Rapid Method for Assessment of Soil Structural Stability by Turbidimeter

A rapid and inexpensive method to evaluate soil structural stability via assessment of soil clay dispersion is needed. Such a method would provide critical information for decision-making for soil and agricultural management not currently undertaken due to the expense of testing. The aim of this work was to validate the use of a turbidimeter for quantifying clay released from soil and to relate this back to dispersive parameters. Ten Australian soils with different physicochemical properties were studied. Six-step dilution was used to adjust the clay suspensions sequentially by dilution from a datum concentration of 4000 nephelometric turbidity units (NTU). The linearity of turbidity by dilution was verified, considering the effects of soil color and mean particle size. There was a strong correlation between turbidity (NTU) and dispersed clay (mg L-1, % of soil) for each soil. Clay particle size was related to turbidity response, although the coefficients between turbidity and dispersed clay were very close irrespective of mean particle size differences. Dispersed clay was concluded to be accurately quantified using a turbidimeter after spontaneous and mechanical dispersion. A semi-quantitative dispersion assessment chart was developed for rapid assessment of soil structural stability, the application of which is intended to provide rapid diagnosis and to act as an important index for soil management practitioners. Additionally, when dispersed clay was combined with electrical conductivity and clay content parameters, the dispersive indices (cation ratio of soil structural stability and exchangeable dispersive percentage) were reasonably predicted at a resolution useful for farm management decisions.