Reading the Soil Health Card the right way
India's Soil Health Card scheme has issued more than 23 crore cards since 2015 — one for every operational holding. The card prints twelve parameters: pH, EC, organic carbon, available N (KMnO₄ method), available P (Olsen-P for alkaline, Bray-P for acid), available K (1N NH₄OAc), and the micronutrients S, Zn, B, Cu, Fe, Mn. Each value carries a "low / medium / high" label set by ICAR-IISS Bhopal's rating chart. The chart, formalised in Subba Rao & Sammi Reddy (2008) and updated for SHC 3.0 in 2023, is the input this interpreter implements.
Most farmers receive the card, glance at the colour-coded labels, and file it. That is a wasted asset. Read in conjunction with a yield target and a recommended-package, the SHC tells you exactly how much N, P, K, FYM, lime or gypsum to apply — and where to stop. This page summarises the rating logic and links each rating to a concrete action.
Nitrogen rating: KMnO₄-extractable N (kg/ha)
ICAR-IISS thresholds: < 280 kg/ha is "low", 280-560 is "medium", > 560 is "high". The all-India median in SHC aggregate dashboards is ~265 kg/ha — so the majority of Indian fields rate low. Low-N soils respond strongly to applied urea: the standard wheat dose 120 kg N/ha is justified. High-N soils (rare; bhabhar zones, recent FYM history) need only 60-80 kg/ha to avoid lodging. The STCR calculator does this adjustment automatically.
Phosphorus rating: Olsen-P or Bray-P (kg/ha)
< 10 kg/ha is low, 10-25 is medium, > 25 is high. Indian soils are systemically low in P because of Fe-Al immobilisation in acid soils and Ca-immobilisation in alkaline soils. Low-P fields demand 50-60 kg P₂O₅/ha at sowing (band-placed DAP) for cereals; high-P fields can skip P for one season. P moves slowly so build-up over time is durable.
Potassium rating: NH₄OAc-K (kg/ha)
< 108 kg/ha low, 108-280 medium, > 280 high. Punjab and Haryana alluvial soils tend to test "high" because of K-rich micaceous parent material — but this is misleading: NH₄OAc extracts non-exchangeable K too, and K-mining over decades is real. Andhra Pradesh black soils generally test low. K is essential for tuber crops (potato), fruiting (banana, mango), and stress resistance.
Organic carbon: the most important number
OC < 0.5% is low, 0.5-0.75% medium, > 0.75% high. ICAR-IISS calls OC the "master soil quality variable" — it correlates with water-holding capacity, microbial activity, aggregate stability, and N mineralisation. The PM-PRANAM scheme uses OC level as a key incentive trigger. Low-OC soils need 7.5-10 t/ha FYM (use the FYM calculator); the rebuild takes 3-5 years.
pH: the master driver of nutrient availability
pH < 5.5 = acidic — P, Mo, Ca, Mg locked; Al, Mn toxic. Lime is the correction. pH 5.5-7.5 = the optimal range for most crops. pH 7.5-8.5 = alkaline normal — common in arid soils; micronutrient (Fe, Zn, B) availability begins to drop, supplement foliar. pH > 8.5 = sodic — gypsum + drainage required (see Gypsum calculator).
EC: salinity in the root zone
EC < 1 dS/m = normal. 1-2 = slightly saline; tolerant varieties (KRL-210 wheat, CSR-30 paddy, dhaincha for green manure) advised. > 2 = saline; only halophytes (suaeda, salicornia) or specialised salt-tolerant cultivars succeed without leaching. Salinity is a coastal-belt and arid-irrigation issue — Gujarat coastal Saurashtra, Tamil Nadu Cauvery delta, Karnataka Tungabhadra command.
Worked example: northern UP smallholder
Soil test: N 240, P 8, K 150, OC 0.42, pH 7.8, EC 0.5. Calculator rating: N low, P low, K medium, OC low, pH normal, EC normal. Resulting advice: apply full N (120 kg/ha for wheat) via urea + DAP; ensure 50 kg P₂O₅/ha basal because P is low; supplement with 10 t/ha FYM to rebuild OC over 3 years; no lime / gypsum needed because pH is normal and EC is fine. Combine with the STCR NPK calculator for precise dose and the NPK Bag Converter to translate kg to bags.
Secondary and micronutrients
The SHC also reports S, Zn, B, Cu, Fe, Mn ratings. Sulphur is increasingly limiting in oilseed-growing states because of NPK-only fertilisation (mustard and soybean need 20-30 kg S/ha; supply through SSP, ammonium sulphate or gypsum). Zinc is the most commonly deficient micronutrient (45% of Indian samples test low) — basal 5 kg ZnSO₄/ha for paddy is standard. Boron deficiency is the silent yield-cutter in cauliflower, cabbage, mustard; foliar 0.2% borax at flowering corrects it.
How to use this calculator
Type your six SHC values into the widget; the rating and advice update instantly. Print the result or screenshot for your records. Use the linked STCR NPK calculator for precise fertiliser dose, the Lime or Gypsum calculators if pH is out of range, and the FYM calculator if OC is low. Repeat the soil test every three years to track improvement — labels should move "low → medium → high" if your management is right.
Sources
ICAR-IISS Bhopal Soil Test Rating Charts for Indian Soils (Subba Rao, Sammi Reddy 2008, updated 2023); Soil Health Card 3.0 operational guidelines 2024; ICAR-AICRP on Micronutrients Annual Report 2023-24; ICAR-CSSRI Karnal sodicity rating chart 2024.