The stability of soils used for cropping in northern Victoria and southern New South Wales

Three hundred and six soil samples were classified for sodicity on the basis of exchangeable sodium percentage (ESP), and for spontaneous or mechanical dispersion on the basis of a dispersion test (Emerson 1991). Each sample was analysed for pH, electrical conductivity (EC), concentrations of exchangeable and soluble cations (Ca²⁺, Mg²⁺, Na⁺, K⁺), and concentration of organic carbon (OC). These variables were used to explain the sodicity and dispersive classifications of the 306 samples. Concentrations of exchangeable and soluble Ca²⁺, Mg²⁺, and Na⁺ along with EC and total cation concentration (TCC) significantly affected the sodicity and dispersion classification of the soil. A sodic soil was expected to disperse spontaneously, a non-sodic soil was not expected to disperse spontaneously. From this hypothesis the expected and observed dispersion class was compared with sodicity class. The expected result corresponded to the observed result 77% of the time and the hypothesis was accepted (P < 0.001).