Formation and Properties of Clay-Polymer Complexes. Developments in Soil Science: 9. B.K.G. Theng. Elsevier,Amsterdam, 1979, 362 pp., U.S.$64.50, Dfl. 132.00

Weathering products of Vitrandept profiles on the Kaingaroa plateau, central North Island, New Zealand, were investigated by analysis of oxalate extracts and by chemical and mineralogical analysis of clays of selected soil horizons. Comparisons were made between profiles under a Pinus radiata (D. Don) stand and profiles under an adjacent area of manuka native scrub, Leptospermum scoparium (Myrtaceae).Clay fractions (< 2 μm) of A₁₁ horizon under pine had significantly higher SiO₂/Al₂O₃ mole-ratios (mean SiO₂/Al₂O₃ = 12.2) than A₁₁ horizon under manuka (mean SiO₂/Al₂O₃ = 7.1). No effect of vegetation on clay fractions of B horizon was evident, these clays having much lower SiO₂/Al₂O₃ mole-ratio (1.5). Oxalate-extractable Al, Fe and Si values of < 8-mm fractions of A, B and C horizons showed no differences attributable to present vegetative cover.SiO₂/Al₂O₃ mole-ratios of oxalate extracts increased with increasing depth, and paleosols at > 2 m depth under pine had significantly higher SiO₂/Al₂O₃ mole-ratios in oxalate extracts (mean SiO₂/Al₂O₃ = 2.0) than paleosols under manuka (mean SiO₂/Al₂O₃ = 1.6). That soil horizons at > 2 m depth are in the zone of resilication is indicated by: (1) the greater SiO₂/Al₂O₃ mole-ratios of oxalate extracts of paleosols than surface horizons; (2) lysimeter leachate composition; and (3) the presence of authigenic halloysite at > 2 m depth in soil profiles.