【目的】分析东北黑土区旱田改稻田后土壤有机碳、全氮含量及其密度和~(13)C、~(15)N自然丰度值的动态变化,探讨旱田改稻田后土壤有机碳(氮)的固定能力及其稳定性,揭示旱田改稻田后土壤有机碳(氮)的演变规律,为东北黑土的合理利用和培肥提供理论依据。【方法】结合野外实地调查,选择典型黑土区旱田土壤(种植大豆年限大于60年)和改种不同年限的稻田土壤(3、5、10、17、20和25年,旱田改稻田前种植历史基本相同,均为大豆),利用稳定同位素分析技术,研究旱田改稻田后土壤有机碳、全氮的动态变化特征。【结果】旱田改稻田25年间,在0—60 cm土层,土壤有机碳和全氮含量的变化趋势均表现为:在改种的前3年迅速下降,降幅分别为13.60%—43.27%和10.40%—40.60%,在3—25年间随改种年限延长呈逐渐增加的趋势,且在20—60 cm土层出现累积,但在3—5年期间增加幅度较大,在5—25年期间增加较为缓慢,在改种17—25年期间,稻田土壤有机碳和全氮含量均高于旱田土壤;0—60 cm土层土壤有机碳和全氮密度的变化趋势与其含量的变化趋势大致相同,在改种的3年间0—60 cm土层土壤有机碳和全氮密度分别降低了26.53%和21.89%,在改种5—25年间0—60 cm土层稻田土壤有机碳和全氮密度均大于旱田土壤,增幅分别为9.87%—21.48%和10.2%—19.3%;旱田改稻田后,土壤全氮与有机碳的变化密切相关,土壤全氮与有机碳的含量、密度之间均呈显著线性正相关关系(P<0.01)。在0—60 cm土层,土壤δ~(13)C值在改种的3年间明显上升,在3—25年间随改种年限延长呈逐渐下降趋势,且大于5年的稻田土壤δ~(13)C值均低于旱田土壤,而土壤δ~(15)N值在改种的25年间随改种年限延长呈逐年下降趋势,各年限稻田土壤δ~(15)N值均低于旱田土壤,相同年限土壤的δ~(13)C值和δ~(15)N值均随着土层加深而增大;0—40 cm土层土壤δ~(13)C值与土壤有机碳含量之间呈显著线性负相关关系(P<0.01),但各土层土壤δ~(15)N值与土壤全氮含量之间则无显著相关性。【结论】东北黑土区旱田改稻田大于5年后,稻田土壤具有明显的固碳(氮)能力,稳定性碳(氮)在20—60 cm土层累积;改种稻田年限小于5年,应注重有机碳(氮)的补充,以维持和提高土壤有机碳(氮)水平。 【Objective】 The objective of this study was to analyze the dynamic changes of soil organic carbon, total nitrogen, its density and natural abundance of ~ (13) C, ~ (15) N in a paddy field in the northeastern black soil area, Nitrogen) fixation ability and its stability, revealing the evolution of soil organic carbon (N) after the paddy field modified dry farming to provide a theoretical basis for the rational use and fertilization of black soil in Northeast China. 【Method】 Combining with the field investigation, we selected the dry soil of typical black soil area (the soybean growing season was more than 60 years) and the paddy soil of different years (3,5,10,17,20 and 25 years) Basically the same, are soybeans), the use of stable isotope analysis of dryland to study the dynamics of soil organic carbon and total nitrogen after the change characteristics. 【Result】 The trend of soil organic carbon and total nitrogen in 0-60 cm soil layer changed from paddy field to paddy field in 25 years. The change trend of soil organic carbon and total nitrogen decreased rapidly from 13.60% -43.27% 10.40% -40.60%. It shows a trend of increasing gradually with the extension of breeding years in 3 to 25 years and accumulating in 20-60 cm soil layer. However, it increases more in 3-5 years, and in 5-25 years During the period from 17 to 25 years, the contents of soil organic carbon and total nitrogen in paddy soil were higher than those in upland soil. The trend of soil organic carbon and total nitrogen in 0-60 cm soil layer and the change trend of soil total nitrogen content The density of soil organic carbon and total nitrogen in 0-60 cm soil layer decreased by 26.53% and 21.89% respectively in the three years of re-planting. The soil organic carbon and total nitrogen The soil total nitrogen was closely related to the change of organic carbon after the paddy field was reformed, and the content and density of soil total nitrogen and organic carbon were both higher than those of dryland soil, with the increment of 9.87% -21.48% and 10.2% -19.3% There was a significant linear positive correlation (P <0.01). In 0-60 cm soil layer, the δ ~ (13) C value of soil increased obviously during the three years of re-planting, and gradually decreased with the extension of years of rearing in 3-25 years, and the δ ~ (-) 13) C values ​​were lower than those in upland soil, and the δ ~ (15) N values ​​of the soil were declining year by year with the increasing years of replanting in the 25 years after replanting, and the values ​​of δ ~ (15) N in paddy soils were lower than those in upland fields The values ​​of δ ~ (13) C and δ ~ (15) N in soils and soils all increased with the deepening of soil depth. The values ​​of δ ~ (13) C in 0-40 cm soil layer and soil organic carbon (P <0.01). However, there was no significant correlation between δ ~ (15) N value and soil total nitrogen content in different soil layers. 【Conclusion】 The paddy field in the black soil region of northeastern China was over 5 years old. The paddy soil had obvious carbon sequestration and nitrogen fixation ability. Soil carbon in 20-60 cm soil layer accumulated in paddy field. Focus on organic carbon (nitrogen) supplementation to maintain and increase soil organic carbon (nitrogen) levels.