A comparison of soil texture measurements using mid-infrared spectroscopy (MIRS) and laser diffraction analysis (LDA) in diverse soils

Abstract

Spectroscopic methods for the determination of soil texture are faster and cheaper than the standard methods, but how do the results compare? To address this question, laser diffraction analysis (LDA) and mid-infrared spectroscopy (MIRS) analysis have been compared to conventional sieve-pipette measurements of texture in diverse European and Kenyan soils. To our knowledge this comparison between LDA and MIRS has not been made previously. It has used soils with a broad range of organic carbon (OC) contents to investigate whether, as in other techniques, clay-OC aggregation affects the estimation of clay with MIRS. The MIRS predictions of clay content were much better than the LDA measurements, but both techniques gave good measurements of sand content. The MIRS over-estimated clay at low clay content and under-estimated at high clay content (calibration set R2 = 0.83). The LDA over-estimated clay by ~ 60% (calibration set R2 = 0.36), indicating that the widely used clay threshold of < 8 µm was too high, and < 4 µm was found to be more accurate. In samples with < 5% OC content, both the LDA and MIRS gave very good clay predictions (R2 = 0.88 and 0.81, respectively). But in predictions of clay content in samples with > 5% OC the LDA under-estimated (R2 = < 0.1) and MIRS over-estimated (R2 = 0.34) clay content. In soils with OC removed, the MIRS prediction of clay content improved, indicating interference between over-lapping spectral regions for organic and mineral constituents. Unlike granulometric measurements of texture such as the LDA, MIRS analysis is not subject to the limitations imposed by the shape and density of particles. It was concluded that in typical agricultural soils with < 5% OC and < 60% clay content, both techniques could be used for cheap, fast and reliable estimates of soil texture.

Estimating Soil Properties and Nutrients by Visible and Infrared Diffuse Reflectance Spectroscopy to Characterize Vineyards

“…As a key factor for site-specific management practices, Angelopoulou et al [24] recently reviewed laboratory and proximal sensing spectroscopy in the VIS, NIR, and SWIR wavelength regions for soil organic matter estimates. MIR spectroscopy and laser diffraction analysis (LDA) have also been demonstrated to be useful for calculating organic matter and clay content in soils [25].…”

Experiences of soil physical measurements with laser diffractometer and their application possibilities in soil water management research

“…The application of the general modified size limit of 7 µm resulted in different degrees of RMSE improvements for the three databases: the most spectacular improvement for the regional database (on which we verified this optimal value) and the least spectacular improvement for the continental database. One explanation for this can be found in a statement by Thomas et al (2021), who said that if a data set is dominated by sand textured soils, the limit is close to 2 µm and if, on the contrary, clay textured soils predominate, the optimal size limit is around 8 µm. In our case, the continental database contained the sandiest soils and the regional database the most clayey soils.…”

Assessing the Information Potential of MIR Spectral Signatures for Prediction of Multiple Soil Properties Based on Data from the AfSIS Phase I Project

“…The search for an effective model to estimate soil texture is a frequent topic in soil science research [ 44 ]. The estimates of the content of the different fractions vary in terms of RMSE values ( Table 1 ).…”