黄土高原不同类型土壤团聚体中氮库分布的研究

【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。

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

According to both different types of vegetation and types of soil, we collected twenty-two soil samples from different regions of the Loess Plateau in order to investigate the distribution of the soil nitrogen in different kinds of soil aggregates. 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 the kinds of soil aggregates. The content of organic nitrogen was different in various kinds of soil aggregates, and the content of organic nitrogen appear the shape of a“∧”with the kinds of soil aggregates from >5mm to <0.25mm, there was a peak value at the soil aggregate of 0.25~1mm. There are not obvious distribution pattern of the content of mineral nitrogen, ammonium nitrogen and nitrate nitrogen in different kinds of soil aggregates. The nitrogen stockpiling quantity distribution in different kinds of soil aggregates appear the shape of a“∨”, no matter organic nitrogen, mineral nitrogen, ammonium nitrogen and nitrate nitrogen. The content of nitrogen of every kind of soil aggregate decreases with the increase of latitude in the Loess Plateau, Eum-Orthic Anthrosols is the highest and Ust-Sandiic Entisols is the lowest. Although the content and stockpiling quantity of nitrogen was different in various types of vegetation, there was a same trend, which was: natural forest land >bare land> artificial forest land>farming land.