Micronutrient Management in Onion: Zinc, Boron, Sulphur and Other Nutrients, How to Spot a Shortage, and How to Correct It

Zinc, boron and sulphur shortages are common in Indian soils, and ICAR-DOGR reports that micronutrient application raised onion bulb yield by 7 to 15 percent over control. A national ICAR study of 242,827 soil samples found 58.6 percent of Indian soils short in sulphur, 51.2 percent in zinc and 44.7 percent in boron. ICAR-DOGR recommends 15 or 30 kg sulphur per hectare by soil sulphur status, 10 kg zinc sulphate and 10 kg borax per hectare only in deficient areas, and a foliar micronutrient mixture at 45 and 60 days after transplanting where several nutrients are short. Test the soil first, keep soil pH between 6.0 and 7.5, and correct a visible shortage straight away.

It means supplying the small-quantity nutrients, such as zinc, boron, iron, manganese and copper, together with sulphur, on the basis of soil status and crop symptoms. ICAR-DOGR reports that micronutrient application raised onion bulb yield by 7 to 15 percent over control, so a hidden gap in one of them is worth finding.

The ICAR-DOGR guidance is direct. Its Onion Agropedia page says micronutrient application increased bulb yield by 7 to 15 percent over control and that deficiencies found during the crop should be corrected immediately by foliar or soil application. It also says that a field with several shortages needs farmyard manure and a foliar micronutrient mixture. The rest of this post follows that guidance and adds the soil survey data and the trial results behind it.

This post does not repeat the main fertilizer schedule. For nitrogen, phosphorus and potassium splits, see our onion farming in India guide, and for seedlings see the rabi onion nursery schedule. Garlic behaves much the same way; the garlic farming guide covers that crop.

Sulphur is applied in tens of kilograms per hectare, while zinc, boron, iron, manganese and copper are needed in far smaller amounts. DOGR gives the macro removal for a 40 tonne per hectare crop as 90 to 95 kg N, 30 to 35 kg P2O5 and 50 to 55 kg K2O.

Read the uptake figures as what the crop took up in that trial's best treatment, not as a target and not as a dose. The point of the table is the scale: a few hundred grams per hectare of zinc and boron against roughly a hundred kilograms of nitrogen. Because the amount is small, the dose has to come from a soil result and an official rate, not from habit.

Sulphur sits between the two groups: DOGR gives it its own recommendation in kilograms per hectare. The next sections show how common the shortages are before the dose tables.

Very common. An ICAR study of 242,827 surface soil samples from 615 districts in 28 states found that 58.6 percent of soils were short in available sulphur, 51.2 percent in zinc and 44.7 percent in boron, against 19.2 percent for iron, 17.4 percent for manganese and 11.4 percent for copper. Sulphur and zinc together were short in 9.3 percent.

The study was run under the ICAR All India Coordinated Research Project on micro and secondary nutrients, sampled from April to June in 2012 to 2018, and the authors say deficiencies should be re-checked every 3 to 5 years because status changes with crop and soil management. The table below adds up the acute, deficient and latent classes for the main onion states. The sums are ours, from the state tables in the paper.

Source: Shukla et al. 2021, sums of the acute deficient, deficient and latent deficient columns. Two patterns stand out. Sulphur and zinc are short across almost every onion belt. Boron is short in Maharashtra, Gujarat, Bihar, Karnataka and Telangana but mostly adequate in Madhya Pradesh and Rajasthan. That is why a blanket recipe is a poor idea and a soil test is a good one.

For zinc, the authors name low organic carbon, high pH, coarse texture and calcareous soil as the soils where it runs short. For boron they name lateritic and limed acid soils, calcareous soils and leached sandy soils.

These are the critical limits the survey used for Indian soils. They help you read a lab report: the first column is the top of the latent-deficient class, so a result at or below it counts as short. Use the limits printed on your own lab report if they differ. The soil health card guide shows which lines to read.

DOGR recommends sulphur as a basal dose at transplanting: 15 kg S per hectare where soil sulphur is above 25 kg per hectare, 30 kg where it is below, and 50 kg for long-day onion. That is about 6, 12 and 20 kg S per acre (1 ha = 2.47 acres). DOGR notes sulphur matters for yield and pungency.

Source: ICAR-DOGR Agropedia. A source of sulphur has to carry that much elemental S. As arithmetic, not a label dose: a fertilizer with 24 percent sulphur would need about 125 kg per hectare to deliver 30 kg S, and one with 21 percent nitrogen would add about 26 kg N at the same time, which must be counted in the nitrogen plan. The ammonium sulphate fertilizer page lists 21 percent nitrogen and 24 percent sulphur and names onion among its vegetables.

