Micromorphology of Hydromorphic Soils: Applications for Soil Genesis and Land Evaluation

Abstract

Periodic or permanent saturation with water creates oxidizing and/or reducing conditions which have a profound impact on soil physical, chemical and biological processes and land-use. Micromorphological analyses are particularly useful to show the effects of natural soil processes on a microscale, as will be illustrated for both organic and mineral soils. Level areas all over the world with hydromorphic fluvial, marine, aeolian or peat soils are widely being used for crop production, often after applying various drainage techniques. Changes in soil forming processes affecting organic materials from a saturated to an unsaturated water regime are illustrated by a micromorphological analysis of a transect across a bog with an environmental climax change from a Hemist to a Folist. For mineral soils attention is paid to mineralogical changes after drainage in acid sulphate soils. Processes differ within very short distances illustrating the particular usefulness of micromorphology in undisturbed samples. Redox processes affecting iron and manganese compounds result in selective mobility leading to characteristic precipitation and leaching patterns as a result of water movement. Thus, surface-water and groundwater gley phenomena may be distinguished. Preferential movement of water along macropores, which often implies bypass of the major part of the soil matrix, can be deduced from natural mottling patterns or can be made visible by staining techniques. Quantitative land evaluation procedures increasingly require computer simulation modelling. Morphological data can be used to define realistic physical boundary conditions of natural flow systems in terms of the number and type of continuous flow pathways per unit cross-sectional area. © 1990.