长江三角洲典型区农田土壤碳氮比值的演变趋势及其环境意义

Spatial and Temporal Variation of C/N Ratios of Agricultural Soils in Typical Area of Yangtze Delta Region and its Environmental Significance

土壤碳氮比值（C/N）是衡量土壤C、N营养平衡状况的指标，它的演变趋势对土壤碳、氮循环有重要影响。本文通过野外调查、采样和分析，运用地统计学方法和GIS技术，分析了张家港市自1980～2004年土壤C/N值的时空演变及其对土壤碳、氮循环的意义。结果表明，张家港市土壤有机质和全氮总体上明显提高，土壤C/N值也发生了不同程度的变异，主要表现在南部的人为土区土壤C/N降低，其中普通铁聚水耕人为土降低显著（p〈0．001），平均降低0．85个单位，北部雏形土区C/N亦呈降低趋势，但无显著性（p〉0．05）。在土壤有机质和全氮提高的同时，C/N的降低提高了微生物活性，加快有机质和有机氮的分解矿化，土壤固定有机碳能力降低，并释放更多的无机氮，氮素流失的可能性增加，对环境产生负面影响。今后的农业生产中应注意提高土壤碳素投入和降低氮素投入，如大力推行秸秆还田、增施有机肥、减少无机氮肥，以保持土壤碳氮平衡及土壤的可持续利用。

The C/N ratio of soils is an indicator for assessing C and N nutrition balance of soils. Its variation is significant in reflecting the carbon and nitrogen cycling of soils. Based on field investigation, sample collection and analysis, and application of statistics and GIS technology, this study has discussed the spatial and temporal variation of C/ N ratios and its effect on the C and N cycling in soil samples collected from the Zhangjiagang City from 1980 to 2004. The results indicated that the contents of soil organic matter （SOM） and soil total nitrogen （STN） are significantly increased in soils collected from 1980 to 2004,with a significant decrease of C/N ratios （p〈0. 001）for the Anthrosols in the southern of the city,especially average 0.85 units decrease for the Fe-accumuli-Anthrosols, and an unobvious decrease of C/N ratios （p〉0. 05） for the Cambosols in the northern of the city. With the increase of SOM and STN, the decrease of the C/N ratio resulted in the enhancing activity of the microbes, accelerating the rate of decomposition and mineralization of the SOM and STN,reducing the organic carbon fixation capacity of soils, releasing more inorganic N from soils,and influencing negatively on the environment. It is suggested that the input of more C and less N into soils, such as incorporating crop residues into soil, inputting less inorganic N fertilizers but more more organic fertilizers into soils for future farming practices, could effectively maintain the balance of the SOM and STN for sustainable utilization of soils.