Quantifying variability of soil physical properties within soil series to address modern land-use issues on the Canterbury Plains, New Zealand

Abstract

Lack of accurate data to estimate soil physical properties for soil types is limiting the wide application of simulation models to address modern environmental and land-use issues. In this study, systematic sampling of soil profiles for soil physical characteristics has provided an improved basis upon which to estimate a number of soil physical properties for 4 soil series. The selected soils form a soil drainage sequence on the post-glacial surface of the Canterbury Plains and vary from shallow sandy loam, well-drained soils to deep clay loam, poorly drained soils. Three profiles within 3 map units were sampled for each of 4 soil series. Three horizons in each soil profile were sampled for soil porosity values, particle size, and saturated and near-saturated hydraulic conductivity.

Variability in all data, as shown by coefficient of variation, increased in the order: total porosity = field capacity < wilting point < total available water = clay content < readily available water < macroporosity < sand content < hydraulic conductivity. Hydraulic conductivity exhibited high variability within horizons, between profiles, and within soil series. Temuka subsoils had extremely high variability in saturated hydraulic conductivity and this could be explained by their coarse prismatic structure.

Analysis of variance identified horizons that differed in soil physical properties between soil series. Horizons that do not differ between series may be given pooled soil property values for the pooled series. Total porosity, field capacity, wilting point, clay content, and near-saturated hydraulic conductivity had the greatest number of differences (60–70%) between series comparisons, while total available water had fewest differences (5%). The series with greatest differences in drainage class (Temuka compared with Eyre or Templeton soils) recorded the largest number of differences in water release characteristics and particle size. There were few differences between well-drained Eyre and moderately well-drained Templeton series. Subsoils of Eyre series differed in hydraulic conductivity from subsoils for the other 3 series, but few differences in hydraulic conductivity were found between horizons of Templeton, Wakanui, and Temuka series. Hydraulic conductivity estimates for these series can therefore be pooled.