Improving Estimates of Soil Salinity From Saturated Paste Extracts and Electromagnetic Induction Sensing.

Approximately one third of the soils in the US are affected by some degree of salinity. Most of these soils are found in the arid and semi-arid west where there is insufficient rainfall to leach salts out of the soil profile. Soil salinity is detrimental to the soil health, crop growth and quality. A standard parameter for quantifying salinity is the electrical conductivity of the saturated paste extract (ECe). A drawback of this method is the formation of ion pairs in the high ionic strength saturated paste extracts, which effectively decrease the measured ECe leading to the underestimation of soil salinity. We hypothesize that the saturation paste extract can be diluted to a point where ion pair formation is minimized; so that the ECe can be use to accurately predict soil salinity. Our conceptual model suggests a dilution factor of 1:1000 is appropriate to minimize ion pair formation in saline salt extract to values smaller than 0.04 dS m^-1. This concept was applied to the saturated paste extracts of 451 soils from Cache Valley, Utah. The anions, cations, and pH of the extract solutions where determined before and after dilution to determine the extent of ion pairing. The results were compared with predictions made using the Visual Minteq speciation model.