黄土高原典型土壤有机氮组分剖面分布的变化特征

The Changing Characteristics of Profile Distribution of Soil Organic Nitrogen Component of the Typical Soil Types on the Loess Plateau

【目的】研究黄土高原主要典型区域不同土层土壤有机氮组分分布特征。【方法】根据土壤类型和土地利用方式,分别从黄土高原南北不同典型区域分层(0—10、10—20、20—40、40—60、60—80、80—100、100—120和120—140 cm)采集96个土壤样品,用Bremner法测定土壤有机氮组分含量。【结果】从北到南,土壤中有机氮及各组分含量呈增加趋势,各组分占酸解全氮的比例相对稳定,而酸解全氮占全氮比例在0—40 cm土呈下降趋势,40 cm以下土层趋于稳定;从南到北同层次、相同土地利用方式下有机氮各组分均表现为0—40 cm土层迅速下降,40—80 cm土层缓慢下降,80 cm以下土层基本稳定。不同土壤有机氮各组分在整个剖面上占酸解性全氮的平均比例不同,干润砂质新成土:酸解氨基酸态氮(39.5%)>酸解氨态氮(32.3%)>酸解未知态氮(25.7%)>酸解氨基糖态氮(2.5%);黄土正常新成土:酸解氨基酸态氮(36.0%)>酸解氨态氮(35.6%)>酸解未知态氮(25.3%)>酸解氨基糖态氮(3.1%);土垫旱耕人为土:酸解氨态氮(50.6%)>酸解氨基酸态氮(29.0%)>酸解未知态氮(17.5%)>酸解氨基糖态氮(2.8%)。供试土样中除氨基糖态氮外,草地土壤各有机氮组分在0—40 cm土层内均高于同层次的农田土壤,但随土层深度增加,差异性减小。【结论】黄土高原典型区域从北到南土壤各有机氮组分含量呈增加趋势,但在酸解全氮中的比例相对稳定,酸解性全氮占全氮比例呈下降趋势;酸解氨基酸态氮和氨态氮是研究区域最重要土壤有机氮形态;土地利用类型对土壤有机氮组分含量分布存在一定影响,基本呈草地>农田的分布规律。

【Objective】 In order to evaluate the effects of location,soil depth and land use on the contents of soil organic nitrogen（N）,the size and composition of soil organic N pool were studied using a large variety of soil profiles sampled on the Loess Plateau.【Method】 Based on different soil types and land-use patterns,96 soil samples in 8 depth classes（0-10,10-20,20-40,40-60,60-80,80-100,100-120 and 120-140 cm）were collected from different regions on the Loess Plateau.The method of Bremner was used to test the soil organic N content.【Result】Even with the same land use pattern,the content of soil depth-specific total soil hydrolysable N and its components increased from north to south on the Loess Plateau.The proportion of organic N components within total hydrolysable N was stable.However,the proportion of total hydrolysable N in total soil N significantly decreased within 0-40 cm layers and remained stable below 40 cm.The content of four components significantly decreased within 0-40 cm,slightly decreased within 40-80 cm and remained stable below 80 cm.The percentage of organic N components in total hydrolysable N differed among soil types： amino acid-N（39.5%）ammonia N（32.3%）HUN fraction（25.7%）amino sugar-N（2.5%） in Ust-Sandiic Entisols;amino acid-N（36.0%）ammonia N（35.6%）HUN fraction（25.3%）amino sugar-N（3.1%） in Los-Orthic-Entisol;and ammonia N（50.6%）amino acid-N（29.0%）HUN fraction（17.5%）amino sugar-N（2.8%） in Eum-Orthic Anthrosol.Except amino sugar-N,all the soil organic N components within 0-40 cm in grassland were more than those in cropland;however,the inter-layer variation became smaller with the profiles.【Conclusion】From north to south of the Loess Plateau,the content of organic N and its different forms increased,the proportion of organic N component in total hydrolysable N was stable in the same layer under the same land-use patterns.However,the proportion of total hydrolysable N in total soil N decreased.Amino acid-N and ammonia N were the major forms of the soil organic N on the Loess Plateau.Land-use pattern had a great effect on the content and distribution of N.Both organic N and its components in grassland was more than that in cropland.