Trials back the practice. At Rajgurunagar, the home of DOGR, a two-season late kharif trial on variety B 780 gave a significant response to sulphur from 30 to 75 kg per hectare over NPK alone, with the highest bulb yield of 39.1 t per hectare at 75 kg S (Qureshi and Lawande). In Mandsaur in rabi 2009-10, 120 kg N with 60 kg S gave the best growth, yield, pyruvic acid and cost-benefit ratio among the levels tested (Jain et al.).

The trial doses are higher than DOGR's soil-based recommendation, because a trial tests a range to find the ceiling. Use the DOGR numbers as your starting point and the trials as evidence that onion responds to sulphur.

Yes. In the Rajgurunagar trial, bulb sulphur content rose by 48.0 percent at 75 kg S per hectare, and at 45 kg S storage losses over six months were 10.4 percent lower than with NPK alone. Storage loss showed a significant negative correlation with pyruvic acid, the measure of pungency, and with total soluble solids.

In plain terms, a more pungent bulb with more soluble solids kept better in that study. That matters for a rabi crop held in a storage structure for months, and it is the strongest practical reason to treat sulphur as a quality nutrient and not only a yield nutrient. The Mandsaur trial also found the highest pyruvic acid content at 120 kg N plus 60 kg S per hectare.

NIPHM's onion package describes zinc shortage as restricted growth, with young leaves turning yellow and pitting between the veins of older leaves, then death of tissue between the veins while the main veins stay green. Its foliar fix is zinc sulphate at 0.5 percent twice, a fortnight apart. DOGR advises 10 kg zinc sulphate per hectare basal in deficient areas.

Cornell's zinc fact sheet lists onions in its high-sensitivity group for zinc deficiency. The ICAR survey links zinc shortage to low organic carbon, high pH, coarse texture and calcareous soil, which is why a high-pH field deserves a zinc test before transplanting. See NIPHM and Cornell Fact Sheet 32.

What the research says about the fix:

• DOGR: 10 kg zinc sulphate per hectare, basal, in zinc-deficient areas (about 4 kg per acre by our conversion). The DOGR page prints the formula as ZnSO with the last digit missing, so it is read here as zinc sulphate.
• Rajasthan rabi trial, 2020-21 and 2021-22: control, 25 kg zinc sulphate per hectare to soil, dipping seedlings in a zinc solubilizer, or foliar zinc sulphate at 0.5 percent at 30 and 45 days after transplanting. Foliar 0.5 percent gave the highest growth and yield, not significantly different from soil application (Choudhary et al.).
• Agra rabi trial: 100 percent NPK plus 5 kg Zn and 1 kg B per hectare gave 32.13 t per hectare against 30.36 t for NPK alone, a gain of 1.77 t or about 5.8 percent by our arithmetic (Singh et al.).
• Bihar kharif trial, 2016: soil zinc sulphate at 25 kg per hectare gave the best benefit-cost ratio of 3.53, and 50 kg per hectare gave the highest net return among ten treatments (Maurya et al.).

The trial treatments are not recommendations, and the soil rates differ because the soils, seasons and zinc sources differ. The DOGR rate is the one printed in this post as the national institute's figure for zinc-deficient soils. If your state agricultural university gives a different rate for your soil, follow your state package.

DOGR recommends 10 kg borax per hectare as a basal dose only in boron-deficient areas, about 4 kg per acre by our conversion. The ICAR survey found boron short in 44.7 percent of Indian soils, mostly in Maharashtra, Gujarat, Bihar, Karnataka and Telangana. Do not apply boron without a soil result.

The survey authors say boron deficiency was higher in lateritic and limed acid soils, calcareous soils and leached sandy soils. No onion-specific boron symptom description from an ICAR, NIPHM or university page could be opened for this post, so none is given here; a soil test is the way to confirm boron.

In the Agra trial, the plots given 1 kg B per hectare produced the highest boron uptake of 392.1 g per hectare, and the combined zinc and boron treatment out-yielded NPK alone.

The practical rule is the same as for sulphur: boron is mostly a soil-status decision. The survey table shows it is short in most soils of Maharashtra, Gujarat, Bihar, Karnataka and Telangana and adequate in most of Madhya Pradesh and Rajasthan. If your result is at or below 0.70 mg per kg, boron is in play.

NIPHM's onion package describes sulphur shortage as general yellowing across the whole plant including young leaves, manganese shortage as tip burn, curling and thick-necked, late-bulbing plants, and iron shortage as yellowing of the youngest leaves that ends in bleached leaves. Sulphur is by far the most widespread of the three in the ICAR survey.

