| Studying nitrogen (N) fertility and N supply characteristics in soils plays an important role in the rational utilization of soil N resource and reducing the use of N fertilizer. Paddy soils deriving from three types of parent materials and from three cropping systems were selected to investigate the N fertility characteristics in Changsha county, Hunan. N mineralization dynamic model proposed by International Rice Research Institute was used to forecast the N supplying capacity of paddy soil. A long-term simulating experiment was conducted to investigate the effect of fertilization and groundwater levels on organic N fraction and N mineralization characteristic, so as to reveal the dynamics of characteristics and the factors influencing N mineralization in paddy soil. The main results are summarized as follows.Soil total N was0.60～1.50g·kg-1and alkaline hydrolytic N was84.10～182.70mg·kg-1. Acid hydrolysable N accounted for62.7%～82.63%of total N and non-acid hydrolysis N accounted for17.4%～37.3%of total N. The order of organic N fractions was hydrolysable unidentified N, amino acid N, ammonium N, amino sugar N. And the types of parent materials had significant effect on amino acid N content (p<0.05), the order of amino acid N content is the quaternary red clay, granite weathered material, river alluvium.At two weeks after waterflooded incubation, soil mineralizable N varied from24.53～84.61mg·kg-1. There were significantly positive correlations between soil mineralizable N and total N and alkaline hydrolytic N, with the coefficients of correlation of0.492and0.535, respectively. Cropping system had significant effect on soil mineralization N (p<0.05), and the order of soil mineralization N content was rice field-upland field rotation, double cropping rice, rice field to upland field for3-5years.Soil mineralizable N potential (N0) and mineralization rate constant (c) were65.70～170.09mg·kg-1and0.0083～0.0386, respectively, and the amount of soil N supply was112.51～422.10kg/hm2and N supply rate was7.07%-23.53%.A long-term simulating experiment showed that the content of acid hydrolysable N in organic manure treatments were significantly higher than those of inorganic manure treatments, and the content of acid hydrolysable N in low groundwater level treatments was slightly higher than those of high groundwater level treatments.The waterlogging incubation experiment with constant temperature for106days showed that the mineralization N accumulation reached maximum value in different treatments at88day after the waterlogging incubation. The order of accumulation mineralization N was low groundwater level with constant organic manure (DCY), low groundwater level with high quantity organic manure (DGY), high groundwater level with constant organic manure (GCY), high groundwater level with high quantity organic manure (GGY), low groundwater level with inorganic manure (DH) and high groundwater level with inorganic manure (GH). At106d after the waterlogging incubation, the content hydrolysable unidentified N was greatly reduced, followed by amino acid N and ammonium N, but the contents of non-acid hydrolysis N and amino sugar N were increased. The correlation coefficients between the mineralizable N potential (N0) and hydrolysable unidentified N, amino acid N, ammonium N were0.865,0.727and0.643, respectively. And the order of soil urease activity in difference treatments was DCY>DGY>GCY>GGY>DH>GH. In addition, the activities of soil invertase and catalase in organic fertilizer treatments were higher than those of the inorganic manure treatments. |
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