Effects Of Long-Term Fertilization On Soil Microbial Commutity Structure Of A Loessial Soil

Human activities especially fertilization or manuring impose strong impact on soil physical and chemical properties, thus inevitably has a significant effect on both bialmass and community structure of soil microbial organism, which is the most important component of soil ecosystem. On the basis of two long term experiments conducted in the "National Soil Fertility and Fertilizer Efficiency Monitoring Base on Loess Soil" This paper looked at the effects of different fertilization on microbial biomass and its community structure expressed as phospholipds fatty acids (PLFAs). The results obtained are as follow:1,Under rainfed condition, application of balanced inorganic fertilizers (NPK),absolute fallow (Setaside), especially inorganic fertilizers plus organic manure significantly improved soil chemical properties, promoted the growth of various microbial community, and increased soil microbial biomass content. Application of nitrogen alone (N) or combination of phosphate and potassium fertilizers (PK) showed a less effect on soil microbial biomass C (SMBC) level than NPK treatment did. The PK application showed a slight stress on microbial growth. The fact that the ratio of Fungal PLFAs content to bacterial was the highest on control treatment may implied that the fungi community had a high survival ability in the barren soil than other microbial communities.2,The microbial as well as chemical properties were compared for soils collected from rhizosphere and non rhizosphere at plough layer (20cm) in a irrigated fertilization experiment. The results showed that application of organic materials improved the living environment of soil microbial organisms and thus its growth. As a result, the SMBC was markedly increased on plots receiving stalk plus NPK and organic manure in addition of NPK. The NPK treatment promoted the growth of fungi while the PK application stressed the growth of microbial organisms. The results also indicated that the SMBC were increased in rhizospheric soils compared to non-rhizosphere soils for all theaments, the PLFAs levels showed the same trends as that of SMBC apart from than on SNPK treated soil. the Cy17:0 only existed in the NPK,MNPK and SNPK treatments in the rhizospere and bulk soil.3,The correlation between soil microbial community structure expressed as PLFAs concentration and soil chemical properties were analyzed. The results showed that bacterial PLFAs, actinomycete PLFAs as well as total PLFAs contents had significant positive linear correlationships with soil organic matter, total soil nitrogen, soil Olsen P and soil extractable K, but negatively correlated to soli pH value. Soil fungal PLFAs was found no significant correlation with soil Olsen-P. What's more, The correlation coefficients of bacteria, actinomycetes and total PLFAs with total nitrogen were higher than those with SOM and Olsen-P.