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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.

ABSTRACTA field study was carried out for 2 seasons (November to February 1999 and April to August 2000) to investigate the influence of irrigation on maize growth, nitrogen uptake and yield. The experimental design was randomized complete block design laid out as split plot with water regime as main plots (irrigated, rainfed), and factorial combinations of N (0, 50, 100 kg N/ha) and P (0, 25 kg P2O5) as subplots. Data collected included leaf area index (LAI), photosynthetically active radiation (PAR) interception, total dry matter (TDM), nitrogen uptake and maize grain yield. Phosphorus had no effect on growth and yield, so the data were pooled for P. In the wet (350 mm rainfall) Short Rains, 1999 (SR99), irrigation had no effect on LAI and fractional PAR interception but significantly increased total N uptake, TDM and grain yield by 50 to 100%. Under low rainfall (143 mm) in the Long Rains 2000 (LR00), irrigation increased LAI and PAR interception by 50 to 100% and N-uptake, TDM and grain yield by 10, 10 and 34 fold respectively. However there was no significant response to N fertiliser application without supplemental irrigation. Nitrogen application above 50 kg/ha did not improve maize growth and yield in both seasons. Supplementary irrigation can therefore increase maize yield even at low fertiliser input level in semi-arid Kenya.