Nitrogen‐15 and Oxygen‐18 Natural Abundance of Potassium Chloride Extractable Soil Nitrate Using the Denitrifier Method
Bibliographic record
Abstract
In agroecosystems, most isotopic investigations of NO 3 − involve the use of tracers that are artificially enriched in 15 N. Although the dual isotope composition of NO 3 − — δ 15 N and δ 18 O is especially beneficial for understanding the origin and fate of NO 3 − , its use for KCl‐extractable soil NO 3 − has been hampered by the lack of a suitable analytical technique. Our objective was to test whether the denitrifier method, whereby NO 3 − is reduced to N 2 O before mass spectrometric analysis, can be used to determine the N and O isotopic composition of NO 3 − from 2 M KCl soil extracts. Several internationally accepted NO 3 − standards were dissolved in 2 M KCl, the conventional extractant for soil inorganic N, and inoculated with the bacterial strain Pseudomonas aureofaciens (ATCC no. 13985). The standard deviation of the NO 3 − standards analyzed did not exceed 0.2‰ for δ 15 N and 0.3‰ for δ 18 O values. After appropriate corrections, differences between our measured and consensus δ 15 N and δ 18 O values of standard NO 3 − generally were within the standard deviations given for the consensus values. Both δ 15 N and δ 18 O values were reproducible among separate analytical runs. The method was also tested on genuine 2 M KCl extracts from unfertilized and fertilized soils. Depending on N fertilization, the soils had distinct δ 15 N and δ 18 O values, which were attributed to amendment with NH 4 NO 3 fertilizer. Hence, our data indicate that the denitrifier method provides a fast, reliable, precise, and accurate way of simultaneously analyzing the natural abundances of 15 N and 18 O in KCl‐extractable soil NO 3 −
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How this classification was reachedexpand
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 | 0.003 | 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 | 0.001 | 0.002 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".