Organic Fertilizer Substitution and Nitrogen efficiency in Rice production systems (Agronomy Journal, 2025).

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.

🧪 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.