The Physical and Chemical Properties of the Gray Hydromorphic Soils of the Hawaiian Islands
1974
Hussain, M. S. | Swindale, L. D.
Gray hydromorphics, a heterogeneous group of soils of the Hawaiian Islands, have developed some common characteristics during pedogenesis under impeded drainage. These soils are characterized by their poor physical properties, high moisture-holding capacity, and high clay content. The mean clay/15-bar moisture ratio is 2.56. Under the gleization process of soil formation, free iron and free manganese were found to be concentrated near the surface and above the fluctuating groundwater table. A net loss of these elements was observed from the soil profiles. The gray hydromorphic soils were found to constitute a typical hydrologic sequence. The SiO₂/R₂O₃ and SiO₂/Al₂O₃ ratios of the soils increased with increasing degree of hydromorphism. The SiO₂/R₂O₃ and SiO₂/Al₂O₃ ratios in the fine clay fractions of the soils increased with increasing drainage impedance. Al₂O₃/Fe₂O₃ ratios in the fine clays of these soils decreased with increasing degree of hydromorphism and increasing percentage of montmorillonite. Conditions of poor drainage maintained a ferrous ion activity in the soil solution sufficient to allow increasing formation of iron-rich montmorillonite clays.
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