“Soil test numbers gain meaning only when they are placed into the right fertility class.”
This blog explains how soil test values are categorized, why these categories matter.
Introduction
A soil test report often looks complicated filled with numbers, units, and parameters. However, the real value of soil testing lies in interpreting these numbers correctly. To make soil test results useful for fertilizer recommendation and soil management, laboratory values are classified into Very Low, Low, Medium, High, and Very High categories.
Why Soil Test Classification Is Necessary
Soil nutrients behave differently across soils, climates, and land-use systems. A single numerical value cannot directly tell whether a soil is deficient or sufficient. Classification helps to:
- Identify nutrient deficiencies and excesses
- Guide fertilizer dose adjustment
- Standardize recommendations across regions
- Support balanced and sustainable nutrient management
“Classification converts soil chemistry into agronomic action.”
Major Soil Fertility Categories
Each soil parameter is grouped into the following classes:
- Very Low – severe deficiency, strong crop response expected
- Low – deficiency likely
- Medium – marginal to adequate
- High – sufficient, limited response
- Very High – excess, risk of imbalance or loss
These classes form the foundation of soil-test-based fertilizer recommendations.
Category Class of Nutrients
| S.N. | Soil Parameters | Unit | Very Low | Low | Medium | High | Very High |
|---|---|---|---|---|---|---|---|
| 1 | Total Nitrogen (Hill) | % | <0.05 | 0.05-0.1 | 0.1-0.2 | 0.2-0.4 | >0.4 |
| 2 | Total Nitrogen (Terai) | % | <0.03 | 0.03-0.07 | 0.07-0.15 | 0.15-0.25 | >0.25 |
| 3 | Available Phosphorus (Hill) | kg/ha | <10 | 10-30 | 30-55 | 55-110 | >110 |
| 4 | Available Phosphorus (Terai) | kg/ha | <11 | 11-28 | 28-56 | 56-112 | >112 |
| 5 | Available Potassium (Hill) | kg/ha | <55 | 55-110 | 110-280 | 280-504 | >504 |
| 6 | Available Potassium (Terai) | kg/ha | <55 | 55-110 | 110-280 | 280-500 | >500 |
| 7 | Organic Matter (Hill) | % | <1 | 1-2.5 | 2.5-5 | 5-10 | >10 |
| 8 | Organic Matter (Terai) | % | <0.75 | 0.75-1.5 | 1.5-3 | 3-5 | >5 |
| 9 | Exchangeable Calcium | Meq/100g | <5 | 5-10 | >10 | ||
| 10 | Exchangeable Magnesium | Meq/100g | <0.5 | 0.5-1.5 | >1.5 | ||
| 11 | Available Sulphur | ppm | <3 | 3-7 | 7-12 | 12-17 | >17 |
| 12 | Available Boron | ppm | <0.4 | 0.4-0.7 | 0.7-1.2 | 1.2-2 | >2 |
| 13 | Available Zinc | ppm | <0.5 | 0.5-1 | 1-3 | 3-6 | >6 |
| 14 | Available Iron | ppm | <5 | 5-10 | 10-16 | 16-25 | >25 |
| 15 | Available Copper | ppm | <0.3 | 0.3-0.8 | 0.8-1.2 | 1.2-2.5 | >2.5 |
| 16 | Available Manganese | ppm | <4 | 4-8 | 8-12 | 12-30 | >30 |
“Healthy soil must be fertile and safe.”
Conclusion
Soil test classification transforms raw laboratory values into meaningful fertility classes that guide nutrient management decisions. The above critical ranges ensure uniform interpretation across regions and crops, helping farmers apply the right nutrient, at the right rate, in the right soil.
Understanding these categories empowers farmers, technicians, and advisors to move from numbers to knowledge—and from knowledge to sustainable action.
“Good soil management begins with correct interpretation.”