Remediation Effect Of Reductive Soil Disinfestation And Biochar On Soil Continuous Cropping Obstacles

Reductive soil disinfestation（RSD）,is a pre-planting soil management practice to restore degraded facility vegetable soil,which incorporates easily decomposable organic materials into soils,followed by irrigating and covering the soils with plastic films to create highly reduced soil conditions,but it will also lead to a large amount of N₂O emissions in the process of restoration.Studies have shown that biochar application can reduce N₂O emission and also be used for prevent continuous cropping obstacle.Although studies on the effects of RSD and biochar combined remediation on soil greenhouse gas emissions have been reported,the conclusions are not consistent.Meanwhile,the effects of RSD and biochar restoration on dissolved organic mater（DOM）and continuous cropping obstacle restoration effects are still unclear.In this study,performed four treatments,i.e.,soil without any amendment as control（CK）,soil amended with 2%（w/w）rice straw（RSD）,soil amended with 2%（w/w）biochar（BC）,and soil amended with 2%（w/w）rice straw and 2%（w/w）biochar（RSD+BC）.（1）Compare their influences on soil enzyme activities and greenhouse gas emissions and analysis of environmental factors,enzyme activities and greenhouse gas emissions inherent correlation.（2）Used spectral techniques to study the effects of different restoration treatments on soil DOM content and spectral characteristics.（3）A field experiment was conducted to study the effects of different remediation methods on soil microbial diversity and community composition.The results of the culture experiment were as follows:the activities ofβ-glucosidase（βG）,cellobiohydrolase（CBH）,peroxidase（PEO）,β-1,4-N-acetylglucosaminidase（NAG）,acid phosphatase（AP）,and the values of enzyme C/P and N/P were significantly increased in RSD and RSD+BC treatments compared with CK（P<0.05）,but there was no significant difference on enzyme activities in BC treatment.Soil CO₂ emissions in RSD,BC,and RSD+BC treatments were increased by 10.6,1.1,and 12.2 times,respectively.Soil N₂O emission in RSD treatment was also significantly increased,but significantly decreased in BC and RSD+BC treatments（P<0.05）.Compared with RSD treatment,RSD+BC treatment notably decreased N₂O emission and global warm potential（GWP）by 86.9%and 37.8%.Structural equation model analysis also indicated thatβG and dissolved organic carbon（DOC）had a direct positive effect on soil CO₂ emission,andβG and CBH indirectly influenced CO₂ emission by affecting the DOC content.Moreover,soil NO₃^--N and NH₄⁺-N had a direct negative effect on N₂O emission.The contents of DOC in RSD,BC and RSD+BC treatments were increased by 142.9%,24.6%and 127.0%in relation to CK.Compare with the RSD treatment,the RSD+BC treatment significantly reduced the DOC content（P<0.05）.Soil DOM was mainly composed of fulvic acid-like and humic acid-like material,and RSD treatment improved the humic acid-like component,whereas RSD+BC treatment was more conductive to the increase of fulvic acid-like substances.RSD,BC and RSD+BC treatments significantly enhanced the degree of aromatization and humification of soil DOM.Structural equation model analysis also showed that soil p H had a direct positive effect on DOC content and humification index（HIXem）and Eh had a direct negative effect on DOC content.Meanwhile,soil p H also indirectly affects microbial biomass carbon（MBC）and fluorescence index（FI）due to DOC change.In the present field study,which were treated with different management practices,i.e.,1)soils incorporated with 1%（w/w）alfalfa residues,flooded and covered with plastic film（RSD）,2)soils incorporated with 1%（w/w）biochar（BC）,3)soils incorporated with 1%（w/w）alfalfa residues and 1%（w/w）biochar,flooded and covered with plastic film（RSD+BC）,4)soils untreated（CK）,5)soils flooded（SF）,and 6)soils flooded and covered with plastic film（SFF）.The RSD and RSD+BC treatments decreased nitrate（NO₃^--N）concentrations while increasing soil p H,ammonium（NH₄⁺-N）,dissolved organic carbon（DOC）,and reduced ions(Fe²⁺,Mn²⁺)concentrations.Compared to the CK,SF,and SFF,the RSD and RSD+BC treatments decreased the bacterial and fungal abundance and diversity,which however was not observed in the BC treatment.The RSD treatment significantly inhibited the relative abundance of genus Fusarium while increasing the relative abundance of genus Bacillus and Clostridium（P<0.01）,which was more evident in the RSD+BC treatment,suggesting that integrations of biochar with RSD inhibited pathogenic fungi while increasing beneficial bacteria abundance.In addition,compared with CK treatment,BC,RSD and RSD+BC increased pepper yield by 27.4%,55.3%and44.4%,respectively.Pepper yield was significantly positively correlated with soil DOC,NH₄⁺-N concentration,relative abundance of Bacillus and Clostricium（P<0.01）,and negatively correlated with relative abundance of NO₃^--N and Fusarium（P<0.05）.Therefore,considering the basic properties of soil,greenhouse gas emission reduction,DOM characteristics,microbial population change and field yield,the combination of RSD and biochar has better effect on the remediation of continuous cropping obstacles.