Pj. Van Erp et al., Actual cation exchange capacity of agricultural soils and its relationshipwith pH and content of organic carbon and clay, COMM SOIL S, 32(1-2), 2001, pp. 19-31
For the set up of a multinutrient 0.01 M calcium chloride (CaCl2) soil test
ing program a conversion from conventional soil testing programs to a CaCl2
program has been proposed in literature. Such conversion should be based o
n the relationship between test values of the conventional method and the C
aCl2 method. For magnesium (Mg) it was shown in earlier work that the conve
rsion could be improved when the actual cation exchange capacity (CEC) of t
he soil, CECact, was taken into account. However, determination of CECact n
ecessitates an extra analytical procedure. The goal of this study was to te
st a procedure for estimating CECact of a soil. In this procedure, CECact w
as calculated as the summation of the estimated charge of organic carbon (C
) and clay in the soil at pH(act). the actual pH of the soil. A series of 3
9 test soils representing agricultural soils in The Netherlands was used to
derive the pH dependency of the negative charge of organic C and clay. The
following relationship was found: CECact: [M(1)X0.0624] + [M(2)X(0.295-D(2
)(pHact))]. In this relationship, M(1) and M(2) represent clay and organic
C in g kg(-1) dry soil, respectively, and D(2)(pHact) the difference in neg
ative charge of organic C at pH(act) and pH 8.1. The pH(act) equals pH meas
ured in 0.01 M CaCl2. The relationship was tested on another dataset of 38
agricultural soils. There was good agreement between the calculated and mea
sured CECact (R-2=0.89). It was concluded that the procedure can be used fo
r estimation of CECact..