Empirical equations for prediction of major cation concentrations in soil solution using concentrations in water extracts

Figures & data

Table 1 Range of selected chemical and mineralogical properties of the soil samples used

Properties	Range of values or descriptions
	Non-Andisols	Andisols
Organic carbon (g kg^−1)	9–62	22–71
pH (in water)	5.22–7.68	5.62–7.33
Clay mineralogy	Either kaolinitic, smectitic or mixed illitic–vermiculitic–kaolinitic	Allophanic
Allophane content (g kg^−1)	–	150–300
Water content at soil solution separation (kg kg^−1)	0.240–0.500	0.447–0.876
Water content at water extraction (kg kg^−1)	4.99–7.66	5.00–5.79

Figure 1  Ion concentrations predicted using multiplication by the dilution ratio plotted against the measured concentrations in soil solution. (○) non-Andisols; (•) Andisols.

Figure 2  Total amount of cations in water extract plotted against the total amount of cations in soil solution for (a) all soils and (b) soils in which the soil solution was unsaturated with respect to gypsum. (○) non-Andisols; (•) Andisols.

Figure 3  Ion concentrations predicted using multiplication by the dilution ratio plotted against the measured concentrations in soil solution for soils in which the soil solution was unsaturated with respect to gypsum. (○) non-Andisols; (•) Andisols.

Table 2 Regression equations relating ionic concentration in water extract with the concentration in soil solution

Cation	Equation
Ca	[Ca]ss = 0.8553 r d[Ca]wex − 0.9282	(r^2 = 0.9651***)
Mg	[Mg]ss = 0.9346 r d[Mg]wex − 0.6645	(r^2 = 0.9766***)
K	[K]ss = 0.4978 r d[K]wex − 0.8984	(r^2 = 0.9215***)
Na	[Na]ss = 0.7092 r d[Na]wex − 0.5283	(r^2 = 0.9322***)
***. r d, dilution ratio (i.e. the ratio of the water content at water extraction to that at soil solution separation); [], concentration in mmol L^−1; ss, soil solution; wex, water extract.

Figure 4  Ion concentrations predicted by the regression equations plotted against the measured concentrations.