Zinc and Micronutrient Seed Coating in Wheat: What Indian Trials Actually Show

Executive Summary

Zinc is the micronutrient an Indian wheat crop is most likely to run short of, and the seed is the smallest place anyone has tried to put it. Nearly half of Indian soils are poor in available zinc, and soil and foliar zinc are the established answers. The seed route is newer, works through the seedling rather than the crop, and the Indian evidence for it is real but narrow.

The clearest Indian field numbers come from cotton: at Dharwad in kharif 2017–18, one gram of nano zinc oxide per kilogram of seed in a polymer film out-yielded chelated zinc sulphate at four grams per kilogram by 23.08 per cent. In wheat the sharpest Indian result is a laboratory one from Pantnagar, where the treatment that lifted seedling length and dry weight by about a third at 50 ppm reversed at 100 ppm. The one seed-route result with Indian field locations, zinc-biofortified seed, shows soil zinc winning at all six Indian sites against four for the seed itself.

Why Zinc Is the First Micronutrient Question in Indian Wheat

A 2013 review from the Division of Agronomy at the Indian Agricultural Research Institute, New Delhi, puts nearly half of Indian soils poor in available zinc. Its state table of DTPA-extractable zinc deficiency runs from 8 per cent of samples in Puducherry to 78 per cent in Maharashtra, with 24.6 per cent in Punjab, 26.4 in Haryana, 38.9 in Uttar Pradesh and 65.3 in Bihar and Jharkhand. An analysis of 0.233 million soil samples, cited in the Dharwad study below, put the national figure at 47 per cent. The same review fixes the critical limit for wheat on Indian alluvial soils at 0.40 to 0.80 mg/kg of DTPA-extractable zinc, and reports an average wheat response to zinc fertilisation of 380 kg of grain per hectare.

Two properties of zinc make the seed a logical delivery point. Zinc is relatively immobile in the plant, so deficiency appears in young tissue that cannot be resupplied from older leaves. And until a wheat seedling’s roots are exploring soil, it lives largely on the zinc inherited in the seed itself — the relationship established by Rengel and Graham on zinc-deficient soil.

Four Different Things Called “Zinc Seed Coating”

Most confusion about zinc seed treatment comes from lumping four distinct techniques under one label. They differ in what is applied and in how strong the Indian evidence is.

The first three are things a seed company does to a seed lot; the fourth is a property of the seed lot, and it is the one with Indian field locations.

The Dose Window: A Wheat Germination Study from Pantnagar

The most useful Indian wheat data here is not a field trial. Published in 2020 in the International Journal of Current Microbiology and Applied Sciences, it comes from G.B. Pant University of Agriculture and Technology, Pantnagar, with co-authors from S.V.P. University of Agriculture and Technology, Meerut. The team synthesised zinc oxide nanoparticles from Catharanthus roseus leaf extract, characterised them at an average 385 nm, and treated seed of the wheat Triticum aestivum variety WH 1105 at 20, 50 and 100 ppm.

The result splits in two. Germination percentage, speed of germination and mean germination time did not differ significantly at any concentration. Everything describing the seedling did move: at 50 ppm, root length rose from 11.57 to 14.60 cm, shoot length from 8.20 to 11.63 cm, seedling length from 19.77 to 26.23 cm and seedling dry weight from 16.67 to 22.43 mg — gains of 26.2, 41.9, 32.7 and 34.6 per cent respectively.

At 100 ppm all of those measures fell back, which the authors read as nanoparticle toxicity at the higher concentration. A zinc seed treatment in wheat is therefore not a germination treatment, and the margin between the concentration that helps a seedling and the one that harms it is small.

Field Evidence from India: Nano-Zinc Seed Treatment in Cotton at Dharwad

The strongest Indian field evidence for a zinc seed dressing comes from cotton. The trial ran at the Main Agricultural Research Station of the University of Agricultural Sciences, Dharwad, Karnataka, in kharif 2017–18, on the Bt cotton Gossypium hirsutum hybrid Superb SP7157. Three seed treatments were compared: chelated zinc sulphate at 4 g per kg of seed in 8 ml of polymer, nano zinc oxide at 1 g per kg of seed in the same polymer volume, and priming in a 1,000 ppm nano-zinc solution for eight hours.

