“A soil test report has no value until it is translated into the right fertilizer dose.”
This blog explains what happens after soil testing, how fertilizer doses are adjusted, the earlier recommendation approach, and how NARC has updated the fertilizer recommendation model to make nutrient management more precise and practical.
Introduction
Soil testing does not end with a laboratory report, it begins the most important step in nutrient management: fertilizer dose adjustment. Once soil nutrient status is known, fertilizer recommendations are fine-tuned to match the soil’s existing fertility, crop demand, and field conditions. This process ensures efficient fertilizer use, cost savings for farmers, and protection of soil and the environment.
Why Fertilizer Adjustment After Soil Testing Matters
Applying a uniform fertilizer dose to all fields ignores soil variability and often leads to:
- Over-fertilization in fertile soils
- Under-fertilization in poor soils
- Higher production costs
- Nutrient losses and environmental pollution
Soil-test-based fertilizer adjustment ensures that nutrients are applied only where and when they are needed.
“Balanced fertilization starts with knowing what the soil already has.”
What Happens After a Soil Test?
After soil analysis, nutrients such as Nitrogen (N), Phosphorus (Pâ‚‚Oâ‚…), and Potassium (Kâ‚‚O) are categorized into classes such as Very low, Low, Medium, High, and Very high and so on as per the national government guidelines.
Based on these categories, fertilizer doses are adjusted from the general recommended dose for a crop.
Approaches of Fertilizer Adjustment
Traditional Approach
Before the recent revision, fertilizer recommendations in many programs followed a simpler adjustment rule based on soil test category:
Low Nutrient Status
100% of recommended dose.
Medium Nutrient Status
50% of recommended dose
High Nutrient Status
25% of recommended dose
This approach helped reduce fertilizer use in fertile soils but had limitations:
- Same adjustment for all soil types
- Limited differentiation between nutrients
- Less responsive to varying soil conditions
"“The old system reduced fertilizer use, but precision was limited.”"
Modern Approach
To improve precision and nutrient use efficiency, NARC has revised the fertilizer recommendation model, introducing a more graded and soil-sensitive approach. Instead of a single reduction rule, fertilizer doses are now adjusted based on Nutrient status category, Soil type (light or heavy), Specific nutrients (N, Pâ‚‚Oâ‚…, Kâ‚‚O).
| Nutrient Status/Category | Soil types | Fertilizer Dose Recommended | ||
|---|---|---|---|---|
| Nitrogen (N) | Phosphorus (P2O5) | Potassium (K2O) | ||
| Very low | All | 125 % of N | 125% of P2O5 | 125 % of K2O |
| Low and Medium | All | 100 % of N | 100% of P2O5 | 100% of K2O |
| High | Light | 80 % of N | 70% of P2O5 | 70% of K2O |
| High | Heavy | 75 % of N | 60% of P2O5 | 60% of K2O |
| Very High | All | 25 % of N | 25% of P2O5 | 25% of K2O |
| Rainfed condition | Rainfed condition | 80 % of calculated nutrients | ||
“Precision in fertilizer recommendation begins after the soil test not before.”
Example
Let us assume the following:
Soil Test values: N = Low, Pâ‚‚Oâ‚… = High, Kâ‚‚O = Very High
Soil Texture: Light
General Recommended Dose for Maize OPV (Eastern Domain): N = 130 kg/ha, Pâ‚‚Oâ‚… = 60 kg/ha, Kâ‚‚O = 40 kg/ha
Using the new adjustment model:
N Dose = 100% of 130 = 130 kg/ha
Pâ‚‚Oâ‚… Dose (Light Textured soil)= 70% of 60 = 42 kg/ha
Kâ‚‚O Dose = 25% of 40 = 10 kg/ha
Adjusted Fertilizer New Dose: N = 130 kg/ha, Pâ‚‚Oâ‚… = 42 kg/ha, Kâ‚‚O = 10 kg/ha
Thus, fertilizer is now calculated from NPK = 130:42:10 kg/ha instead of 130:60:40 kg/ha.
Conclusion
Soil testing is only the first step; fertilizer dose adjustment is where real benefits are realized. While the earlier system relied on broad reductions, the updated NARC fertilizer recommendation model introduces a more refined, soil- and nutrient-specific approach.
By adopting soil-test-based fertilizer adjustment, farmers and advisors can achieve higher nutrient use efficiency, sustainable yields, and healthier soils, ensuring that fertilizers work with the soil—not against it.
“Right rate, Right method, Right source, Right time : fertilizer efficiency begins after the soil test."