CATENARY RELATIONSHIPS OF DOWNLAND SOILS DERIVED FROM LOESS, SOUTH CANTERBURY, NEW-ZEALAND

Very limited information is available on soil variability within the large soil map units of the loess-mantled downlands of the east coast of South Island, New Zealand. In this study eight profiles were sampled in a catenary transect across a valley to assess the morphological, chemical and particle-size changes both within and between soil profiles for both sunny and shady aspects. Profiles from each landform element had similar sequences of horizons but thickness of horizons varied. Profiles on shoulder slopes had thinnest topsoil and subsoil horizons above underlying fragipans. There was a rapid thickening of topsoils and depth to fragipans immediately below the point of slope inflection between planar midslopes and concave lower slopes. The most striking difference in soil morphology was the overthickened topsoil horizons in footslope sites. This was attributed to effects of cultivation, either directly, through mechanical movement of soil material during cultivation operations, or indirectly, through the promotion of soil erosion. There was no indication of the expected catenary relationship involving translocation of exchangeable bases from upper to lower slopes. Differences in P-retention, KCl-extractable aluminium and clay content were identified in soils with different aspects but were not attributed to climatic differences.