Estimation of stability-related soil properties using mid-infrared spectroscopy for non-agricultural land use in Lake Victoria basin, Kenya

ABSTRACT Methods for rapid and accurate soil tests are needed for stability-related soil properties, which are valuable for non-agricultural land use. The study tested the applicability of mid-infrared (MIR) spectroscopy for rapid estimation of selected stability-related soil properties. Two sample sets, representing different soils from across the Lake Victoria basin of Kenya, were used for the study. A model calibration set (n = 135) was obtained following a conditioned Latin hypercube sampling, and a validation set (n = 120) was obtained from independent sites using a spatially stratified random sampling strategy. Air-dried and ground (<0.5 mm) soils were scanned using a high-throughput screening accessory for diffuse reflectance attached to a Fourier transform infrared spectrometer. Soil properties for interval-depth datasets were calibrated to smoothed first derivative MIR spectra using partial least-square regression (PLS) and the results were evaluated using hold-out full cross-validation. MIR spectra resulted in good prediction models with coefficient of determination (R2 ) ≥ 0.60 for air-dried moisture content (mc), liquid limit (LL), plastic limit (PL), plasticity index (PI), linear shrinkage (LS), coefficient of linear extensibility (COLE), volumetric shrinkage (VS), cation exchange capacity (CEC) and total sand content (tSa). Further independent validation gave R2 ≥ 0.72 and a ratio of prediction deviation (RPD) 3.8–2.0 for mc, LL, PI, LS, COLE, VS and CEC. MIR provides rapid estimation of several soil properties that provide stability indices valuable for non-agricultural land use in the Lake Victoria basin of Kenya. Further studies should test MIR PLS for interval/separate-depth calibrations and MIR screening of soil properties based on limitation classes commonly applied in civil works.