Calculating pH from EC and SAR values in salinity models and SAR from soil and bore water pH and EC data

Robbins, C.W. and Meyer, W.S. (1990) Calculating pH from EC and SAR values in salinity models and SAR from soil and bore water pH and EC data. Australian Journal of Soil Research. 28(6):1001-1011.

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Abstract

Currently used soil salinity models do not contain a mechanism for including exchangeable
sodium effects on soil pH. A method is needed that allows pH calculation from the
sodium adsorption ratio (SAR) or exchangeable sodium percentage (ESP) and electrical
conductivity (EC) data. This study developed a simple method for calculating saturated
soil paste and aqueous solution pH from SAR (or ESP) and EC data and compared the
results with measured values from a number of soils and subsurface waters. The equation
pH - A+{B*(SAR)^1/2 /(1+C*EC)} estimated soil pH from EC and SAR or ESP values. When
rewritten as: SAR or ESP = {(pH-A)(1+C*EC)/B}^2 , the SAR or ESP was estimated from pH and
EC data. By using shallow bore (well) water and soil extract data from the Murray Basin,
values were determined for the scalar terms A, B and C. These values differed among
subsurface water and soil types, however, the range of each scalar was reasonably small.
It was found that a range of at least 2 - 5 pH units in the calibration data was necessary
to obtain reliable regression between predicted and measured pH and SAR or ESP values.
When these conditions were met, the predicted results were satisfactory. These relationships
provide a method for pH calculation in soil salinity models which takes into account soil
EC and sodium effects. They also provide a rapid field method to estimate SAR or ESP from
easily obtainable EC and pH data. Further research is needed to define the factors that
determine the values of A, B and C.

Item Type:	Article
NWISRL Publication Number:	0716
Subjects:	Soil > Chemistry Research methodology Mass Import - autoclassified (may be erroneous)
Depositing User:	Dan Stieneke
Date Deposited:	20 Nov 2010 21:53
Last Modified:	03 Jan 2017 17:13
Item ID:	539
URI:	https://eprints.nwisrl.ars.usda.gov/id/eprint/539