Study On The Remediation Of Calcareous Soil Microenvironment By Biochar Under Continuous Cropping Of Flue-cured Tobacco

At present,the researches on biochar remediation of continuous cropping obstacles of flue-cured tobacco are mostly focused on acidic soil,and little attention is paid to calcareous soil.Moreover,the understanding of the effects of biochar on soil nutrient cycling system,microbial community structure evolution and diversity is still very limited,and the mechanism of action on soil microenvironment is far from clear.In this study,the continuous cropping tobacco soil was used as the research object,and the changes of nutrients and enzyme activities in calcareous purple soil under long-term continuous cropping of flue-cured tobacco were analyzed.Then,based on this,corn straw,rice husk and peanut shell biochar were added to continuous cropping tobacco soil at different concentrations as soil amendments to determine soil nutrients,enzyme activities and microbial diversity at different growth stages of flue-cured tobacco.Combined with the agronomic traits of flue-cured tobacco,the experimental data were analyzed by multidisciplinary theories and methods,and the effects of different types and concentrations of biochar on soil microenvironment and the optimal application amount of different biochar were determined.The main conclusions are as follows :(1)Changes of nutrients and enzyme activities in calcareous soil under long-term continuous cropping of flue-cured tobacco.Flue-cured tobacco significantly reduced the surface soil p H,organic matter and alkali-hydrolyzable nitrogen content by 17.43%,18.34% and 23.15%,respectively.The contents of available phosphorus and available potassium increased significantly by 124%and 54.55% respectively.And long-term continuous cropping also reduced urease activity by58.51% ～ 91.28% and sucrase activity by 29.14% ～ 48.66%.Soil nutrients are closely related to soil enzyme activities.Therefore,long-term continuous cropping of flue-cured tobacco resulted in decreased p H,nutrient imbalance and decreased enzyme activity in calcareous soil.(2)Effects of biochar on nutrients and enzyme activities in continuous cropping calcareous soil of flue-cured tobaccoBiochar increased soil p H,organic matter,available phosphorus and available potassium contents to varying degrees.Biochar increased soil invertase,alkaline phosphatase and urease activities as a whole,but the effects of different biochar treatment on soil enzyme activity in each growth period of flue-cured tobacco were different.The details are as follows : At the rosette stage,medium and low concentration biochar treatment(≤0.6%)enhanced soil invertase activity,while high concentration biochar treatment(>0.6%)limited or even reduced invertase activity.For soil urease,biochar treatment reduced soil urease activity at the vigorous growth stage,while increased soil urease activity at the rosette stage and mature stage.Therefore,appropriate biochar concentration is beneficial to improve soil nutrients and enzyme activity.(3)Effects of biochar on microbial community structure in continuous cropping calcareous soil of flue-cured tobaccoBiochar overall improves the abundance and diversity of soil bacteria and microorganisms.It also reduces the abundance and diversity of fungal microorganisms.Biochar treatment also increased the relative abundance of beneficial bacteria in soil.Most biochar treatments increased the relative abundance of beneficial bacteria in soil such as Actinobacteria,Chloroflexi and Mucor.Among them,the best effect is achieved when the concentration of corn corn straw biochar is 0.2%,rice husk biochar is 0.4%,and peanut husk biochar is0.42%.The results of redundancy analysis showed that soil organic matter,sucrase and p H had great influence on bacterial community structure,while soil available potassium,alkaline phosphatase,available phosphorus and organic matter had great influence on fungal community distribution.It indicated that biochar regulates soil microbial community structure by regulating soil nutrients and enzyme activity(especially p H).Therefore,biochar is beneficial to improve the abundance and diversity of soil bacterial microorganisms,increase the abundance of beneficial bacteria,and regulate the soil microbial community structure by affecting soil nutrients and enzyme activities.(4)Effects of biochar on growth of continuous cropping flue-cured tobacco in calcareous soilBiochar can promote the growth of flue-cured tobacco.Different biochar treatments have different effects on the growth of flue-cured tobacco.On the one hand,the optimum concentration of different kinds of biochar is different.For corn straw biochar,the promotion effect is best at a concentration of 0.2%;For rice husk biochar,the best promotion effect is at a concentration of 0.4%;For peanut shell biochar,the promotion effect is better at a concentration of 0.6%.On the other hand,low concentration biochar(≤0.6%)promoted the growth of flue-cured tobacco,while high concentration biochar(>0.6%)inhibited the growth of flue-cured tobacco.Therefore,when we choose biochar as a soil amendment,we should choose the appropriate amount according to the local soil type and biochar type.In summary,long-term continuous cropping of flue-cured tobacco led to a decrease in p H,nutrient imbalance and enzyme activity in calcareous purple soil.Appropriate biochar(≤0.6%)could increase soil p H,balance soil nutrient content.It can also improve enzyme activity and the abundance and diversity of soil bacterial microorganisms,increase the proportion of beneficial bacteria,and promote the growth of flue-cured tobacco.Therefore,the application of biochar to continuous cropping tobacco fields helps to improve the soil microenvironment and eliminate soil fertility barriers.For the problem of soil fertility disorder in calcareous purple soil,biochar can be applied to solve it.However,it is important to select the appropriate and optimal application amount for different types of biochar.Excessive application amount will inhibit soil enzyme activity and affect the growth and development of flue-cured tobacco.However,if the application amount is too low,the improvement effect is small.