COMBINED DAILY CLIMATIC DATA AND DILUTE SOLUTION CHEMISTRY IN STUDIES OF SOIL PROFILE FORMATION1

Abstract

A model was developed for converting long-time daily records of temperature and precipitation into daily depths of moistening and drying of the soil. The time-depth distributions of moist and dry zones were summed and converted to a prediction equation of the form, log F = k1 - k2 log D where F is the frequency of completed moist-dry cycles; D is depth, and k1 and k2 are constants characteristic of a particular soil and climate. The average annual amount of excess precipitation that fell when soil moisture was completely recharged completed the numerical description of the soil moisture regime. The depth that has a frequency of one completed moist-dry cycle per year coincides with the depth of solum in Missouri soils. It appears that the upper boundary of the B horizon is determined by the average depth of penetration of summer rains. Estimated amounts of water passing planes in the soil can be summed by integration of the prediction equation for depth-frequency of completed moist-dry cycles. Analyses of soil solutions produced when dry soil samples were equilibrated with water for one week suggest that alumino-silicate minerals react in a manner that is predicted by chemical thermodynamics. Kaolinite appears to be the stable clay mineral in a wide array of soil horizons including those with large amounts of montmorillonite. Quartz appears to be instable in some A horizons, in layers adjacent to limestone and in all horizons of a gibbsitic soil containing quartz.