil can alter the carbon and nitrogen components of the soil.Initial biochar can increase soil total carbon(1.677 g·kg^-1),nitrate nitrogen content(9.569 mg·kg^-1),reduce soil ammonium nitrogen(0.823 mg·kg^-1),and soluble inorganic carbon content(8.481 mg·kg^-1).Acid modified biochar can increase soil total carbon(1.149 g·kg^-1),nitrate nitrogen content(7.460 mg·kg^-1),reduce soil ammonium nitrogen(0.771 mg·kg^-1),and soluble inorganic carbon content(7.616mg·kg^-1).（4）The number of OTUs for all tested soil microorganisms is 5507,with the highest OTUs specific to O-BC soil being 287,the lowest OTUs specific to AC-BC being 278,and CK being 62.The ace index of the bacterial community in O-BC significantly increased by 115.02（p<0.05）,while AC-BC did not significantly increase the ace index of the bacterial community.The total number of OTUs shared by the three is 997,with the highest number of AC-BC specific OTUs being 260,the lowest number of O-BC specific OTUs being 238,and the lowest number of CK being 90.Compared with CK,the fungal community ace index of O-BC and AC-BC significantly increased by 21.40 and 31.32,respectively（p<0.05）.（5）The correlation heat map and structural equation model indicate that changes in soluble carbon and nitrogen,p H,and EC values in biochar can have an impact on the carbon and nitrogen components in the soil,especially on the total carbon,organic carbon,and inorganic nitrogen in the soil.Changes in soil physicochemical properties can also affect changes in microbial communities.The changes in soil physicochemical properties and microbial communities can directly affect the disease index of cucumber wilt disease.In summary,acid modified biochar can significantly alter the physicochemical properties of biochar compared to alkali modified biochar.The addition of biochar can promote cucumber growth and inhibit the occurrence of cucumber wilt disease.The initial biochar and acid modified biochar have the best control effect on cucumber wilt disease at a 3%addition ratio,and the initial biochar has a stronger control effect.The changes in the physicochemical properties of biochar have a significant impact on soil physicochemical and microbial communities,thereby affecting cucumber wilt disease.Therefore,this study can provide theoretical basis for the early control of agricultural diseases and the application of biochar in soil.