Source: NIPHM AESA-based IPM package for onion. The same package lists zinc, covered in the zinc section. No onion-specific description of copper, calcium or magnesium shortage could be opened from an ICAR, NIPHM or university source, so they are not described here.

From the ICAR survey, iron is short in 19.2 percent of Indian soils, more so in Gujarat, Rajasthan and Maharashtra, mainly because of alkaline soil pH, and manganese in 17.4 percent. Copper is the least short, at 11.4 percent. For an onion grower in the west, iron deserves a thought. For most others, sulphur, zinc and boron come first.

Where several nutrients are suspected together, DOGR's answer is the foliar micronutrient mixture described later in this post; for a confirmed single problem, fix the cause too, such as pH.

Yes, strongly. DOGR gives the best soil pH for onion as 6.0 to 7.5. Below 6.0, trace element deficiencies or aluminium and manganese toxicity can occur. The survey authors link zinc, iron and manganese shortages to high-pH and calcareous soils. Fixing pH often does more than adding a nutrient.

DOGR also gives a salinity limit: yield declines when electrical conductivity of the soil extract is above 4.0 dS per metre, and it says onion is more sensitive to highly acidic, alkaline and saline soils and to waterlogging. On heavy soils it advises organic manure before planting and good field preparation.

Our post on soil pH and nutrient lock explains the mechanism, soil salinity covers the 4 dS per metre problem, and types of soil in India shows which soils tend to which problem. The winter angle is in cold weather and nutrient uptake.

Send a soil sample to a lab and ask for pH, organic carbon, available sulphur, zinc and boron, then compare the result to the critical limits. Take a second sample from a good patch if you see yellow or twisted plants. Treat symptoms as a prompt to test, not as the diagnosis.

1. Sample before transplanting. Take 0 to 15 cm composite samples, the depth used in the ICAR survey.
2. Ask for sulphur, zinc and boron by name. A basic NPK report does not cover them.
3. Read the result against the limits in the table earlier: sulphur 22.5, zinc 0.90, boron 0.70 mg per kg.
4. Check pH and salinity before adding any nutrient; DOGR's range is pH 6.0 to 7.5 and EC under 4.0 dS per metre.
5. Compare a patch. A yellow patch against a healthy patch in the same field shows whether soil is the cause.
6. Repeat every 3 to 5 years. The ICAR survey authors recommend this interval because status changes.

We did not find a university range for micronutrient levels in onion leaves, so there is no tissue-test table here. Until one is available from an Indian institute, the soil test plus symptoms is the reliable route.

DOGR recommends 10 kg zinc sulphate per hectare and 10 kg borax per hectare as basal doses in deficient areas, and 15 tonnes of farmyard manure per hectare plus a foliar micronutrient mixture at 45 and 60 days after transplanting where several nutrients are short. It says micronutrients raised bulb yield by 7 to 15 percent over control.

Source: ICAR-DOGR Onion Agropedia. The page writes the zinc source as ZnSO and omits the final digit, so it is read here as zinc sulphate. The foliar NPK line is a separate recommendation from the micronutrient mixture. A 19:19:19 water-soluble product supplies nitrogen, phosphorus and potassium, not zinc or boron, so it is not a micronutrient fix.

DOGR's monthly advisory for November 2026 gives standing late kharif onion a foliar spray of micronutrient mixture at 5 g per litre at 30, 45 and 60 days after transplanting (DOGR advisory). It lists no micronutrient spray for the onion seed crop. Check the current advisory on the DOGR website for the month you are in, because it changes with the season.

Both work, and the best trial results show them close. In a Rajasthan rabi trial, foliar zinc sulphate at 0.5 percent gave the highest growth and yield and was not significantly different from soil application of 25 kg per hectare. Soil application suits a known, field-wide shortage. Foliar spray suits a shortage seen in a standing crop.

Reading across, the Agra gain from zinc and boron was 1.77 t per hectare, about 5.8 percent by our arithmetic, a little below DOGR's 7 to 15 percent figure for micronutrients as a group, so results vary by field. In the Jobner trial the foliar spray matched the soil dose.

For the difference between a soluble spray and a granular basal, see water-soluble versus granular fertiliser and the water-soluble fertilizer buying guide.

Put sulphur, zinc and boron on as a basal dose at or before transplanting, because DOGR gives them as basal. Use foliar micronutrient sprays at 30, 45 and 60 days after transplanting when a shortage is seen or several nutrients are short. Correct a shortage as soon as it is confirmed.

The nitrogen and potassium splits sit alongside this calendar and are in the onion farming guide; the pre-transplant stage is in the nursery schedule.

Yes, mainly through sulphur and the overall fertilizer load. DOGR gives 50 kg S per hectare for long-day onion, against 15 or 30 kg for the others. DOGR says hill-grown long-day onion needs more fertilizer than short-day onion because of its longer duration and yield potential. Its micronutrient rates are given once, for deficient areas, without a split by season.

