Rapid estimation of Brilliant Blue concentrations in soil by vis diffuse reflectance spectroscopy

Brilliant Blue is often used to trace water movement in soils. Its concentration in soil samples is usually determined by extraction — a laborious procedure with varying accuracy. In this feasibility study, we show that Brilliant Blue can be estimated directly by visible (vis) diffuse reflectance spectroscopy (DRS). We build a PLSR (partial least squares regression) model for the concentration range of 0.1 to 15 mg Brilliant Blue per g soil with an RMSE (root mean square error) of 1.35 mg g− 1 and an Radj2 of 0.88. However, as the method is based on visible spectra, prediction accuracy can be altered by variations in soil colour between calibration and prediction data sets. Therefore, we recommend a site specific calibration based on typical soil colours and an expected range of Brilliant Blue concentrations.