Complete guide to interpreting soil test results from IARI, NABL-accredited labs, soil health cards, and state agriculture department reports. Understand what each value means and what fertilizer action to take.
Soil pH measures acidity or alkalinity on a scale of 0–14. pH 7 is neutral. Below 7 is acidic; above 7 is alkaline. Indian soils range from pH 4.5 (acidic laterite soils in Kerala/Assam) to pH 9.5 (sodic black cotton soils in Maharashtra).
| pH Range | Soil Type | Common in India | Recommended Action |
|---|---|---|---|
| <5.5 | Strongly Acidic | Kerala, Assam, West Bengal hills | Apply agricultural lime 2–4 t/ha; use ammonium-based fertilizers sparingly |
| 5.5–6.5 | Slightly Acidic | Deccan plateau, Eastern India | Optimal for most crops; no pH correction needed |
| 6.5–7.5 | Neutral | Alluvial plains (Punjab, Haryana, UP) | Ideal pH range; no correction needed |
| 7.5–8.5 | Alkaline | Rajasthan, Gujarat, Madhya Pradesh | Apply gypsum 500–1000 kg/ha; use acid-forming fertilizers (ammonium sulphate) |
| >8.5 | Sodic/Highly Alkaline | Black cotton soils, Maharashtra | Gypsum reclamation + pyrite application + organic matter; consult soil scientist |
EC measures total dissolved salts in soil. High EC indicates salinity stress that reduces water uptake by plants. Normal EC for crop production: less than 1.0 dS/m. EC above 4.0 dS/m affects sensitive crops severely.
| EC (dS/m) | Salinity Level | Effect on Crops | Action |
|---|---|---|---|
| <1.0 | Non-saline | No restriction | No action needed |
| 1.0–2.0 | Very Slightly Saline | Slightly sensitive crops affected | Leaching irrigation before sowing |
| 2.0–4.0 | Slightly Saline | Many crops affected | Leaching + select tolerant varieties |
| 4.0–8.0 | Moderately Saline | Only tolerant crops viable | Gypsum + leaching + organic matter |
| >8.0 | Highly Saline | Only highly tolerant crops viable | Major reclamation needed — consult expert |
Organic carbon is the most important soil health indicator. Indian soils are critically low in organic carbon — average OC is 0.5% against a desirable level of 1.5–2.0%. OC drives soil biology, water holding capacity, nutrient cycling, and structure.
| OC Level (%) | Rating | Interpretation | Recommendation |
|---|---|---|---|
| <0.5 | Very Low | Critical deficiency — poor soil health | FYM 10–15 MT/ha, vermicompost 3 MT/ha, green manure crops |
| 0.5–0.75 | Low | Below optimal — common in Indian soils | FYM 7–10 MT/ha annually, reduce burning of crop residues |
| 0.75–1.0 | Medium | Acceptable, improving trend needed | FYM 5 MT/ha + biostimulants, maintain crop residue |
| >1.0 | High | Good soil health — maintain | Continue organic inputs, avoid over-tillage |
| Nutrient | Low | Medium | High | Unit |
|---|---|---|---|---|
| Available Nitrogen (N) | <280 | 280–560 | >560 | kg N/ha |
| Available Phosphorus (P₂O₅) | <22 | 22–44 | >44 | kg P₂O₅/ha |
| Available Potassium (K₂O) | <150 | 150–300 | >300 | kg K₂O/ha |
When nitrogen is LOW: increase urea/ammonium nitrate application by 25%. When phosphorus is LOW: increase SSP/DAP by 30%. When potassium is LOW: add MOP/SOP. When levels are HIGH: reduce corresponding fertilizer by 30–50% to save costs and prevent luxury consumption.
| Micronutrient | Deficient < | Adequate > | Deficiency Symptoms |
|---|---|---|---|
| Zinc (Zn) | 0.6 ppm | 1.0 ppm | White stripe disease, small leaves, interveinal chlorosis |
| Iron (Fe) | 4.5 ppm | 5.0 ppm | Young leaf yellowing (interveinal), common in alkaline soils |
| Manganese (Mn) | 2.0 ppm | 5.0 ppm | Interveinal chlorosis with green veins, grey speck in oats |
| Copper (Cu) | 0.2 ppm | 0.4 ppm | Bluish-green wilting leaves, dieback of shoot tips |
| Boron (B) | 0.5 ppm | 1.0 ppm | Hollow heart, poor fruit set, crinkled terminal leaves |
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