Influence of soil structure on the shrinkage behaviour of a soil irrigated with saline - sodic water

Abstract

Soil structural properties of swelling/shrinking soils play an important role in assessing hydraulic properties. However, the effect of shrinkage/swelling processes on structure formation and strength especially in saline–sodic soils, such as a Typic Chromexert, has not yet been clarified. In this study, we investigate the changes in the shrinkage pattern after applying saline sewage water and use a 3-parameter sigmoidal curve model to fit its shrinkage data. Our aims were to determine the overall effect of sewage water application on soil structure and shrinkage processes after applying saline–sodic water and to evaluate soil shrinkage behaviour through parameters in relation to soil properties. Three plots within the FILTER Project, which were irrigated for summer and winter irrigated cropping with around 1000 m3/ha every 2 weeks with different saline sewage effluent concentrations for >5 years, were sampled from the top horizon to 1.00 m depth. The exchangeable sodium percentage is greatly decreased due to the application of low salt concentration except in the deep horizon. Soil structural properties such as aggregate strength and hydraulic properties are improved, especially in topsoil horizon. The stabilised soil structure reduces the volume change of structural shrinkage. Three parameters of the shrinkage model, defined as α, m, and n, present different physical meanings in relation to soil structure. Parameters α and m have similar functions, both a significantly exponential relationship with aggregate strength and a linear relationship with structural and residual shrinkages, whereas parameter n has a significantly linear relationship with aggregate strength and with the slope of the proportional shrinkage. The relation between parameters of the model and shrinkage behaviour facilitates the prediction of changes in pore water and soil structure and will be a useful tool for modelling water flow in non-rigid soils.