Discrepancies between soil solute concentration estimates obtained by TDR and aqueous extracts

Abstract

Soil moisture (&thgr;) changes modify the electrical conductivity of the soil solution (EC_w) by varying the amount and composition of dissolved ions, their activity coefficients, and soil tortuosity. Theoretically expected, it was experimentally confirmed that the contribution of common reactions (precipitation–dissolution, adsorption–desorption, and complexation) to solute composition is not always a linear function of soil : water ratios. Using the driest or wettest q as references, correcting for dilution only when &thgr; changed, did not fully reconstruct the salinity. Bulk soil EC (EC_a)–EC_w linkage, based on the same mechanisms, is shown to have variable, curvilinear relations for soils of medium salinity levels, which are enhanced by the presence of sparingly soluble salts and clay content. An extreme disagreement between EC_w and EC_c (EC of 1 : 1 soil : water extracts adjusted for &thgr;) was found for a clay soil, where up to ~2 dS/m the slope was negative.