Solution Chemistry Effects On Soil Hydraulic Properties: Changes with Changing Soil Water Content.

Elevated soil salinity has long been problematic in agriculture causing reductions in soil quality and crop yields.  This study re-examines how soil hydraulic properties are affected by solution chemistry and addresses uncertainties in our understanding of its impact on soils.  Here we explore the effects of changing irrigation water electrical conductivity (EC) on soil hydraulic conductivity, K, and soil moisture retention, θ, over a range of soil water tensions.  The results show that a decrease in EC from 20 to 0.25 dS m^-1, with the sodium adsorption ratio held constant at low to moderate levels, causes dramatic changes in K(θ) only after dropping below 1.5 dS m^-1 which is consistent with previous studies.  In addition and of particular interest is the magnitude of change in K with changing EC and decreasing θ.  Unlike current models that assume the decline in K due to solution chemistry is constant over the entire K(θ) range and equal to the change at K_sat, this study observes an exponential increase in the solution chemistry’s effect on K with decreasing θ.  These findings suggest that current models that ignore solution chemistry, or models that assume a constant K reduction for the entire K(θ) function, are over-estimating drainage.  Development of a more dynamic solution chemistry model that includes the solution chemistry effects presented here may improve irrigation, river, and groundwater quality and improve crop yields in systems struggling with salinity and water quality issues.