Csillag, J., T. Tóth, and M. Rédly. 1995. Relationships between soil 
solution composition and soil water content of Hungarian 
salt-affected soils. Arid Soil Research and Rehabilitation. 9:245-260.

Soil solution fractions retained in the soil with suctions 
not reaching -1500 kPa were centrifuged from three salt-affected 
soils. Hyperbolic relationships were set up in a wide soil water 
content range (from -250 kPa water potential to 1:10 soil:water 
ratio) between water content and electrical conductivity as well 
as concentrations of the dominant ions present in the liquid phase. 
It was shown that the parameters of the equations reflected on the 
salt content and composition of the soils, as well as on the change 
of the solubilities of the salts and ion-exchange processes with 
soil water content. 

Ion-pair concentrations and "free" ion activities were computed 
by taking into account the electrostatic interactions of ions 
in the solution. Na+/divalent cation ratio (SAR) was expressed 
from cation concentrations and activities. It was shown that 
depending on salt content and composition, as well as on water 
content of the soil 1.: the ratio of ion activities to 
concentrations was very variable (in some cases, at field 
capacity, in concentrated solutions, divalent ions' activities 
were even 6 times lower than concentrations); 2.: SAR was 
always (at field capacity, for example, nearly 2 times) higher 
if it was calculated from activities, and increased more with 
decreasing soil water content than SAR obtained from measured 
cation concentrations.