9. Oxidic Soils

Oxidic Soils occupy less than 1% of New Zealand, occurring in small areas throughout Northland, but concentrated near Kerikeri. New Zealand’s Oxidic Soils represent a southern limit of the globally extensive Oxisols which occur mainly in the tropics and subtropics. Oxidic Soils form in New Zealand where conditions favour the most intense weathering. Thus Oxidic Soils occur mainly on readily weatherable, iron-rich, basaltic to andesitic volcanic or mafic/ultramafic igneous rocks and scoriaceous deposits on sites that have been stable, potentially for millions of years, in the warm, humid environment of Northland. The parent materials of Oxidic Soils have been almost totally transformed to clay minerals, oxides, and oxyhydroxides, including gibbsite, goethite, haematite, and ferrihydrite. The soils have a friable, fine polyhedral, structure although some may include horizons comprising over 50% iron- or aluminium-rich nodules giving a gravelly texture. The soils are highly leached and low in nutrients, but with good fertiliser management are used to successfully grow citrus and other subtropical crops. The first grape vines in New Zealand were probably planted on Oxidic Soils by an associate of Samuel Marsden at Kerikeri in 1817, and the first British-style farm was established on Oxidic Soils inland from Kerikeri in 1830.