Variation in soil physical properties between and within morphologically defined series taxonomic units

Abstract

Eyre, Templeton and Wakanui series are morphologically defined taxonomic units which are used to partition alluvial soil variation across the Canterbury Plains near Lincoln College in New Zealand. The wider significance of the classification criteria is here assessed by quantifying the variability of physical properties of hydraulic significance ['field-saturated' hydraulic conductivity (Kfs), moisture content and bulk density] between and within the three taxonomic units. The overall effectiveness of the morphologically based classification system in partitioning variation in soil physical properties is considered by using analysis of variance. The classification of soils according to texture and mottling criteria is generally effective in separating soils in terms of the selected soil physical properties. Although some topsoil physical properties do not differ significantly between pairs of taxonomic units, all subsoil properties are clearly distinguishable between Templeton and Wakanui series. The differences are mainly attributable to spatial changes in soil texture and pore characteristics. Different amounts of variation in physical properties, however, are still present within each taxonomic unit. The variation in physical properties amongst the combined series taxonomic units is reduced to differing extents by the classification. More than half of the variance in moisture content at both topsoil and subsoil depths amongst Templeton and Wakanui taxonomic units, for instance, is accounted for by the classification, and is thus due to differences between the two series. Little contribution is made by the classification in reducing the heterogeneity of Kfs in topsoils. The classification is particularly effective in separating Wakanui from Templeton taxonomic units in terms of subsoil Kfs, an important property controlling water movement and storage.