黄土高原不同类型土壤团聚体中氮库分布的研究

Distribution of Nitrogen Pools in Different Sizes of Loess Plateau Soil Aggregates

【目的】研究黄土高原主要土壤不同团聚体中氮库的分布特征。【方法】根据不同植被类型和土壤类型,分别从黄土高原不同地域分层(0～20、20～40和40～60 cm)采集22个土壤剖面样品。【结果】无论哪种团聚体,从表层向下,有机氮、矿质氮、铵态氮、硝态氮含量皆呈递减趋势。不同土壤团聚体,其有机氮含量明显不同,>5 mm、2～5 mm、1～2 mm、0.25～1 mm粒级团聚体有机氮含量依次递增趋势,而0.25～1 mm、<0.25 mm粒级团聚体的有机氮含量依次呈下降趋势,以0.25～1 mm团聚体有机氮含量最大;不同团聚体中铵态氮、硝态氮和矿质氮含量分布没有明显的规律性。由于不同大小团聚体所占比例不同,因此无论是土壤有机氮,还是矿物态氮,其贮量在土壤团聚体中的分布与含量并不完全一致:>5 mm、2～5 mm、1～2 mm粒级结构体中贮量依次呈递减趋势,而1～2 mm、0.25～1 mm、<0.25 mm依次呈递增趋势,以1～2 mm结构体贮量最低。【结论】在黄土高原地区,土壤中各级团聚体含氮量分布随纬度增加而降低,土垫旱耕人为土各级团聚体含氮量最高,干润砂质新成土各级团聚体含氮量最低。植被对团聚体中的氮素分布也存在一定影响,有机氮和矿质氮大体上均呈自然林地>新垦农田>人工林>农地。

[Objective ] The nitrogen content of soil aggregates is an important index for assessing the quality of soil structure. Therefore, we investigated the distribution of soil nitrogen pool for a large range size of soil aggregates in this study. [Method] In terms of the types of vegetation and soil, 22 soil samples from different profile （0-20 cm, 20-40 cm and 40-60 cm）were collected from different regions on the Loess Plateau. [ Result] The results indicated that the content of organic nitrogen, mineral nitrogen, ammonium nitrogen and nitrate nitrogen had a descending tendency with the depth of soil layer, no matter what size of soil aggregate. The content of organic nitrogen differed with various kinds of soil aggregates, for each soil layer, the organic nitrogen content increased in the order of 〉 5 mm, 2-5 mm, 1-2 mm, and 0.25-1 mm, and decreased from 0.25-1 mm to 〈 0.25 mm. There was no obvious distribution pattern for the content of mineral nitrogen, ammonium nitrogen and nitrate nitrogen from the size of soil aggregate perspective. Because of the different proportions of each size of soil aggregates, the nitrogen stockpiling quantity （including organic nitrogen, mineral nitrogen, ammonium nitrogen, and nitrate nitrogen） and content in different sizes of soil aggregates variedlt decreased following the sequence of 〉 5 mm, 2-5 mm, and 1-2 mm, and it increased in the order of 1-2 mm, 0.25-1 mm and 〈 0.25 mm. [Conclusion] The nitrogen content of each kind of soil aggregate decreased with increased latitude on the Loess Plateau. Also, the nitrogen content largely varied with soil, among which Eum-Orthic Anthrosols was the highest and Ust-Sandiic Entisols was the lowest. Vegetation had a large influence on the content and stockpiling quantity of nitrogen, for both organic nitrogen and mineral nitrogen, they showed natural forest land〉fresh assart〉artificial forest land〉farming land, on the whole.