Characteristics of Some Brown Grumusols of Arizona
1962
Johnson, W. M. | Cady, J. G. | James, M. S.
Extensive areas of well-drained brown Grumusols developed from weathered ultrabasic volcanic rocks exist in north-central and eastern Arizona. They are on nearly level to rolling topography under grass; precipitation ranges from < 10 to > 20 inches annually. They have clay profiles of nearly uniform brown color; moderately low organic matter content; very high base status; dominance of montmorillonite in the clay fractions; and evidence of much internal soil movement, namely: numerous slickensides, very gradual decrease of organic matter with depth, and diffuse or gradual and wavy horizon boundaries. Mineralogical studies indicate that in these soils the course of weathering of the rock and the nature of the weathering products are determined early and remain constant; montmorillonite is the dominant clay mineral in all horizons including the weathered material adjacent to the fresh rock. Comparisons are given with associated dark gray, poorly-drained Grumusols and with dark brown soils having textural B horizons that formed under timber-grass vegetation.
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