Variation in soil properties on two partially revegetated saline scalds in south-eastern Australia

Abstract

During 1999 and 2000, topsoil properties were sampled on a 3 by 3 m grid at 2 saline scalds on the inland slopes of New South Wales (NSW): Bocobra (0.11 ha) and Rugby (0.12 ha). Variability was examined in terms of range, standard deviation and coefficient of variation, maps with interpolated ‘contours’, and variograms. High variability was evident in all soil properties. pH1:5 water ranged from 4.8 to 8.0 at Bocobra and 5.9 to 9.0 at Rugby. Spatial ‘highs’ were evident at both sites but Rugby, which was mostly neutral, had both highs (alkalinity) and lows (acidity). Electrical conductivity (EC1:5 water) ranged from 0.5 to 6.6 dS/m at Bocobra and 0.1 to 2.6 dS/m at Rugby and was expressed spatially as highs across the sites. Concentrations of soluble ions were highly variable with both highs and lows evident. Concentrations of sodium and magnesium at Bocobra were highly correlated with EC1:5 water. Variability in EC and pH were high in comparison with published data from much larger areas of non-saline soils. An indication of temporal variability was obtained by carrying out an electromagnetic induction survey on 2 occasions. Despite changes in spatial patterns over time, EMh and EMv values were highly correlated at 1 site but not at the other. Variogram analysis suggested that changes in some variables, e.g. soluble potassium, changed markedly over distances less than 3 m. For most variables, the full range of variability occurred over distances of 8–10 m, though for some, e.g. soluble calcium, a distance of around 19 m was indicated. Variability cannot be ignored when planning revegetation projects or experiments. Partly because of their temporal variability, electromagnetic induction survey results (which were not calibrated with soil profile ECs in this study) may not provide useful guidelines for strategic soil sampling nor for locating experimental plots on scalded saline sites. Consideration should also be given to testing variables other than EC, e.g. pH and calcium, which may also limit plant growth on saline scalds.