Micronutrient & Diagnose & Correct

Compare your soil-test value against the published critical limit for that nutrient and extractant. The widely used limits are DTPA-Zn 0.6 ppm, DTPA-Fe 4.5 ppm, DTPA-Mn 2.0 ppm, DTPA-Cu 0.2 ppm, hot-water B 0.5 ppm, available Mo 0.10 ppm and available S 10 ppm. Below the limit the nutrient is deficient and a yield response is likely; just above it the value is marginal; well above it the nutrient is sufficient and no correction is needed.

Fix the nutrient that is both furthest below its critical limit and most important to your crop. This tool ranks them for you: it weights how far each value sits below the limit by your crop's sensitivity to that nutrient, then puts the most yield-limiting one at the top. Correcting that one first gives the biggest return before you spend on the others.

The standard soil dose is about 25 kg/ha of zinc sulphate heptahydrate (21% Zn), which supplies roughly 5.25 kg of actual zinc per hectare, broadcast and incorporated before sowing. For a standing crop you can rescue it with a 0.5% foliar spray — about 2.5 kg of zinc sulphate dissolved in 500 litres of water per hectare. The calculator shows both the soil rate and the foliar spray for whichever nutrients are deficient.

About 10 kg/ha of borax (11% B) supplies roughly 1.1 kg of boron per hectare. Boron has a narrow margin between deficiency and toxicity, so apply it evenly and do not exceed the recommended rate. For a quick correction on a sensitive crop such as cotton or oilseeds, a 0.2% foliar spray works; the tool gives the exact product weight per spray.

Deficient means the value is below the critical limit, where most crops show a clear yield response to correction. Marginal is the band just above the critical limit — typically up to about 1.5 times the limit — where a response is uncertain and only sensitive crops are likely to benefit. On a marginal reading a foliar spray is often the cheapest insurance; an outright soil application is usually reserved for deficient readings.

Because yield is set by the most limiting nutrient, and treating one nutrient while another is more deficient wastes money. Most calculators handle a single nutrient in isolation. This one reads your whole Zn, Fe, Mn, Cu, B, Mo and S panel, classifies every nutrient against its critical limit, and ranks them so you correct the real constraint first rather than the one you happened to test.

The critical limits are largely crop-independent, but crop sensitivity is not. Rice and citrus are highly sensitive to zinc and iron, wheat to zinc and manganese, pulses to molybdenum and boron, and oilseeds to sulphur and boron. The tool uses a crop-sensitivity matrix so the fix-first ranking reflects what your specific crop responds to, not a generic order.

Soil application before sowing builds the level for the season and suits a clear deficiency; it is the default for zinc, boron and sulphur. Foliar sprays act fast and are ideal for rescuing a standing crop or topping up a marginal reading, especially for iron and manganese, which can be locked up in alkaline soils. The calculator gives both the soil rate in kg/ha and the foliar concentration and spray volume.

For a mild or marginal deficiency, often yes — one or two well-timed foliar sprays can carry a crop through. For a strong deficiency a foliar spray relieves symptoms but does not rebuild the soil reserve, so combine it with a soil application before the next crop. The tool flags which nutrients are deficient versus marginal so you can choose accordingly.

Available sulphur below about 10 ppm (by the 0.15% calcium-chloride method) is considered deficient, and 10 to 15 ppm is marginal. Sulphur deficiency is common in oilseeds and pulses and in intensively cropped soils that no longer receive sulphur-containing fertilizers. Gypsum at around 130 kg/ha or single super-phosphate are common corrective sources; the calculator includes sulphur in the panel.

They are the standard ICAR and state soil-testing-laboratory limits used across Indian and many international advisory systems, and they are reliable for screening. Local calibration can shift a limit slightly, and severe pH or organic-matter extremes change nutrient availability. Treat the diagnosis as a sound screen and confirm with your local lab or extension service before large-scale application.

Yes. Boron in particular has a narrow window between deficiency and toxicity, and excess zinc, copper or manganese can induce other deficiencies or harm soil organisms. That is why the tool gives defined, package-of-practice rates rather than open-ended doses, and why you should not stack corrective applications without re-testing. Apply the recommended rate, then verify with a follow-up soil test.