Genesis and classification of a sequence of soils formed From aeolian parent materials in East Otago, New Zealand

Abstract

Eight soil types occurring between 60 and 480 m altitude on Waiora Research Farm, East Otago, New Zealand, are described. The soils are classified in the New Zealand Genetic and Soil Taxonomy classification systems respectively as yellow-grey earths (Fragiochrepts and Fra'giaquepts), yellow-brown earths and podzolized yellow-brown earths (Dystrochrepts), and a podzol (Placorthod). The soils form a development sequence related primarily to altitude, demonstrated chemically by greater leaching of the higher altitude soils and morphologically by the presence of a fragipan in the drier soils at lower altitude and an iron pan in the soils at higher altitude. Fragipans of yellow-grey earths at higher altitudes are modified by the effect of perched water. In the yellow-brown earths, podzolized yellow-brown earths and podzols firm subsoils with gammate colour patterns are found in some profiles and are regarded as relict features of fragipans formed under a previously drier climate. Planar fractures in lower B and upper C horizons, subparallel to the present soil surface, are attributed to breaks of loess deposition due to intermittent colder conditions. Relationships between soils are better demonstrated by the New Zealand Genetic Classification, because of lack of differentiae related to leaching or phosphorus sorption properties at subgroup or family level in the USDA classification.