The CaCO3-CO2-H2O system in soils

Robbins, C.W. (1985) The CaCO3-CO2-H2O system in soils. Journal of Agronomic Education. 14(1):3-7.

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Abstract

Equations used to develop the CO2-Ca-pH relationships
in calcareous soils are reviewed. The equation

PCO2(Ca) = (H)2 Kc,

is used to draw a three-dimensional surface and to derive
three partial differential equations to illustrate the relationships
between CO2 partial pressure, Ca activity and
pH. Kc is a combination of Henry's Law constant, the
first and second dissociation constants for carbonic acid
and the calcite solubility product. The three dimensional
CO2-Ca-pH surface illustrates how the three parameters
relate to each other under ideal conditions. The partial
differential equations are presented to illustrate how
changes in one parameter affect the other two. The
CO2-Ca-pH surface provides a graphical method for introducing
the idea of three component equilibria, while
the partial differential equations provide a mathematical
representation of these interactions for those with chemical
thermodynamics or strong mathematic or modeling
backgrounds. Deviations from this ideal model in
natural systems are discussed for those who wish to extend
the discussion to natural systems.

Item Type:	Article
NWISRL Publication Number:	0548
Subjects:	Mass Import - unclassified
Depositing User:	Dan Stieneke
Date Deposited:	20 Nov 2010 21:52
Last Modified:	13 Jan 2017 21:53
Item ID:	436
URI:	https://eprints.nwisrl.ars.usda.gov/id/eprint/436