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 Ca (2+) and Cl- different pH values ranging from 3 to 7. The cation exchange capacity (CEC,) increased with soil organic carbon and pH and varied from 0 to 35 cmol(c) kg(-1) soil. The anion exchange capacity (AEC) reached 4.25 cmol(c) kg(-1) soil in Bo horizons at pH 4. The magnitude of the CECT and AEC variations was modelled according to CECT = 10(a1pH) * 10(B1) and AEC = - 10(a2pH) * 10(B2). Parameters a(1) and a(2) 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 a(1) and a(2) could be also useful to regroup soil types according to the nature of the properties that can be manipulated for their management. (C) 2001 Elsevier Science B.V. All rights reserved