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Methods for rapid and accurate soil tests are needed for the index properties of material attributes commonly applied in civil engineering. We tested the application of mid-infrared (MIR) spectroscopy for the rapid characterization of selected key stability-related soil properties. Two sample sets, representing different soils from across Lake Victoria basin in 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 ground (<0.5mm) soil was scanned using a high-throughput screening accessory for diffuse reflectance attached to a Fourier transform infrared spectrometer. The soil properties were calibrated to smoothed first derivative MIR spectra using partial least-square regression (PLS), and screening tests were developed for various limitation classes applicable in civil works using the soft independent modeling of class analogy (SIMCA). The hold-out full cross-validation coefficient of determination (r2)≥0.8 was obtained for the liquid limit (LL), linear shrinkage (LS), coefficient of linear extensibility (COLE), air-dried moisture content, (W) and cation exchange capacity (CEC). Further independent validation gave r2≥0.73 and the ratio of prediction deviation (RPD) 4.4–2.1 for LL, LS, COLE, W, CEC, plastic limit (PL), plasticity index (PI), and volumetric shrinkage (VS). The independent validation likelihood ratios for the diagnostic screening tests were: LL>55%, 4.2; PI>30%, 2.7; LS>12%, 2.4; exchangeable sodium (eNa)>2cmol (+) kg−1, 2.3; exchangeable sodium percent (ESP)>10%, 1.8; W>8.3%, 1.6, and Activity number (A)>1.25units, 1.5. MIR can provide the rapid assessment of several soil properties that yield stability indices in material testing for engineering land use. Further studies should test the ability of MIR PLS for establishing broader calibrations across more diverse soil types and the direct correlation of MIR to material functional attributes.

ABSTRACTMethods 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.

In March 2013, 40 leading experts from across the world gathered at a workshop, hosted by the European Commission, Directorate General Joint Research Centre, Italy, to discuss the multiple benefits of soil carbon as part of a Rapid Assessment Process (RAP) project commissioned by Scientific Committee on Problems of the Environment (SCOPE). This collaboration led to the publication of the SCOPE Series Volume 71 “Soil Carbon: Science, Management and Policy for Multiple Benefits”; which brings together the essential scientific evidence and policy opportunities regarding the global importance of soil carbon. This short communication summarises the key messages of the assessment including research and policy implications.