西藏土壤有效铁含量及其影响因素

根据西藏土壤18个供试土类169个剖面有效铁(Fe)的分析资料,探讨土壤有效Fe含量变化及其影响因素。结果表明,西藏供试土壤表层有效Fe含量平均为83 mg/kg,但各类土壤变化很大,其中50~238 mg/kg的土壤面积占35.2%,<50 mg/kg的土壤面积占61.5%,只有少部分土壤有效Fe低于缺乏临界值5 mg/kg。有效Fe高的土壤几乎都是有机质丰富的酸性土,而有效Fe较低的土壤大多是有机质缺乏的碱性钙质土。土壤有效Fe含量受pH、铁的形态、有机质和粘粒等因素的综合影响。土壤有效Fe随pH的升高而降低。土壤有效Fe与全Fe、游离Fe无关,而与活性Fe、络合Fe呈极显著正相关,据此推论有效Fe来自活性Fe包括其中络合Fe与非络合活性Fe两部分。土壤有效Fe与有机质、粘粒含量呈极显著正相关,有机质对有效Fe的贡献在于其作为络合剂形成络合Fe和作为阳离子吸附载体吸持活性Fe离子;粘粒的贡献则是作为阳离子吸附载体吸持活性Fe离子,但其贡献远不如有机质。

Status of Soil Available Iron and Its Affecting Factors in Tibet

According to the analysis data of 695 soil samples from 169 soils profiles of 18 soils types,soil available iron(A-Fe) and its affecting factors were studied.The average content of soil available iron,tested in surface soil horizon of Tibet,is 83 mg/kg,with large variance in different soil types.The area of the soils,of which the contents of soil available iron is at 50~238 mg/kg,accounts for 35.2% of Tibet soil area,and the area of the soils under 50 mg/kg accounts for 61.5%,and only a little part of soils is under the critic value of 5 mg/kg.The soil with high contents of A-Fe is almost all of the acid soil which is rich in soil organic matter(SOM).On the contrary,the soils in low A-Fe are most of the alkalescent calcareous soil which is lack of SOM.Soil A-Fe is influenced by different ingredients simultaneously,such as pH,types of iron,SOM,Clay,etc.A-Fe content rises up with the pH falling down,and has significant positive correlation with both soil active iron and soil complex iron,but has no correlation with soil total iron and soil free iron.According to this,soil available iron comes from active iron,including complex and free active iron.Soil A-Fe has significant positive correlation with SOM and Clay.The contribution of SOM to A-Fe is due to that SOM forms soil chelated iron as a complexing agent and absorbs active Fe ion as a carrier of cation,whereas the contribution of Clay to A-Fe is far from SOM,only due to that it absorbs active Fe ion as a carrier of cation.