Verra VCS VM0042 v2.2 · IPCC 2019 Tier 1 N₂O · IPCC 2006 SOC · Ex-ante scenario analysis
| Step / Parameter | Baseline | A | B | C | Unit |
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| Step / Parameter | Baseline | A | B | C | Unit |
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| Metric | Corn | Wheat | Rotation Avg |
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Direct and indirect N₂O is modeled under different water and fertilization regimes, following Approach 3 in the VM0042 protocol. The transition from flood to drip reduces waterlogging frequency, shifting production from denitrification-dominated to nitrification-dominated pathways, generally lowering total emissions [1]. In this study, the switch from flood/furrow/sprinkler to surface drip irrigation and sub-surface drip irrigation (SDI) were modeled under various rotation scenarios.
Although the literature provides more precise emission factors (EFs) for flood-irrigated maize [2] and comparative analyses across irrigation systems and crop types [3], no study has explicitly evaluated EFs across comparable drip- and flood-irrigated maize scenarios. To ensure methodological consistency and avoid double counting, the IPCC default EF for all N inputs in dry climates [4], set at 0.005, is applied uniformly across all scenarios.
Indirect N₂O emission factors for atmospheric deposition (EF₄ = 0.010 kg N₂O-N kg⁻¹ NH₃-N) and leaching (EF₅ = 0.011 kg N₂O-N kg⁻¹ N leached) were adopted from IPCC (2019) Tier 1 defaults and held constant across all irrigation scenarios [4]. These factors represent biogeochemical processes occurring after reactive nitrogen leaves the field boundary — atmospheric redeposition and denitrification in receiving water bodies, respectively — and are therefore independent of on-farm irrigation management. Therefore, no scenario-specific adjustment was applied.
For the FracLEACH parameter, the IPCC default value of 0.24 [4] is applied in the baseline scenario. Empirical evidence from maize production systems under semi-arid conditions indicates that drip irrigation reduces nitrogen losses via leaching by approximately 33% compared to flood irrigation [5]. This reduction factor is therefore applied, resulting in an assumed FracLEACH value of 0.16 for drip irrigation. Due to the lack of differentiated data, the same value is also used for the SDI scenario. Furthermore, as the referenced study reports no significant difference in NH₃ volatilization between irrigation methods, FracGASF,urea and FracGASF,DAP are assumed to remain at their IPCC default values of 0.15 and 0.08, respectively, across all scenarios.
References
[1] Gültekin, R., Avağ, K., Görgiişen, C., Öztürk, Ö., Yeter, T. & Bahçeci Alsan, P. (2023). Effect of deficit irrigation practices on greenhouse gas emissions in drip irrigation. Scientia Horticulturae, 310, 111757.
[2] Franco-Luesma, S., Lafuente, V., Alonso-Ayuso, M., Bielsa, A., Kouchami-Sardoo, I., Arrúe, J.L. & Álvaro-Fuentes, J. (2022). Maize diversification and nitrogen fertilization effects on soil nitrous oxide emissions in irrigated Mediterranean conditions. Frontiers in Environmental Science, 10, 914851.
[3] Cayuela, M.L. et al. (2017). Direct nitrous oxide emissions in Mediterranean climate cropping systems: Emission factors based on a meta-analysis of available measurement data. Agriculture, Ecosystems & Environment, 238, 25–35.
[4] Baasansuren, J. et al. (2019). 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories. IPCC, Switzerland.
[5] Di, Y., Gao, Y., Yang, H., Yan, D., Tang, Y., Zhang, W., Hu, Y. & Li, F. (2024). Cutting carbon and nitrogen footprints of maize production by optimizing nitrogen management under different irrigation methods. Frontiers in Plant Science, 15, 1476710.
Click a region to set SOC_REF. Values = OCS 0–30 cm (t C/ha) from SoilGrids REST API (ISRIC, 2024).
| Factor | Value | Note |
|---|---|---|
| FLU — Land use (annual cropland) | 1.00 | Cropland remaining cropland [IPCC 2006, Table 5.4] |
| FI_baseline — Input factor (flood) | 1.00 | Medium residue, no manure [Table 5.6, warm dry] |
| FI_project — Input factor (drip) | 1.11 | High residue (optimised fertigation → better yield → more residue) [Table 5.6] |
| FMG_baseline — Full tillage (flood) | 1.00 | Full tillage = 1.00 [Table 5.5, warm dry] |
| FMG_ScenA — Surface drip | 1.00 | No tillage change with surface drip lines |
| FMG_ScenC — SDI (no-till) | 1.10 | SDI buried lines → no-till feasible → FMG_no-till [Table 5.5] |
| Transition period | 20 yr | Default: 20 years to new SOC equilibrium [IPCC 2006 §2.3.3.1] |
| C→CO₂ conversion | 44/12 = 3.667 | Molecular weight ratio CO₂/C |
| Parameter | Baseline | A | B | C | Unit |
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| Component | Scen A | Scen B | Scen C | Unit |
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| Metric | Scen A | Scen B | Scen C | Unit |
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| Metric | Scen A | Scen B | Scen C |
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Her bölgenin SOC ölçüm saati kendi enrollment yılından başlar. Sonradan katılan çiftçiler mevcut SOC birikimini devralmaz — 20 yıllık SOC geçiş süreci sıfırdan başlar.
| Bölge / Faz | Başlangıç Yılı | Başlangıç Çiftlik | ha/çiftlik₀ | +Çiftlik/yıl | Max Çiftlik | ha Büyüme %/yıl | Max ha/çiftlik |
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| Scenario A | Scenario B | Scenario C | Scenario D | |
|---|---|---|---|---|
| SOC / N₂O approach | App 1 + App 1 | App 2 + App 1 | App 1 + App 3 | App 2 + App 3 |