Carbonate weakens the interactions between potassium and calcareous soil

The ion interfacial transport driven by ion-surface interactions in calcareous soil has a profound impact on the nutrient storage and environmental buffer capacity of the main agricultural soils in dry and semi-arid areas. The roles that carbonate plays in preserving the soil's inorganic carbon pool and soil structure stability have been widely investigated, but its significance in the aforementioned microscopic processes, especially the influence of carbonate on the interfacial reaction kinetics of nutrient elements, is yet to be determined. In this study, potassium (K) was used as an indicator ion to investigate its affinity in carbonate-removed (CREM) and carbonate-reserved (CRES) calcareous soil using the general theory of ion diffusion in an external electric field. We discovered that (1) at a given initial K concentration, the carbonate in CRES soil retards the adsorption rate and diminishes the adsorption amount of K in calcareous soil, reducing the interfacial transport properties of nutrient ions at the solid-liquid interface of calcareous soils compared with CREM soil; and (2) this weakening of the interfacial transport effect on nutrient K originates from the soil carbonate, which prefers to weaken the electrostatic interaction intensity between K and the calcareous soil surface. Furthermore, this is due to the carbonate shielding effect on the surface adsorption sites of other soil components and the competitive relationship between K⁺ and cations released by carbonate dissolution. The influence of carbonate on the nutrient ion transport at the solid-liquid interface of calcareous soil has been investigated by soil electrochemistry theory-based ion adsorption kinetics, and the links between kinetic features and ion-surface binding energy have been clarified.