A quantitative soil development index based on field morphologic data has been applied to a chronosequence of six soils at Honcut Creek in central California. The soils range from 600 yr to 1.6 m.y. in age and exist in a xeric-thermic soil climatic regime. Plots of the development of individual properties versus the log of soil age are generally linear. Of the eight soil properties used in the index, clay films, texture plus wet consistence, structure, and rubification (color hue and chroma), are most highly correlated with soil age (correlation coefficients for linenar regression of 0.96-0.87). Dry consistence, moist consistence, melanization (color value), and pH lowering are not as highly correlated with soil age (correlation coefficients of 0.68-0.55), although correlation coefficients for all eight soil properties are significant at α = 0.01 or 0.05 level. Depth functions of a horizon index that incorporates all eight soil properties chart the development of the A-horizons in Holocene soils and the development of the cambic and then argillic horizons in older soils. Total depth of soil development increases from about 60 cm in Holocene soils to more than 5 m in the oldest soils. Lithologic discontinuities and stratification are brought out in the horizon index because of their effects on soil development. Soils on the alluvial terraces of Honcut Creek have developed systematically over the 1.6 m.y. age span of the chronosequence: correlation coefficients for regressions of the profile index versus the log of soil age are ≥0.97 (significant at α = 0.01 level). The coefficient of variation of replicate profiles decreases with increasing soil age. The soil development index substantiates the geologic and pedologic correlations made during geologic mapping and soil survey of the area, although differences among soils in parent material and topographic factors complicate the age trends. © 1987.
Busacca, A. J. (1987). Pedogenesis of a chronosequence in the Sacramento Valley, California, U.S.A., I. Application of a soil development index. Geoderma, 41(1–2), 123–148. https://doi.org/10.1016/0016-7061(87)90032-2