东北黑土不同开垦年限稻田土壤有机氮矿化特征

目的]分析东北黑土自然荒地开垦种稻后土壤矿化氮含量、氮净矿化速率和氮净矿化率,探讨土壤供氮能力及其特点,揭示土壤氮素的演变规律,为东北黑土的合理利用和培肥提供理论依据.方法]以东北黑土自然荒地(0 a,为对照土壤,原始自然草甸植被)和不同开垦年限(12、35、62和85 a)的稻田(地形、种植制度、施肥和水分管理等...

Characteristics of Organic Nitrogen Mineralization in Paddy Soil with Different Reclamation Years in Black Soil of Northeast China

【Objective】 The aim of this study was to analyze the mineralized nitrogen (N) content, net N mineralized rate and net N mineralized ratio (the ratio of mineralized N to total N) in paddy soil with different reclamation years in black soil, and to explore the soil N supply capacity and its characteristics, and to reveal the soil N evolution law, so as to provide the theoretical basis for rational utilization and fertilization of black soil in Northeast China.【Method】 The natural wasteland (0 years, as the control soil, original natural meadow vegetation) and paddy soils with different reclamation years (12, 35, 62 and 85 a) (topography and cropping system, fertilization, and water management, roughly the same) in black soil region were selected as the research object, and the characteristics of soil organic N mineralization after cultivated rice form natural wasteland in black soil were studied by the water-logged incubation method.【Result】 During the early stages of incubation (about 1 month), the cumulative mineralized N increased rapidly in each year, then showed a slow increase trend. At the end of incubation (297 d), the cumulative mineralized N ranged from 212.43 to 388.11 mg·kg^-1, and the order of cumulative mineralized N was 0, 12, 35, 85 and 62 a. The mineralization process of soil organic N could be well described by a hybrid model (Special model), and the soil organic N pools could be divided into the increment N pool (the N pool made available after a drying and rewetting event) and the resistant N pool. Compared with the control soil (0 a), the potentially mineralisable N (N_F) of the increment N pool in all paddy soils showed a decreasing trend in each year. There was no significant difference between paddy soils of 12 and 35 years, as well as 62 and 85 years, but the N_F in paddy soils of 12 and 35 years were significantly higher than that of 62 and 85 years (P<0.05). The rate constant (k_F) of mineralization of the increment N pool in paddy soils all showed an upward trend, but there was no significant difference between k_F of all paddy soils in each year (P>0.05). Compared with the control soil (0 a), the rate constant (k₀) of mineralization of the resistant N pool in paddy soils of 12 and 35 years did not change significantly (P>0.05), but k₀ in 62 and 85 years decreased significantly (P<0.05). The net N mineralization rate of the soils in each year were the largest at 4 days of incubation, and then decreased gradually. At the end of water-logged incubation (297 d), the order of the soil net N mineralization rate was consistent with that of the cumulative mineralization N. The net N mineralized ratio was relatively high at the beginning of incubation, and then increased slowly. At the end of incubation (297 d), the net N mineralized ratio ranged from 78.60 to 101.82 mg·g^-1, and the order was 0, 35, 12, 85 and 62 a. Soil total N and C/N were important factors affecting the amount of mineralization N and the net N mineralization rate in paddy soils with different reclamation years (P<0.05). The sum of initial mineral N and N_F could be used to characterize the N supply capacity of paddy soil in rice growing season; compared with the control soil (0 a), the N supply capacity of paddy soil in each year decreased significantly (P<0.05), and the soils of 12 and 35 years were significantly higher than that of 62 and 85 years (P<0.05).【Conclusion】 During 85 years of rice cultivation from natural wasteland in black soil, the N supply capacity in paddy soil have declined, and the decline was significant after 35 years rice cultivation. Therefore, the improvement of soil organic matter content should be paid attention in the soil fertility cultivation in paddy fields.