Soil Moisture and Redoximorphic Features: A Historical Perspective
- P. L. M. Veneman,
- L. A. Spokas and
- D. L. Lindbo
This chapter focuses on soil micromorphological features and other soil characteristics associated with particular soil moisture regimes. It provides a comprehensive review of the leading research papers published mainly in the USA during the past 40 to 50 yr. We distinguished the following three periods of research activity: (i) Early Period, (ii) Middle Period, and (iii) the Present Period. Papers published in the Early Period focused often on a qualitative description of hydromorphic soil properties. The Middle Period is characterized by quantitative data collection, including determination of water table levels, redox potentials, soil water potentials, soil temperatures, and soil/water O2 levels. Research during the Present Period focuses on hydric soil formation and questions related to aquic moisture conditions. In addition, during this period flownet analysis was initiated to explain pedological processes on a whole landscape basis. Long-term saturation and chemical reduction are generally reflected in redox depletions as indicated by low-chroma colors. Lack of a C source, low temperatures, or aerated groundwater may result in failure to develop depletion features. Lithochromic parent materials (red Triassic beds, hematitic soils, carboniferous, and gray-colored soils) also are limiting the development of redoximorphic features, in particular iron- and manganese-depletions. Some soils lacking redoximorphic features may be saturated for prolonged periods of time. Well-drained soils may have short (≤2 wk) periods of saturation during the nongrowing season. Sometimes such an oxyaquic regime is evident by high chroma Fe concentrations and a high chroma matrix (≥4). Occasionally, redoximorphic features are unrelated to the present moisture regime and should be considered relic. Mottles also may form in stratified soils at the interface between the fine-textured and the underlaying coarse-textured sediments. These types of redoximorphic features generally are not indicative of true aquic conditions. The concept of soil drainage classes, while useful for agricultural purposes, is less suited to other uses where a more accurate assessment of the duration and frequency of saturation periods is required. For purposes of hydric soil assessment and aquic moisture regime characterization, use of a single parameter to indicate seasonal wetness is more error-prone than application of multiple indicators. Landscape position and associated hydrology strongly affect development of pedological features. Soils in lower landscape positions tend to have low hydraulic gradients and are saturated and reduced for prolonged periods. Soils developed in deep, sandy sediments are rarely saturated within the solum, except in low areas where the phreatic surface is within the upper portion of the soil profile.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
Copyright © 1998. . Copyright © 1998 by the Soil Science Society of America, Inc., 5585 Guilford Rd., Madison, WI 53711 USA