西藏酸性土壤的酸度特征

ACIDITY OF ACID SOILS IN TIBET

根据西藏7个土类6 6个土壤剖面2 5 7层土样的分析资料,探讨酸性土的酸度特征。西藏酸性土面积约占1/ 5 ,主要为山地湿润森林型和高山灌丛草甸型土壤,集中分布于藏东南地区。土壤pH主要决定于其潜性酸中的交换性酸,特别是其中占优势的交换性Al3 + ,而受非交换性酸的影响较小。交换性酸中Al3 + 的相对比例随交换性酸总量增加而增大,随有机质增加而减小,H+ 的相对比例则呈相反的变化。非交换性酸主要来源于有机质(腐殖质酸性功能团缔合H和络合Al的解离)。土壤pH与交换性酸、非交换性酸饱和度分别呈近线性、非线性负相关,而与盐基饱和度呈非线性正相关,且主要受优势的交换性Ca2 +制约。

Based on the analytic data of soil samples collected from 257 soil layers of 66 soil profiles under 7 soil types in Tibet, characteristics of the acidity of the acid soils were explored. Acid soils, accounting for one fifth of the total land area of Tibet,are mainly distributed in the southeast of Tibet, under the vegetation of mountain humid forests and alpine shrubby meadows. Soil pH is determined mainly by exchangeable acid in potential acid, especially, exchangeable Al 3+ , which is in dominancy, while non exchangeable acid has less impact on that. The proportion of exchangeable Al 3+ increases with the increase in exchangeable acid, but decreases with the increase in OM. However, the relative proportion of exchangeable H + shows a reverse trend Non exchangeable acid comes mainly from OM (through disassociation of H and Al from humic acidic functional groups).Soil pH is in near linear negative correlation with the saturation of exchangeable acid and in non linear one with the saturation of nonexchangeable acid, but in nonlinear positive correlation with base saturation, which is mainly restrained by the dominant exchangeable base Ca 2+ .