Some aspects of the cation status of soil moisture

Summary

The effect of potassium ions on a River Estate soil-water system was investigated by equilibrating the soil with 0.0001 to 0.02M KCl solutions. Soil solutions were obtained from soil samples prepared over a wide range of solution/soil ratios, both within and outside the field range. The soil-soil solution equilibrium remained undisturbed over the field range of solution/soil ratios, 0.25 to 1.0, for the 0.0001M 0.0002M, and 0.0005M KCl systems. Values of pK−1/2p(Ca+Mg) for these systems tended to decrease at ratios greater than 1.0 and with increasing strength of the KCl-equilibrating solutions. This is suggested to be due to the increasing potassium release from the soil with increasing solution/soil ratio for the 0.0001M KCl system and the increasing amounts of potassium present in the 0.0002M, 0.0005M, and 0.02M KCl systems.

Both release and uptake of potassium were shown to be functions of the potassium concentration of the equilibrium soil solution. A value K₀, was defined as the concentration of potassium in the soil solution when potassium was neither released nor taken up by the soil. It is suggested that if this value is known, measurement of the soil solution potassiujm concentration under any particular conditions would indicate whether potassium was being released or taken up by the soil.

It was deduced that the exchange complex of this soil had to be 62 per cent saturated with potassium before fixation occurred.