Coefficients for estimating SAR from soil pH and EC data and calculating pH from SAR and EC values in salinity models

Robbins, Charles W. (1993) Coefficients for estimating SAR from soil pH and EC data and calculating pH from SAR and EC values in salinity models. Arid Soil Research and Rehabilitation. 7:29-38.

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Abstract

Data from highly weathered, low pH, sodic Australian soils have been
used to develop a method for estimating soil exchangeable sodium percentage (ESP)
or soil extract sodium adsorption ratio (SAR) from soil pH and electrical conductivity
(EC) data. The method can also be used to calculate soil pH in soil salinity models
using SAR and EC values. The pH was calculated as pH - A + (B x SAR^1/2)/(1 +
C x EC). Rewriting the equations in terms of SAR (or ESP), gives SAR (or ESP) -
[(pH - A)(1 + C x EC)/B]2 . This study was conducted to determine whether these
same methods could be used to predict the pH and SAR values for arid climate soils
that are only slightly weathered and are often sodic under natural conditions. Existing
pH, EC, and SAR data from Declo loam (coarse-loamy, mixed, mesic, Xerollic Calciorthids),
Freedom silt loam (fine-silty, mixed, mesic, Xerollic Calciorthids), and Mazuma
sandy loam (coarse-loamy, mixed (calcareous), mesic Typic Torriorthents) were
used to calculate the A, B, and C coefficients for the three high sodium soils. Coefficients
obtained for a particular soil site were then used to predict pH or SAR of soil
samples at additional sites and the correlation between calculated and measured values
were determined. The A values for the Idaho soils are about 0.8 greater than those for
the Australian soils, which were not completely base saturated. The Australian soils B
values were about twice that of the calcareous Idaho soils, and the C values were not
significantly different for the Australian and Idaho soils. In both cases the A coefficient
values were slightly smaller than or nearly equal to the smallest pH values in a particular
data set. Using coefficients from one location of a particular sodic or saline-sodic
soil to predict pH or SAR of the same soil, at a second location, was shown to be
practical. Each soil type, however, requires its own set of coefficients. These relationships
provide a rapid field method for estimating SAR or ESP from easily obtainable
EC and pH data once the A, B, and C coefficients are determined for a particular soil.
They also provide a method for pH calculation in soil salinity models that take into
account soil EC and sodium effects on pH.

Item Type:	Article
NWISRL Publication Number:	0792
Subjects:	Soil > Chemistry Research methodology Mass Import - autoclassified (may be erroneous)
Depositing User:	Dan Stieneke
Date Deposited:	20 Nov 2010 21:53
Last Modified:	01 Dec 2016 21:46
Item ID:	593
URI:	https://eprints.nwisrl.ars.usda.gov/id/eprint/593