Chemistry of Soil Profiles Indicates Recurring Patterns and Modes of Moisture Migration

Abstract

The hypothesis that patterns and modes of soil moisture migration can be interpreted from relationships between soluble sodium percentage (SSP) and total soluble cations (TSC) with depth in soil profiles is developed. Capillary migration of moisture during the soil drying process is more apt to leave a chemical imprint on soil profiles than the initial wetting process since it occurs last, and cations move in closer proximity to exchange surfaces. Soil profiles must be sampled in contiguous increments small enough to differentiate important variables. Each soil sample must be wetted exactly to saturation prior to extraction of soluble Ca, Mg, and Na for analysis. Both cation exchange and salt precipitation cause progressive losses of multivalent cations from solution as moisture moves through soil. Resulting increases in SSP indicate directions of moisture migration. Decreases in TSC accompanied by increases in SSP apparently result from movement in thin films in response to capillary tensions > 1 bar (salt sieving). Moisture migration in extremely thin films in response to high tensions at forward extremities of capillary migrations apparently produces increases in TSC values accompanied by increases in SSP values (salt precipitation).

Objectives, methods, and environment--Gila River Phreatophyte Project, Graham County, Arizona

“…Comparisons of soil-moisture stress and temperature gradients are used to evaluate differences in forces that move moisture either as liquid or vapor (Miller and otKrs, 1961). Differences in soluble sodium percentage ard total soluble cations with depth in each soil profile are used to define recurring patterns and modes of moisture migration (Miller and Ratzlaff, 1961;1965).…”