Effect Of Organic Substitution Of Chemical Fertilizer On Soil Carbon Pool And Micro-ecological Environment In Continuous Peanut Cropping Field

Continuous cropping of peanuts and continuous application of chemical fertilizers may lead to the imbalance of soil carbon pool and the decline of soil quality.In order to reveal the effect of organic substitution of chemical fertilizer on soil carbon pool and micro-ecological environment in continuous peanut cropping fieldas well as the effective mechanism,four complete random block groups were set up and the treatments of vermicompost combined with chemical fertilizer（VM）,bio-Organic substitution of chemical fertilizer combined with chemical fertilizer（BF）,total-chemical fertilizer（CF）and no-fertilizer control（CK）were carried out in the continuous peanut cropping fields for 5 years.Soil carbon pool and microbial indicators were determined in peanut podding and harvesting periods.The microbial mechanism of soil organic carbon accumulation in continuous peanut cropping fields under organic substitution of chemical fertilizers was analyzed.The research results provided a scientific basis for better allocation of farmland management measures and promotion of soil ecological restoration as well as alleviate the obstacles to continuous peanut cropping.The main findings obtained were as follows:1.Under the condition of organic substitution of chemical fertilizers in the continuous cropping peanut field,the soil organic carbon content showed the change rule of VM>BF>CF>CK.The contents of soil organic carbon（TOC）,easily oxidizable organic carbon（ROC）,microbial biomass carbon（MBC）,mineralizable organic carbon（PCM）and soil carbon pool management index（CPMI）in the VM and BF treatments were significantly higher than CF,CK treatment,and the pod setting period was higher than the harvest period,the VM effect was the most significant（P<0.05）.The effective rates of MBC,PCM and soluble organic carbon（DOC）in organic fertilizer replacement soil were significantly lower than those of CK and CF.Principal component analysis and correlation analysis showed that organic substitution of chemical fertilizers was significantly positively correlated with TOC and active organic carbon content,and negatively correlated with soil active organic carbon except ROC;CPMI was positivelycorrelated with ROC,MBC,DOC,and PCMsignificantly or extremely（P<0.05,P<0.01）.2.The analysis of the PLFA content of soil samples showed that the total PLFA content was the highest in VM and the lowest in CK.Compared with CK and CF,the bacteria PLFA contents,actinomycetes PLFA contentsandfungi PLFA contents in VMand BF allincreasedsignificantly.The composition and diversity of soil microbial community changed significantly compared with CK and CF.Redundancy analysis and stepwise regression analysis showed that VM and BF treatments were positively correlated with PLFA contents of various groups of soil microorganisms,especially VM treatment had the strongest correlation.CK and CF treatments were negatively correlated with all other variables except G⁺/G^-ratio.The contents of TOC and its components were significantly or extremely significantly correlated with the PLFA contents of various soil microorganismgroups.3.Compared with CK and CF,the contents of soil microbial biomass nitrogen and phosphorus in VM and BF treatments were significantly increased（P<0.05）,and VM treatment had the best effect,and the pod setting period was higher than that in harvest period.Soil microbial biomass nitrogen and phosphorus contents under different treatments varied in the range of 18.50mg·kg^-1～37.98mg·kg^-1,2.56mg·kg^-1～5.14mg·kg^-1.MBC/MBN varied in the range of 7.71～9.15 under different treatments.4.The number of culturable microorganisms in different treatments showed the distribution law of bacteria>actinomycetes>fungi.The number of culturable bacteria in the soils of VM and BF was significantly increased compared with those of CK and CF treatments,and the pod setting stage was higher than that in the harvest stage.The number of soil fungi and actinomycetes showed different changes in different treatments and sampling stages.5.The comprehensive fertility index（IFI）ranged from 0.88 to 0.99 at the podding stage.The harvest period was between 0.87 and 0.93,Among them,the IFI value of VM treatment was the largest,and the IFI value of CK was the smallest.The peanut yield of VM and BF treatment was significantly higher than that of CK and CF（P<0.05）.In conclusion,the continuous cropping of peanuts seriously deteriorated the soil environment and significantly affects the yield of peanuts.Organic substitution of chemical fertilizers significantly increased the content of soil active organic carbon,and at the same time contributed to the accumulation of soil inactive organic carbon.The composition and structure of soil microbial community were significantly changed by organic substitution of chemical fertilizers and its diversity increased.The increase of exogenous organic carbon caused by organic fertilization and the subsequent changes of soil microbial community are the driving factors of TOC accumulation in continuous cropping peanut fields,and soil microbial activity is the key factor affecting TOC accumulation.Organic fertilizer,especially vermicompost,has a significant effect on improving the soil quality of continuous peanut cropping fields and alleviating the continuous croppingobstacles.This paper has 27 pictures,17 tables and 147 references.