Soil variability within land systems and land units at Monarto, South Australia

Abstract

The utility of a 1:100,000 scale land system survey near Monarto was assessed by using the profile data obtained from remapping part of the area, at 1:25,000 scale, to soil series and types by the free survey method. (i) The Land Systems: On a test for the completeness of the soil profile classes, it was found that no classes had been missed in the land system survey: all soils mapped in the free soil survey had been previously described in the land system report. The success of the survey in estimating the proportion of profile classes was 78 %, and the score for purity, the chance that any profile class can be correctly predicted from the map and report, was 37%. From these tests the survey was judged a success. (ii) The Land Units: The land systems were mapped into their component land units, and their quality or utility was assessed by measuring the variation of soil properties within each unit. While there was a statistically significant reduction in variability within the land units compared with that for the whole area unmapped, the amount of reduction was slight. The variability of individual properties, as indicated by coefficients of variation, varied widely. Least variable were B horizon texture, thickness and structure, and A horizon texture. The quality of the Monarto land system map would have been improved by the use of medium-scale colour aerial photos and a different field inspection method. It is advocated that the concept of the land unit be dropped.