Intrinsic Relation between Soil Water Retention and Cation Exchange Capacity

Abstract

The authors hypothesize that soil water retention (SWR) is dominated by cation hydration in soils possessing a cation exchange capacity (CEC) at high suction range. This hypothesis leads to the identification of a unitary maximum gravimetric water content wmc, up to which all water molecules should surround the exchangeable cations. The unitary wmc can be obtained by using the CEC and hydration number of cations in soils. For a soil with an unknown CEC, the authors reveal that wmc can be found independently from either the SWR based on the hysteretic behavior of a soil’s specific moisture capacity (SMC), or from the SWR curve interpreted by a Brunauer-Emmett-Teller (BET) sorption model. The authors demonstrate experimentally that wmc computed independently from the previous approaches accord well with the calculated wmc, indicating the validity of the hypothesized unitary state and applicability of the SWR-based methodology in determining the CEC of soils.