三江源区土地利用方式对土壤氮素特征的影响

以三江源区曲麻莱县高寒草甸草原、退化高寒草甸草原、退化高寒草原和人工草地4种土地利用方式为研究对象,研究了不同土地利用方式的土壤全氮、有效氮、铵态氮、硝态氮、无机氮总量及比例,结果表明:4种利用方式土壤的氮素含量均处于较低水平,在0~10 cm土层,土壤全氮与有效氮含量表现出相似的规律性,人工草地最高,退化高寒草甸草原最低。与高寒草甸草原相比,退化高寒草甸草原0~10 cm土层全氮和有效氮含量分别降低了52.4%和76.2%,而10~40 cm土层的全氮和有效氮含量却明显增加。对土壤铵态氮和硝态氮含量的研究结果进一步表明,研究区域土壤中无机氮以硝态氮为主,退化导致0~10 cm土层的铵态氮和硝态氮含量降低,退化和人工种植均导致0~10 cm土层硝态氮含量明显降低,而10~20 cm和20~40 cm土层的硝态氮含量明显升高,且这两个土层之间差异不显著,40~60 cm土层又明显降低。因此,退化和人工种植均导致土壤硝态氮沿土壤剖面淋溶下移,并且淋溶主要发生在0~40 cm深度的土壤中。土壤无机氮总量与硝态氮表现出相似的规律性,对土壤无机氮总量和比例的研究也表明退化加剧了土壤氮素的矿化过程。

Effect of land use patterns on soil nitrogen characteristics in Three-river Headwater Area

Four land use pattems,i.e.,alpine meadow steppe,degraded alpine meadow steppe,degraded alpine steppe and artificial grassland,were selected to study effect of land use patterns on the soil nitrogen characteristics.Soil total nitrogen,available nitrogen,ammonium nitrogen,nitrate nitrogen,total inorganic nitrogen (TIN) and its percentage were determined.The results showed that soil nitrogen content of four land use types were all at a lower level.Soil total and available nitrogen of four land use patterns changed similarly in 0 ～ 10 cm soil depth,and the artificial grassland was the highest,the degraded alpine meadow steppe was the lowest.Soil total and available nitrogen in 0 ～ 10 cm soil depth for the degraded alpine meadow steppe decreased 52.4％ and 76.2％ respectively,but those in 10 ～ 40 cm soil increased significantly compared with the alpine meadow steppe.The results of soil ammonium and nitrate nitrogen showed that nitrate nitrogen was the main inorganic nitrogen in soil.Degradation caused both ammonium nitrogen and nitrate nitrogen in 0 ～ 10 cm soil depth decreasing.Both degradation and artificial planting caused nitrate nitrogen decreased in 0 ～ 10 cm soil depth,but increased in 10 ～ 20 cm and 20 ～ 40 cm soil depth,and there was no significant difference between the two soil depth,while soil nitrate nitrogen decreased in 40 ～ 60 cm soil depth.There were no significant differences for both ammonium nitrogen and nitrate nitrogen in 40 ～ 60 cm soil among four land use patterns.Therefore,both degradation and artificial planting caused nitrate nitrogen leaching down in soil profile,and the leaching mainly happened in 0 ～ 40 cm soil depth.Soil total inorganic nitrogen showed a similar trend with soil nitrate nitrogen.The results of total inorganic nitrogen content and the percentage showed that degradation process increased soil nitrogen mineralization.