贝加尔针茅草原土壤无机氮含量对氮素添加的响应

土壤无机氮是可以直接被植物根系吸收的氮素形态,也是表征土壤肥力的重要参数。基于内蒙古贝加尔针茅草原长期氮素添加(NH4NO3)试验平台,本研究选取4个氮素添加水平,分别是0(CK)、30(N30)、50(N50)和100 kg N·hm-2·a-1(N100),探究氮素添加对土壤无机氮的影响。于2015年生长季(6—10月)每月中旬分别采集0~10、10~20、20~30、30~40 cm四个土层深度的土壤样品,测定土壤铵态氮(NH+4-N)和硝态氮(NO-3-N)含量。结果表明:贝加尔针茅草原0~40 cm土壤中,CK、N30和N50处理的土壤铵态氮含量较土壤硝态氮含量高,N100处理中,二者几乎各占一半,生长季内无机氮含量的变化趋势与硝态氮一致;各处理土壤铵态氮、硝态氮和无机氮含量在土层间的关系均表现为:0~1010~2020~3030~40 cm,且都随氮素添加水平增加而增加。经方差分析表明,氮素添加、取样时间、土层深度及三者交互作用对土壤铵态氮、硝态氮和无机氮含量均有极显著影响;本试验中,在自然水热条件下,N100处理有明显的硝态氮累积,达"氮饱和点"。

Responses of Soil Inorganic Nitrogen Content to Nitrogen Addition in the Stipa baicalensis Grassland of Inner Mongolia

Soil inorganic nitrogen is a nitrogen form which can be absorbed by plant roots directly, and it is an important representative parameter of soil fertility.We have been carrying out a nitrogen addition test in Stipa baicalensis grassland in Inner Mongolia from 2010.Four nitrogen addition treatments were selected, namelyCK (0 kg N · hm 2 · a-1), N30(30 kg N· hm-2 · a-1), N50(50 kg N· hm-2 · a-1) and N100(100 kg N · hm-2 · a-1), to explore the effect of nitrogen addition on soil inorganic nitrogen.Soil samples were collected in the middle of each month during the growing season (June to October) in 2015,and the sampling depth was 40 cm.The content of ammonium nitrogen and nitrate nitrogen were determined.The results showed that:From 0 to 40 cm soil layers of Stipa baicalensis steppe, the content of soil ammonium nitrogen were higher than soil nitrate nitrogen's in CK, N30 and N50 treatment, but half and half in N100 treatment, and the variation tendency of inorganic nitrogen content was consistent with nitrate nitrogen in the growing season;The contents of soil ammonium nitrogen, nitrate nitrogen and inorganic nitrogen increased within the increase of nitrogen addition, however, decreased along with deepening the soil layer.The analysis of variance showed that nitrogen addition, sampling time, soil layer and their interactions had significant impact on the soil ammonium nitrogen, nitrate nitrogen and inorganic nitrogen content.The accumulation of nitrate nitrogenre was obviously in N100 treatment, so N100 had reached the“nitrogen saturation point”in the present study under the natural hydrothermal conditions.