The data and findings discussed here come from the cited paper and do not represent test results from VISPEK equipment.
For the same soil, the spectra and prediction results may be different if the particle size is different. This study uses homologous soil and controlled nitrogen addition conditions to compare the effects of particle size, and isolates physical sample preparation factors that are easily overlooked in model development, demonstrating that stable measurements require simultaneous management of chemical composition and scattering conditions.
Summary
The study divided the homologous soil into multiple particle size groups, added urea and then dried and pressed into tablets, and compared the pretreatment and wave-selective PLS models. The moderate particle size group performs better, and mixing particles with larger differences will reduce the effect. The results come from artificial nitrogen-added tablets and cannot be used as the detection accuracy of total nitrogen in natural wet soil; there are still differences in the expression of concentration series and sample counts in the original text.
(AI-generated conceptual illustration for context; it is not data from the paper, a photograph of the research equipment, or a VISPEK product diagram.)
Why It Matters
Fixing the particle size and sample presentation reduces the chance of misinterpreting differences in scattering as changes in chemical content.
Methods and Reference Measurements
The soil from the same source was divided into 6 particle size groups, and nitrogen content change samples were prepared with urea solutions of different concentrations. After drying and tableting, there were 108 parts in each group, a total of 648 parts. Reflection spectra were collected using a 900–1700 nm point instrument, and 930–1670 nm were retained for modeling. Compare SG, detrending, SNV, first derivative and various PLS wave selection methods, and examine the impact of spectral mixing of different particle sizes on predictions.
Wavelengths and Acquisition Parameters
| Band/parameter | Original meaning and usage instructions |
|---|---|
| 900–1700 nm | Original instrument collection range |
| 930–1670 nm | Actual preprocessing and modeling interval |
| around 1394 nm | The particle size-related reflection difference that the paper focuses on comparing is not the exclusive spectral line of nitrogen. |
Key Findings
PLS predicted Rp²=0.983 and RPD=6.706 for the 0.18–0.28 mm particle size group. Particle sizes that are too large or too small will perform poorly, and mixing particle sizes with large differences will also reduce the model effect.
Limitations and Interpretation
The data comes from a single soil and artificially added nitrogen tablets, and cannot be directly used as the accuracy of total nitrogen detection in natural wet soil; the concentration series in the original text is inconsistent with the sample count.
Band and model boundaries: This example uses original measurements or independent verification branches that lie entirely within 250–1700 nm.
Image copyright belongs to the paper’s original authors. License: CC BY 4.0.
Source Paper
Xiao S, He Y. (2019). Application of Near-infrared Spectroscopy and Multiple Spectral Algorithms to Explore the Effect of Soil Particle Sizes on Soil Nitrogen Detection. Molecules 24(13). https://doi.org/10.3390/molecules24132486
Contact Us
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VISPEK products shown for illustration; these were not the devices used in the cited study.