Chemical speciation of soil solution to assess calcium and aluminum uptake by coffe roots

Abstract

A greenhouse experiment was conducted with two acid soils to study Ca and Al uptake by coffee roots using the following salts: CaCO₃, CaCl₂, Ca(NO₃)₂, CaSO₄, and MgCO₃. Saturation extracts of the soil samples were analyzed for all major cations and anions to have input data for chemically speciating Al and Ca in the soil solution phase using a computer program GEOCHEM. All Casalts increased the concentration of total Ca_t in solution. CaCO₃ increased the concentration of Ca²⁺ and neutralized Al³⁺. CaCl₂ and Ca(NO₃)₂ increased the concentration of Al³⁺ and decreased Ca²⁺ in relation to CaCO₃. No significant ionic complexation of Cl^- and NO₃^- with Al was computed, but some with Ca as CaCl⁺ and CaNO₃⁺. Gypsum resulted in SO₄^2- ion-pairing with Al and Ca to form AlSO₄⁺, and CaSO₄^o, thereby decreasing Al³⁺ and Ca²⁺ in soil solution. Coffee dry matter increased with increasing Ca²⁺ and decreasing Al³⁺ in soil solution. The Ca uptake by roots decreased by lowering the valence of Ca in soil solution through complex formations: Ca²⁺ > CaNO₃⁺≥ CaCl⁺ > CaSO₄^o.