| The soil nitrogen is the most important component of soil fertility and the main source of crop’s nitrogen nutrition. Most soil nitrogen cannot meet the crop growth needs, it depends on fertilization to complement and adjust. A large number of organic nitrogen is convernted into inorganic nitrogen through mineralization which satisfy the crops demands, ammonium nitrogen which has comed from soil nutrient mineralization and fertilizer is convernted into nitrate nitrogen by nitrification. Mineralization of nitrogen from various sources can contribution significantly to soil nitrogen budget to total plant nitrogen availability, and to environmental quality and global change. And ammonia oxidation is the first and rate-limiting step in nitrification, which plays a central role in the global nitrogen cycle. The study in this thesis is based on a long-term fertilization experiment located at Beibei District, Chongqing City, and it has lasted for22years. We analyzed the soil nutrients firstly. Then waterlogging incubation method proposed by Warning was used to investigate N mineralization characteristic. The total number of soil nitrobacteria, the potential nitrification rate and the intensity of soil nitrification were studied. And also the aboundance and community structure were compared under different fertilization treatments in order to improve the efficiency of nitrogen utilization and explicate the important role of different fertilizer systems on neutral purple soil fertility buildup and evolution. The main results of the thesis are listed below:(1) Long-term fertilization changed the soil nutrient content. Non-fertilization (CK) and manure (M) decreased the content of soil total nitrogen significantly, Organic C/Total N was increased significantly in treatment M, while fertilization with N and NPK induced the deficit of soil K. Yield-increase rate was increased significantly in treatment NPK+M. Higher values of available P and available K were found in treatment NPK+M. Long-term fertilization with chemical N increased soil NH4+-N and NO3-N significantly. Results showed all fertilization treatments decreased soil pH significantly and the lowest pH as5.57in chloride-containing fertilizer and organic fertilizer combined ((NPK)Cl+M) treatment.(2) Waterlogging incubation method proposed by Warning was used to investigate N mineralization characteristic. Nitrogen accumulations were significantly improved under the chemical fertilizer or organic fertilizer, the highest nitrogen accumulations appeared in the1.5NPK+M treatment and those in the CK treatment was relatively low. N supplying intensity was lower and faster in the single applying N, and N supplying intensity was relatively high and short in the unbalanced fertilization treatments. Nitrogen accumulations and nitrogen mineralization potential (No) were significantly improved under combined application of organic manure and inorganic NPK, But the increasing extent of chloride-containing fertilizer and organic manure combined was much lower than the fertilization of organic manure and inorganic NPK. Ratio of N mineralization potential to soil total N in the N, NP and NPK treatments were significantly lower than CK, and combined application of organic manure and inorganic NPK was highest. In short, long-term fertilization of organie and inorganie is considered the best way for maintaining the soil fertility. It can affect soil N minerlization potential, in order to improve the capacity of soil N supplying. Therefore, we should attach importance to applying organic manure in agricultural production and pay attention to the combination of organic manure and inorganic fertilizer.(3) The abundance of ammonia-oxidizing microorganisms in neutral purple soil were studied by Real-time PCR. Results showed that the amoA gene copy numbers of ammonia-oxidizing archaea (AOA) was obviously higher than that of ammonia-oxidizing bacteria (AOB) in neutral purple soil. The highest population sizes of AOB appeared in the1.5NPK+M treatment and those in the (NPK)Cl+M treatment was relatively low. Phosphorus is one of the most important elements to affect the abundance of AOB. Quantitative data showed that the trends of AOB abundance changed significantly than AOA in different fertilization treatments. The results obtained show that AOA is a potential population and may have a potential capacity for ammonia oxidation.(4) Soil bacterial community structure was analyzed by T-RFLP. The results showed that higher diversity of the soil AOB community was found in organic manure and inorganic NPK treatment and those in the (NPK)Cl+M treatment was relatively low. The soil ammonia-oxidizing archaea amoA gene libraries changed less. The significantly higher diversity of the soil AOA community was recorded in the (NPK)Cl+M treatment, while the lowest in the M treatment. The proportion of dominant fungi genera appeared as high as82.81%. It was speculated that the soil ammonia-oxidizing bacterial amoA gene libraries are influenced by different fertilization very much, and which had mild effect on the AOA community.(5) The nitrification in neutral purple soil was studied by chemical analysis. Compared to CK, long-term application of nitrogen and phosphate fertilizer could significantly improve the total number of soil nitrobacteria, especially organic manure and inorganic NPK fertilizer combined application and those in the (NPK)Cl+M treatment was relatively low. The total nitrogen and effective phosphorus were positively related (P<0.05) to the total number of soil nitrobacteria. The significantly higher PNR was recorded in the NPK+M treatment, while the lowest in the (NPK)ci+M treatment. The soil pH and effective phosphorus affected significantly the potential nitrification rate, with a correlation coefficient of r=0.724(P<0.05) and r=0.698(P<0.05). The nitrification intensity and PNR had essentially the same changing tendency.(6) The total number of soil nitrobacteria, potential nitrification rate and nitrification intensity of CK treatment soils were examined after applying NaH2PO4·H2O fertilizer for75days. The total number of soil nitrobacteria was a decreased tendency as the concentration of phosphate was increasing. Significant differences of the potential nitrification rate was found between different treatments. In a range of0-50mg P2O5·kg-1soil, the potential nitrification rate increased too along with the phosphate concentration increase. After that, the potential nitrification rate decreases by the phosphate concentration increase. The nitrification intensity of soil was inconsistent with the change trend of the total number of soil nitrobacteria and potential nitrification rate. Different concentration of phosphate treatments might have mild effect on the nitrification intensity of soil. |
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