| Soil microbe is the major part of the decomposers in the continent ecosystem. As well it takes part in several physiologic activities including the decomposition of organic matter, the conversion of nutrition, the stimulation or depression of plant growing, and also all kinds of physical processes in soil. Microorganisms are really important bioindicators of soil quality, and thus they can be used to monitor the changes of soil quality. Microcalorimetry is a new technique to determine microbial activity rapidly, and so it is extensively applied in the measurement of the thermal effect produced by soil microbial metabolism. There were many researches using microcalorimetry in our domestic country, including the influence of drugs, pollutants, heavy metals and rare earth elements on the bacterial growth and cell metabolism, the function of macromolecules, or the interaction between cells etc., but rarely in the field of soil microorganisms. In this experiment, we collected five fertilizer samples in the surface of soil (5-15cm), including N (nitrogen), NP (application of nitrogen and phosphorus), SNP (application of straw, nitrogen and phosphorus), M (manure) and MNP (application of manure, nitrogen and phosphorus), and also a sample without fertilizer CK (the control). We took MNP and CK as the representative, collecting five soil samples respectively at different depths (5-15cm ,15-20cm ,25-30cm ,35-40cm ,45-50cm). In this paper, we studied the changes of soil microbial activity in level of horizontal and vertical space under the long-term fertilization and crop rotation in wheat fields. The main experiments results were summarized as follows:1. Different fertility treatments had different soil microbial activity. Shapes of thermal power-time curves of different fertility treatments are different. Curves of MNP, NP and SNP were steep, and curves of M, N and CK were flattening. Values of parameters of microcalorimetryμ(microbial growth rate constant), Q_t (the total heat of microbial metabolism), P_h (peak height of power-time curves) of MNP, NP and SNP were high, and value of P_t (time reaching the peak of power-time curves) was low. So fertility application treatments of manure plus nitrogen and phosphorus (MNP), straw plus nitrogen and phosphorus (SNP) and nitrogen plus phosphorus (NP) significantly increased microbial activity in wheat soil; application of single nitrogen fertilizer or single kind of organic fertilizer had no significant difference with the control (CK). 2. Microbial activity had the basic trend that decreased with the depth in soil. Fertilization increased microbial activity in almost all soil layers measured. There were different shapes of thermal power-time curves in no fertilizer application treatment(CK) and mineral fertilizer plus manure application treatment(MNP), particularly in the former two layers of soil samples. Curves of MNP are obviously steeper than the CK, and their shouders before the peak were significantly much shorter; the P_h andμvalues of MNP are greater than CK, and the P_t values of MNP were less than the CK.3. In different fertilization treatments, number of soil bacteria and fungi in sample M was the highest, then following with MNP, NP and SNP. Only the number of bacteria in sample N increased. The relationship between bacteria and different nutrients was inconsistent. And the relationship between the number of bacteria and total phosphorus achieved significant correlation level. When compared with the parameters of microcalorimetry, the relationship was not so good. However, the number of bacteria in different depths of soil has good correlation with microbial activity (value of P_t). Such a difference occurred may be mainly because there was small disturbance in the deep soil. So soil microbial community structure was relatively stable. In addition, fertilization treatments had increased the number of bacteria in the deep layers of soil.4. Soil microbial activity and the number of microorganisms were significantly affected by soil available phosphorus. The relationship between the parameters of microcalorimetry was good. The relevance of microbial activity and other soil nutrients was complex.5. Compared with the control, long-term application of manure and manure plus inorganic fertilizer remarkably increased the nutrient content in soil; straw plus phosphate and nitrogen increased most of the nutrient content in soil; application of nitrogen plus phosphate fertilizer increased soil organic carbon, total phosphorus and available phosphorus content; the single application of nitrogen fertilizer slightly increased soil organic carbon content; other soil nutrient content of was similar or much lower.In this study, long-term fertilization of soil conditions changed the number of microbes and microbial activity, and also changed the conditions of soil nutrients. This showed, in the long-term fertilization conditions, the soil microbial community structure or function were changed, and this change was closely related to changes in the environment in soil, that was the change of soil quality or soil fertility, which might be further affect crop yields.
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