Effects Of Excessive Fertilization On Soil Microbial Community Structure

Excessive fertilization can lead to soil acidification and salinization.Especially in the production facilities,a large number of long-term application of chemical fertilizer to soil can lead to NPK nutrient accumulation,serious soil acidification and secondary salinization;with the increase of planting years,soil borne diseases are more and more common,which seriously restrict the yield and quality of vegetable production.These have been widely concerned,However,the effects of soil nutrient imbalance,acidification and secondary salinization on soil microbial community structure and soil borne diseases are not very clear.This test adopt he indoor simulation experiment,which can removal of the effects of crop,to study the soil N、P、K accumulation,acidification and secondary salinization of soil how to directly affect the quantity,community structure and balance,soil borne pathogens to microbial growth and reproduction.The results can provide theoretical basis for rational fertilization and prevention of soil borne diseases.The results are as follows:(1)Compared with the control soil,nitrogen fertilizer increased the soil microbial quantity,the soil culturable bacteria in the increase in the number of the largest proportion,followed by actinomycetes and fungi increased the number ratio of the minimum.When the nitrate nitrogen content was 134.89 mg/kg,ammonium nitrogen content was 45.51 mg/kg,the number of culturable bacteria in soil decreased;When the nitrate nitrogen content was 127.75 mg/kg,ammonium nitrogen content was 38.79 mg/kg,the growth of actinomycetes in soil was inhibited;The culturable fungi,especially the pathogenic fungi,the most resistant to nitrogen in the soil,could be increased by increasing the amount of nitrogen in the soil.(2)After applying nitrogen fertilizer,there was a significant negative correlation between the number of culturable microorganisms and soil pH.Path analysis showed that soil EC and NH4+-N content had a direct impact on the number of culturable bacteria in the soil,and the effect of NO3--N content on the number of culturable bacteria was indirectly affected by the electrical conductivity.The content of NO3--N had a direct effect on the quantity of soil actinomycetes.EC and NH4+-N content had a direct impact on the number of culturable fungi in soil,the size of which was EC>NH4+-N.Water soluble salt content had a direct effect on the number of culturable bacteria in soil;NO3--N had an indirect effect on the number of culturable bacteria in soil.(3)Compared with the control soil,P fertilizer increased the soil microbial quantity,the soil culturable bacteria in the increase in the number of the largest proportion,followed by actinomycetes and fungi increased the number ratio of the minimum.The amount of bacteria,fungi and actinomycetes in soil was inhibited when the P application rate was greater than the content of available P was 104.81 mg/kg,but the number of Fusarium oxysporum was still increasing.With increased from P3 to P4 treatment,soil culturable actinomycetes and the number of bacteria decreased rapidly,while the number of soil fungi was decreased,but the difference was not significant(P<0.05),the number of pathogenic fungi of Fusarium oxysporum is still a rapid increase.(4)Compared with the control soil,the application of potassium fertilizer increased the number of culturable microorganisms in the soil,in which the proportion of culturable bacteria was the largest,followed by fungi,actinomyces was least.When the amount of potassium was greater than the content of available K was more than 313.15 mg/kg,the number of culturable Actinomyces in soil decreased,the growth was inhibited,and the number of fungi increased,especially the number of pathogenic fungi Fusarium wilt will increase rapidly.The ratio of Fusarium oxysporum and fungi began to increase.(5)After the application of potassium fertilizer,soil culturable microorganisms were significantly negatively correlated with soil pH and negatively correlated with water soluble salt content.Path analysis showed that the number of culturable bacteria was more than pH.Soil EC and pH had a direct effect on the number of culturable fungi in soil,and the content of soluble salt in soil had an indirect effect on the quantity of soil.The conductivity had a direct effect on the number of culturable actinomycetes in soil,and the content of soluble salt in soil had an indirect effect on the quantity of soil.Electrical conductivity and pH had a direct effect on soil culturable Fusarium wilt.(6)Compared with the control soil,N1P1K1 and N2P2K2 were increased in soil culturable actinomycetes;N1P1K1,N2P2K2 and N3P3K3 treatment increased the amount of bacteria in the soil;and soil fungi,especially pathogenic fungi,Fusarium oxysporum increased with the increase of fertilizer,especially the rapid increase in N3P3K3 and N4P4K4.The application of N,P and K had the greatest effect on the number of soil culturable fungi,especially the pathogenic fungi,Fusarium oxysporum.Path analysis showed that the content of available phosphorus and NH4+-N content of soil has good direct effect on cultured bacteria number;the content of available P and pH have better effect on soil culturable fungi,NH4+-N and NO3--N content through the influence on pH has indirect influence on the number of soil culturable fungi;the content of NH4+-N on soil culturable directly affects on the number of actinomycetes;EC had a direct effect on the number of culturable bacteria in soil.,the NO3--N content has a good indirect effect on the number of culturable bacteria in soil.