Genesis of humus B horizons in hydromorphic humus podzols
Genesis of humus B horizons in hydromorphic humus podzols
复制标题
水形腐殖质灰化土中腐殖质 B 层的成因
作者：
V. Farmer;J. Skjemstad;C. Thompson
在亚热带和热带沿海平原的石英砂的地下水位顶部，形成了一种独特的灰泥B层，其特征是腐殖质积聚，铁含量低，外观和成分横向均匀，经常发生硬胶结。具有这种B层的土壤在许多分类上与自由排水的灰化土分开，如地下水灰化土1、腐殖质灰化土2、水态腐殖质灰化土3、水系灰化土和土系灰化土4，因为它们具有独特的形态和可能的成因差异。然而，虽然富含腐殖质的B层（Bh）与地下水位之间的联系早已被认识到，但对Bh层形成模式的大多数解释基本上与自由排水灰土中的Bhir（富含铁的Bh）层相似。这些并不能提供一个令人满意的解释机制，即有机物质是在一个几乎没有阶地氧化物的环境中沉淀下来的。我们认为，这样的Bh层可能是富有机物地表水和地下水中的铝在B层共沉淀的结果。此外，这种机制还可能导致有机胶结硬岩的形成，通常被称为咖啡岩，在温带和热带地区，这种硬岩经常与水态灰化岩联系在一起。
A distinctive podzol B horizon, characterized by accumulated humus, low-iron content, lateral uniformity in appearance and composition and frequently hard cementation, develops at the top of the water table in quartz sands on coastal plains in the subtropics and tropics. Soils with such B horizons are separated from freely-drained podzols in many classifications, such as groundwater podzols1, humus podzols2, hydromorphic humic podzols3, aquods and humods4, because of a distinctive morphology and possible differences in genesis. However, while an association between the humus-rich B horizon (Bh) and the underlying water table has long been recognized, most explanations offered for the mode of formation of the Bh have been essentially similar to those for Bhir (iron-rich Bh) horizons in freely-drained podzols. These do not provide a satisfactory explanation of the mechanism whereby organic matter is precipitated in an environment that is virtually free of sesquidoxes. We suggest here that such Bh horizons may form as the result of coprecipitation in the B horizon between organic-rich surface waters and aluminium from the groundwater. Further, such a mechanism can lead to the development of organic-cemented hardpans, commonly called coffee rock3,5, that are so frequently associated with hydromorphic podzols in both temperate and tropical regions3.