DOGR separates the crop into kharif at 25 to 30 t per hectare, late kharif and rabi at 40 to 50 t, and long-day onion in the hills at 100 t. Its nitrogen totals are 75, 110 and 180 kg per hectare respectively, with the phosphorus and potassium also stepped up for the long-day crop.

The seed crop is different again. DOGR's November advisory lists nitrogen for the onion seed crop at 30 kg per hectare at 30 and again at 45 days after planting, and lists no micronutrient spray. If you grow seed onion, take the seed-crop advice from your state institute or DOGR itself.

The common ones are applying without a soil test, correcting pH last instead of first, waiting for severe symptoms, and treating a micronutrient spray as a substitute for sulphur or NPK. Each costs money without a yield gain, and each is avoided by testing first, following the official rate and correcting pH early.

• Skipping the soil test. Boron is adequate in most Madhya Pradesh and Rajasthan soils and short in most of Maharashtra and Gujarat, so a recipe from another state can be wrong for yours.
• Ignoring pH. DOGR's range is 6.0 to 7.5; outside it, the nutrient may be present but not available.
• Waiting. DOGR says to correct deficiencies immediately, not at the next stage.
• Treating a 19:19:19 spray as a micronutrient. It carries nitrogen, phosphorus and potassium, not zinc or boron.
• Forgetting sulphur because it is not a micronutrient. It is the nutrient most often missing in the survey.
• Guessing from the leaf alone. Use the NIPHM symptom descriptions as a prompt to test, and confirm with the soil result.

If plants are pale and slow overall and you are not sure whether it is nutrition, the posts on nitrogen deficiency and why plants grow slowly help you rule out the other causes.

It helps but does not replace them where soils are short. DOGR pairs 15 t of farmyard manure per hectare with the foliar micronutrient mixture for multiple deficiencies, and an Agra trial found 10 t FYM added 3.35 t per hectare on top of 100 percent NPK. Manure raises organic carbon, which the survey links to zinc status.

The Agra trial also found that FYM with 100 percent NPK raised the soil's available N, P, K, S, Zn and B after harvest compared with NPK alone, while the control plots had the lowest available nutrients.

So the practical combination is manure for the base, a soil test to find the gaps, and a targeted sulphur, zinc or boron dose for the confirmed gap. Where no soil test is available, DOGR's 15 t FYM plus foliar mixture route is its own answer to a multi-nutrient problem.

Check sulphur first, correct any confirmed zinc or boron shortage, and hold soil pH at 6.0 to 7.5, as DOGR advises. In the trials cited here, sulphur and zinc gave measurable bulb yield gains. Nutrition alone will not fix variety, spacing or irrigation.

The evidence in this post: DOGR's 7 to 15 percent micronutrient yield gain, the Rajgurunagar sulphur trial's 39.1 t per hectare at 75 kg S, and the Mandsaur result that sulphur with nitrogen raised bulb diameter, yield and pyruvic acid. None of this is a promise for your field; it is a reason to look at sulphur and zinc before adding more NPK.

For the place of potassium and the full NPK schedule, which also drives bulb size, use the onion farming guide. The onion crop products collection groups our pest, disease and nutrition lines for onion in one place; its page does not describe an onion dose for any item, so use it to browse and not to choose a rate.

Ask for the soil report, not the crop name, before recommending a nutrient. Boron is short in most Maharashtra soils but few Madhya Pradesh soils. Quote ICAR-DOGR or your state package for the dose, and keep the survey table to explain why a farmer's neighbour's recipe may not suit his soil.

• Match the nutrient to the report. Sulphur, zinc and boron first; iron in the alkaline soils of the western states, where the survey found it higher.
• Explain pH. If the soil is outside 6.0 to 7.5, advice on pH comes before advice on a micronutrient.
• Know the pack. A product page that lists "all crops" or "vegetables" does not guarantee an onion response; use the pack label and the official dose.
• Keep records. The ICAR authors recommend re-testing every 3 to 5 years.
• Send serious cases to the KVK. If symptoms do not fit any picture, an extension officer should look at the field.

For stocking decisions, our soil health card guide helps a dealer read the card a farmer brings.

Conclusion

Micronutrient management in onion starts with the soil report and ends with a small number of targeted actions. Check sulphur first, then zinc and boron, and keep pH between 6.0 and 7.5 so the nutrients are usable. Follow the ICAR-DOGR rates for deficient fields, use a foliar mixture when several nutrients are short or a shortage shows in the crop, and correct it straight away. Do not copy a recipe from another state, and re-test every few seasons.