Development of near infrared spectral library of Danish soils

This paper describes the methodology for the establishment of a Danish soil Near InfraRed Spectroscopy (NIRS) library. In order to make an efficient application of NIRS in the field for soil property mapping, it is necessary to establish a NIRS library for global calibration. Representative 3,534 samples from a 7 km grid sampling were chosen to cover variability in the geographical area of Denmark. Partial least square regression was used to build a regression model between SOC and the spectra. The data set was divided into three subsets: calibration, validation and prediction. Outliers were removed from spectral and reference data. The calibration result for non-organic soils was R 2 =0.81, RMSE=0.22, while validation was R 2 =0.81, RMSE=0.22 and RPD=2.3. This indicates good prediction abilities. The results were also tested on independent datasets, with the following results: R 2 =0.82, RMSEP=0.21 and RPD 2.4. Likewise, the calibration result for organic soils was R 2 =0.82, RMSE=13.70 while validation was R 2 =0.81, RMSE=13.5 with RPD=2.4. Prediction of the independent data set was also satisfactory with the R 2 =0.86, RMSEP=13.80 and RPD= 2.7.