Stable Isotopes Reveal Rapid Cycling of Soil Nitrogen after Manure Application
Bibliographic record
Abstract
Understanding the fate of applied nitrogen (N) in agricultural soils is important for agronomic, environmental, and human health reasons, but it is methodologically difficult to study at the field scale. Natural abundance stable isotope measurements (δ15N) were used in this field study with micrometeorological measurements of nitrous oxide (N2O) emissions to identify the biogeochemical processes responsible for rapid N transformations immediately after application of liquid dairy manure. Fifteen samplings occurred between 16 Mar. 2012 and 5 Apr. 2013, with a focus on spring manure application (before and after) and a winter snowmelt period. Concentrations and δ15N values of ammonium (NH4+), nitrate (NO3−), N2O, and total N were measured throughout the year. Approximately 56 (±7)% of the NH4+–N applied in the spring could not be accounted for 3 d after manure application and was presumably lost by ammonia volatilization before it was tilled into the soil and/or removed from the inorganic N pool by microbial assimilation. Almost all of the remaining manure‐NH4+ (95 ± 1.1%) was converted within 3 wk to NO3− and N2O by nitrification and nitrifier‐denitrification, respectively. The in situ 15N isotope effect for nitrification (εNitrate–Ammonium) was calculated to be −32.0 (±5.3)‰. Overall, field‐scale measurements of δ15N at natural abundance provided valuable information that was used to distinguish sources of NH4+ (manure vs. soil organic N) and to follow the production and consumption of NO3− and the pathways of N2O production in soil. Core Ideas 49 to 63% of the manure‐NH4+ was volatilized, assimilated, or fixed 3 d after application. Only 4 to 6% of the manure‐NH4+ remained in the soil 3 wk after application. In situ 15N isotope effect for nitrification (ammonium–nitrate) was −32.0 (±5.3)‰. N2O emissions after manure application were produced by nitrifier‐denitrification. The δ15N values showed active production and consumption of NO3− during winter thaw.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| 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 | 0.000 |
| 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) | 0.001 | 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 source (direct Gemma or distilled Codex), 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".