Fourier Transform Infrared, UV-Visible, and X-Ray Diffraction Analyses of Organic Matter in Humin, Humic Acid, and Fulvic Acid Fractions in Soil Exposed to Elevated CO <sub>2</sub> and N Fertilization
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Bibliographic record
Abstract
FT-IR, UV-visible, and X-ray diffraction analyses were used to investigate the nature of organic matter in three fractions of soil humic substances (humin, HU; humic acid, HA; and fulvic acid, FA) extracted at a depth of 0–10 cm from the soil under rye grass ( Lolium perenne) culture. FT-IR and XRD analyses showed that the extracted HAs still contained the clay matrix, but the extracted FAs, which were purified by adsorption-desorption from a macroreticular nonionic resin, were free from the clay mineral constituents. The data obtained in the present study shed more light on the chemical structure of the HU, HA, and FA fractions in the infrared absorption band region of 400–1000 cm −1 where the assignments of bands are still lacking in the literature. The bands characteristic of organic functional groups, especially benzene rings and condensed aromatics, which were masked by the strong bands of the clay matrix in the HU and HA fractions, were clearly shown in the FA fraction, which was free from the clay mineral constituents. While the UV-visible spectra of HAs and FAs were similar, the E 465 /E 665 ratios of HAs were about three times lower than those of FAs. Amounts of carboxyl groups, determined by titration, were about four times higher in the FA than in the HA fraction, which is in agreement with the FT-IR analysis. The HU, HAs, and FAs fractions extracted from the soil under the same culture and exposed to elevated CO 2 levels (60 Pa pCO 2 ) under different N fertilizer application rates (100 and 420 kg N/ha) were also studied. The results show that there was no significant change in the spectra of HU, HAs, and FAs extracted from soils exposed to elevated CO 2 for 2 years. In contrast, elevated CO 2 combined with a high N fertilization rate resulted in a remarkable increase of the acidic OH groups of the FA.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it