Chemical properties of organic amendments influence nitrous oxide emissions from agricultural soils
Bibliographic record
Abstract
Prediction of organic amendment's (OA) potential to emit soil nitrous oxide (POA-N2O) is difficult because of the variable composition of OAs and of complex interactions with soil properties and environmental conditions. The objectives of this thesis were (1) to conduct a meta-analysis of in-field N2O emissions following OA application to agricultural soils to assess the global emission factor (EF) for all organic sources (EForg) and its modulation by environmental and management-related factors; (2) to determine how experimental conditions affect the POA-N2O and select optimal conditions for laboratory-based assessment; (3) to measure the immediate (P1), short- (P2) and medium-term (P3) POA-N2O with the selected laboratory-based incubation method and then, relate P1, P2, and P3 to the physico-chemical characteristics of more than 131 OAs. The meta-analysis conducted on 256 EFs from 43 sites in 12 countries yielded an EForg equal to 0.57 ± 0.30%, which is lower than the IPCC default EF of 1% for synthetic fertilizer (SF). Three groups of OAs with similar EFs were identified: the high-risk group including animal manures, waste waters and biosolids (1.09 ± 0.17%); the medium-risk group including composts with fertilizers and crop residues with fertilizers (0.46 ± 0.22%); and the low-risk group including composts, crop residues, paper mill sludge and pellets (0.25 ± 0.20%). The EF was modulated by the C/N ratio of the OA, soil properties and precipitation. The EFs were on average 2.8 times greater in fine-textured soils than coarse-textured soils. The comparative incubation study showed that O2-limited conditions in headspace of a sealed-jar system increased the magnitude of N2O fluxes by 1.1 to 2.3-fold compared to open-jar systems. Intermittent aerations of a sealed-jar system relying on repeated measurement periods was then selected to assess P1 (48h), P2 (2nd wk), and P3 (3rd wk). In O2-limited conditions created in a Kamouraska clay soil, maximum P1 was reached for crop residues (CR) with C/N ratio < 15 and liquid manure. Liquid manure (LM) P1 was five-fold greater than solid manure (SM) P1, whereas P2 and P3 were higher in SM- than in LM-amended soils. Physico-chemical properties of OAs explained 23%, 27%, 27%, 56%, and 60% of the variability in P1 response for SM, LM, vegetal compost, poultry manure and CR, respectively. P1 was correlated to the concentrations of water-extractable organic C and volatile fatty acids, NO3-, NH4+, S, equivalent alkalinity and pH of OAs (P < 0.05). In contrast, none of those chemical characteristics were correlated to P2 and P3, suggesting that the increased N2O emissions supported by the OA-C and N substrates occurred within 48 h of adding these OAs to soil. Further investigations are necessary to test the influence of other specific conditions, e.g., soil texture, water content, OA application techniques on POA-N2O and their interactions with OA properties.
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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 | 0.003 | 0.003 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.003 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 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 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".