Measuring and estimating the hydrological properties of a soil crust

Formation of soil crusts results in reduced infiltration, increased runoff, and reduced rainfall and irrigation efficiency. Improved knowledge of the hydrological properties of soil crusts is required to improve simulation of infiltration and soil water movement in crop-soil-water models. Development of soil crust algorithms in soil water models is limited by a lack of in situ and laboratory approaches for measuring the physical properties of soil crusts. In this study we evaluate a number of novel and modified approaches for determining changes in the hydraulic properties of soil crusts formed in an intensively cropped sandy loam. Physical crust formation over a 71 day period resulted in an increase in surface soil density from 1.17 to 1.51 g cm^-3, a reduction in infiltration from 474 to 33.2 mm h^-1, and a decrease in unsaturated hydraulic conductivity at -0.05 kPa from 136.9 to 10.14 mm h^-1. Whilst the ability to determine the van Genuchten properties of soil crusts was progressed, uncertainty with matching crust thickness to sampling depth, and difficulty measuring the total porosity of soil crusts resulted in error and uncertainty in the estimation of the θs parameter and to a lesser extent the α and ɳ parameters. Further work is required to improve the development of simple, in situ means of measuring or estimating the physical properties of soil crusts.