Abstract: An experiment was carried out based on long-term fertilizer experiments in fluvo-aquic soil in Changping County, Beijing, China, to study effects of long-term different fertilization systems on soil microbe and its relation to soil fertility. The main results are as follows: (1) The amount of soil bacteria and fungi of the treatments of applying chemical fertilizers only were less than that of long-term fallow soil, but actinomycetes were by contrary. (2) Combined applying chemical fertilizers only had higher amount of actinomycetes and similar amount of bacteria and fungi compared with the soil without fertilizer-applied. (3) Soil of balanced fertilization of N, P, K (NPK treatment), as a whole, had similar amount of bacteria, fungi and actinomycetes with N, NP, NK, PK treatments (unbalanced fertilization). (4) Combined application N, P, K chemical fertilizers with manure or crop straw had a significant effect of increasing amount of soil microbe. Treatments of NPK+M, NPK+1.5M and NPK+S not only had more amount of soil bacteria, fungi and actinomycetes than those of in CK, N, NP, NK, PK, NPK treatments, but also had more amount of bacteria and actinomycetes than and similar amount of fungi with that of in fallow soil. (5) Treatments of long-term applying chemical fertilizers only had less amount of nitrogen-fixing bacteria, ammonifers, cellulose-decomposing and denitrifying bacteria, but higher amount of nitrifying bacteria than that of fallow treatment. Soils of applied with chemical fertilizers only had more numerous amount of nitrogen-fixing, nitrifying and cellulose-decomposing bacteria but less numerous amount of ammonifers and denitrifying bacteria compared with that of in no fertilizer-applied soil. Soil of balanced fertilization of N, P, K (NPK treatment) had more amount of ammonifers, nitrifying and cellulose-decomposing bacteria, similar amount of nitrogen-fixing bacteria and less amount of denitrifying bacteria than that of in soils of unbalanced fertilization treatments (N, NP, NK, PK). Combined use of N, P, K chemical fertilizer with manure or crop straw promoted the increase of the amount of nitrogen-fixing bacteria, ammonifers, denitrifying, nitrifying and cellulose-decomposing bacteria. The amount of these physiological functional microbe in NPK+M, NPK+1.5M and NPK+S treatments were higher than that of in those treatments of only applied with chemical fertilizers. NPK+M, NPK+1.5M and NPK+S even had more amount of nitrogen-fixing bacteria, ammonifers, denitrifying and nitrifying bacteria than that of in fallow soil. (6) There was a positive correlation between the contents of soil nutrient and amount of soil microbe.

Key words: Fertilization systems, Long-term fertilizer experiment, Soil microbe, Soil fertility