Spectral properties and hydraulic conductance of soil crusts formed by raindrop impact
In this study, a controlled spectral investigation of the properties of structural crust, using infiltration rate as an indicator, was carried out, on a grumusol (typic chromoxerets) soil. The scope of this paper is to investigate the spectral relationship between structural crust and the infiltration rate and some related properties of a grumusol soil. Structural crust is a thin compact layer generated on the soil's surface after rainstorm events due to raindrop energy. The crust, which is a result of physical segregation and rearrangement of soil particles, affects some of the soil's physical properties, such as infiltration, run-off and soil erosion. A set of soil samples was subjected in the laboratory to increased levels of cumulative energy from a simulated rainstorm, while measuring the infiltration rate. The result was a set of soil samples with increased levels of crusting and correspondingly reduced infiltration rates. After drying the soil samples, their spectral parameters across the SWIR region (1.2 m-2.4 m) were studied in the laboratory. Empirical relations were found between the infiltration rate and reflectance values (either in raw or in first derivative domains). A spectral ratio manipulation, using a fog type rain treatment (characterized as having no rain energy) as reference, confirmed that, within the spectrum, changes in both albedo and absorption enabled the crust to be detected using reflectance radiation. This is basically because fine (mostly clay) mineral enrichment processes occurred at the surface of the crusted soil. These minerals (montmorillonite, calcite) are spectrally active across the selected spectral region. Although further study is required to fully account for other soils, rainstorm energies and water qualities, this technique suggests great potential as a tool for rapid, non-destructive, in situ assessment of crusted soil properties.