Mineralogical, chemical and charge properties of Geric Ferralsols from New Caledonia

The mineralogical, chemical and surface charge properties of Geric Ferralsols of New Caledonia were examined. These soils, which corresponded to two soil mantles formed either on ultramafic rocks or volcanic ejecta and ashes, were respectively dominated by iron and aluminium oxides. The electric charge characteristics were studied by measuring retention of Ca2+ and Cl− at different pH values ranging from 3 to 7. The cation exchange capacity (CECT) increased with soil organic carbon and pH and varied from 0 to 35 cmolc kg−1 soil. The anion exchange capacity (AEC) reached 4.25 cmolc kg−1 soil in Bo horizons at pH 4. The magnitude of the CECT and AEC variations was modelled according to CECT=10a1pH∗10B1 and AEC=−10a2pH∗10B2. Parameters a1 and a2 were low for samples with high organic carbon (from 0.10 to 0.19 and from −0.44 to −0.66, respectively) and could increase to 1.25 and −0.39, respectively, when organic carbon content decreased. The parameters a1 and a2 could be also useful to regroup soil types according to the nature of the properties that can be manipulated for their management.