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In early 2026, the transition toward Integrated Nutrient Management (INM) in rice systems has focused on the “Optimal Substitution Ratio.” Research published in the Agronomy Journal (2025) and related high-impact studies (MDPI Agronomy, Frontiers) highlights that replacing a specific portion of chemical nitrogen with organic sources significantly improves Nitrogen Use Efficiency (NUE) and environmental sustainability.
🌾 1. The 20% “Sweet Spot” for Yield and Efficiency
A landmark two-year study published in Agronomy (June 2025) identified the OR20 treatment (20% organic fertilizer + 80% chemical fertilizer) as the most effective strategy for modern rice cultivars like Shendao47.
- Yield Increase: This specific ratio improved grain yield by 1–10% by increasing effective panicles and grain filling.
- Peak Efficiency: Agronomic N use efficiency (NAE), partial factor productivity (NPFP), and physiological N use efficiency (NPE) all peaked at the 20% substitution level.
- Diminishing Returns: Increasing organic substitution beyond 30% often led to a decrease in yield because the nitrogen release from organic sources was too slow to meet the crop’s demand during the critical tillering stage.
🧬 2. Physiological and Soil Improvements
Organic substitution doesn’t just feed the plant; it alters the soil environment to make chemical nitrogen work harder.
- N Harvest Index (NHI): Studies found that NHI (the ratio of grain N to total plant N) actually increases as organic substitution rises, peaking at 30%. This suggests that organic amendments help the plant mobilize nitrogen into the seeds more effectively.
- Soil Structural Health: Research from Frontiers in Plant Science (2025) showed that partial substitution significantly increased Soil Organic Carbon (SOC) and reduced soil acidification.
- Microbial Activation: The addition of organic matter triggers Nitrogen-related enzyme activity, which facilitates a more stable, slow-release supply of nutrients throughout the growth cycle.
🌍 3. Environmental Benefits: The “Win-Win” Strategy
One of the most significant findings in late 2025 and early 2026 is the impact of substitution on greenhouse gas emissions.
| Metric | Impact of Partial Substitution (2025 Data) |
| Nitrous Oxide ($N_2O$) | Decreased by 17–20% compared to 100% chemical N. |
| Ammonia Volatilization | Reduced by 56–87% (highly effective for air quality). |
| Methane ($CH_4$) | Complex: Organic fertilizer alone increases $CH_4$ by up to 400%, but combined with urea, emissions are reduced by 40–48% compared to pure organic plots. |
| Carbon Sequestration | 50% substitution inhibited SOC mineralization, improving long-term storage. |
🧪 4. New Technology: Biochar-Based Substitution
As of November 2025, the “next generation” of substitution involves Biochar-based organic fertilizers (BF).
- Yield Performance: While conventional organic substitution (CF) at 30% increased yields by 8.9%, Biochar-based substitution (BF) at the same 30% rate increased yields by 14.2%.
- Cooking Quality: BF treatments significantly enhanced the peak viscosity and breakdown value of the rice, improving its texture and market value.
