Estimating of the Soil Aggregate Size Fraction in Arid and Semi-Arid Soils using Reflectance Spectroscopy

ESTIMATING THE SOIL AGGREGATES SIZE FRACTIONS IN ARID AND SEMI-ARID ENVIRONMENTS USING PEDOTRNASFER FUNCTIONS AND SPECTRAL ANALYSIS

                                                 

This paper investigates the relationship of six aggregation fractions (2-1.4mm F1; 1.4-1.0 mm F2; 1.0-0.5 mm F3; 0.5-0.25 mm ; F4; 0.25-0.1mm ; F5, 0.1mm > F6) and their average (AVG) with relation to 74 soil attributes.  The database used in this study is based on the heritage soil spectral library (SSL) of Israel over both semi-arid and arid regions representing seven global soil orders from the  USDA list. The database is composed of chemical, physical and spectral measurements. The spectral data consisted of reflectance measurement using the IEEE  standard protocol and across the VIS-NIR-SWIR spectral region as well as XRF analyses of microelements and XRD determination, wet chemistry analysis and quantitative assessment of the soil mineralogy. The correlation matrix between all attributes enables to isolate four cementation agents (CAs) of the soil micro aggregation namely: clay content, clay mineral specious (smectite), organic matter, and free iron oxides contents. Generating a Pedo Transfer Function (PTF) using these CAs revealed equations that well predict the aggregate size fraction of F1,F2,F3, and the average aggregation stage (AVG ) of all soils. A separate spectral-based analysis to evaluate directly the fraction sizes from reflectance measurements without any prior information regarding the CAs, was also generated and revealed high statistic performance with spectral assignments that belonged to the four selected CAs and their derivatives. The final conclusion was that the micro aggregation stage of soil can be assessed directly or indirectly via PTF and also by using spectral analysis and data mining approaches. Assuming that the reflectance information from hyperspectral remote sensing means such as EMIT (NASA initiative) PRISMA (ASI) and EnMAP (DLR) are available today (2022) this approach may add a great deal to the NASA  mission aims at investigating the potential of soil to act as a dust source.