Browsing by Subject "Soil mapping"

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Development of MidDRIFTS methodologies to support mapping of physico-chemical soil properties at the regional scale
(2014) Mirzaeitalarposhti, Reza; Müller, Torsten
Changing climate conditions and land-use change severely affect key ecosystem processes in soils. Hence, regular monitoring of essential soil properties are required to implement appropriate soil management in agro-ecosystems. However characterizing soil properties at different spatial scales remains challenging, requiring a large amount of geo-referenced data by intensive sampling. Mid-infrared diffuse reflectance infrared Fourier transform spectroscopy (midDRIFTS) in combination with partial least square regression (PLSR) was applied as a rapid-throughput method to quantify soil properties and to assess soil spatial patterns at the regional scale in two agro-ecological areas. A pre-sampling at the regional scale was done to develop the most efficient midDRIFTS-PLSR prediction models by testing two different calibration procedures, i.e. cross-validation and independent validation, to quantify essential soil properties with 126 sample points. A generic MidDRIFTS-PLSR prediction model was developed to predict most soil properties of “unknown” samples accurately using independent validation approach. The next step was the integration of midDRIFTS-PLSR with geostatistics to facilitate regional soil property mapping. Developed midDRIFTS-PLSR models were used to predict TC, TIC, TOC and soil texture contents (clay, silt and sand) of the 1170 soil samples. The midDRIFTS-PLSR models accurately predicted all soil properties. Furthermore, the integration of midDRIFTS-PLSR-based predicted data with geostatisitcs resulted in high resolution maps of soil carbon and texture at the regional scale which are an improvement over the existing maps. As a further development of midDRIFTS approaches for soil quality assessment, spectral-based indexes for characterizing SOM quality and quantifying carbonate at regional scale were explored. MidDRIFTS peak areas corresponding to SOM functional groups (2930, 1620, 1520 and 1159 cm-1) were assessed to study the composition of SOM. The peak assigned for aliphatic C-H bond (2930 cm-1) was an appropriate index to investigate SOM fractions if the interference of carbonates was taken into consideration. Regression performance obtained between the peak at 2930 cm-1 and SOM fractions (e.g., R2 = 0.31 for Cmic) increased to R2 = 0.65 when high carbonate containing samples (total inorganic carbon > 1%) were excluded. The most accurate spectral index for carbonate was the peak area at 713 cm-1 when relating to TIC obtained by Scheiblers method (R2 = 0.98). In conclusion, it was demonstrated that midDRIFTS-PLSR is a rapid-throughput method for providing high-quality predictions of soil properties to update regional digital soil property mapping by integration with geostatistics. It opens a new possibility to gain high resolution data coverage of soil C and N pools, which is relevant for the application of SOM simulation models on a regional scale. However, to up-scale the approach for extended geographical areas, further efforts are needed to establish a national level spectral library by considering standardization of sampling, analytical reference analyses and midDRIFT spectroscopy techniques.