Nano zinc oxide gave the highest seed cotton yield at 2842 kg/ha, against 2478 kg/ha for priming and 2309 kg/ha for chelated zinc sulphate — 23.08 per cent above the chelated salt. Alone it returned gross returns of ₹1,37,818 per hectare, net returns of ₹73,568 and a benefit–cost ratio of 2.1; with a foliar spray of nano zinc oxide at 1,000 ppm, yield rose to 3221 kg/ha and net returns to ₹88,128.

Two things carry over to wheat and one does not. The mechanism carries over: a small mass of zinc fixed in a polymer film at sowing can change the plant, and the carrier matters as much as the zinc source, which is why the 8 ml of polymer per kilogram is stated as deliberately as the zinc rate. The crop does not.

Zinc-Biofortified Seed: the One Seed-Route Result with Indian Locations

If the question is what higher zinc inside the seed does to an Indian wheat crop, the reference study is a 31-location, two-year, six-country field trial published in the Journal of Plant Nutrition and Soil Science in 2019, with co-authors including scientists from Punjab Agricultural University, Ludhiana. Wheat experiments ran in China, India, Pakistan and Zambia; rice in China, India and Thailand.

The design separates the routes cleanly: low-zinc seed with no soil zinc as the control; low-zinc seed plus soil zinc fertilisation; and zinc-biofortified seed from a maternal crop that had received foliar zinc, with no soil zinc. The biofortified seed carried no coating at all.

Across all countries and both years, zinc-biofortified wheat seed raised plant population by 26.8 per cent and grain yield by 5.37 per cent against the control. In India, soil zinc fertilisation raised wheat grain yield at all six Indian locations, while zinc-biofortified seed raised it at four. Rice showed the same ranking, with 8.2 per cent more paddy yield from soil zinc against 5.3 per cent from biofortified seed.

A larger zinc reserve inside the seed helps establishment — the plant population effect is the largest number in this literature — but where soil zinc was applied in the same trial it did more for wheat yield than the seed’s own reserve.

Table: What the Indian and India-Linked Trials Actually Measured

The last row is the benchmark. The strongest recent Indian wheat number here does not involve the seed at all.

What Soil and Foliar Zinc Still Do Better in India

Soil application on zero-till wheat, Amritsar

A two-season experiment on zero-tilled wheat at Khalsa College, Amritsar, tested soil applications of 12.5, 25, 37.5 and 50 kg/ha of zinc sulphate heptahydrate, alone and with 0.5 per cent foliar zinc sprays at heading initiation, at full heading, or both, against a no-zinc control, in rabi 2018–19 and 2019–20. The best treatment — 50 kg/ha of soil zinc with two foliar sprays — gave about 25 per cent more grain yield than the control, grain zinc of 41.77 ppm against 31.20 ppm, and the highest net returns.

Foliar zinc at heading, Punjab and Rajasthan

Foliar zinc has a consistent Indian record of its own. At Chunni Kalan in Fatehgarh Sahib district, Punjab, in rabi 2016–17, the top of eight treatments produced 5.30 t/ha of grain and 6.43 t/ha of straw, and what distinguished it was a 0.2 per cent zinc sulphate foliar spray at heading. A front-line demonstration in Sri Ganganagar district, Rajasthan, in rabi 2022–23 found that 120 kg N and 40 kg P per hectare with 6 kg/ha of zinc sulphate sprayed at 40 days after sowing gave higher grain and straw yield, net realisation and fertiliser-use efficiency than the prevailing farmers’ practice.

Both are the benchmark the seed route must be measured against, and in Indian wheat that benchmark is high. Both also depend on the grower turning up at a particular growth stage; the seed coat’s appeal is that the input arrives already on the seed.

Putting a Zinc Coat on Seed That Is Already Dressed

An Indian wheat seed lot is rarely bare. It is normally dressed before sale or sowing, usually with a fungicide and sometimes with an insecticide too. Any film carrying zinc has to go on over, or under, that dressing without interfering with it, which makes compatibility the practical centre of the question.

The closest Indian evidence that a polymer film over an existing dressing holds up in wheat comes from CSKHPKV Palampur in Himachal Pradesh. In a field trial sown in December 2018 on carry-over seed of the rabi 2017–18 crop, using wheat variety HPW-155, the best of ten treatments was a polymer coating at 3 ml per kg over a thiram and carboxin dressing at 2 g per kg: 52.12 q/ha against 45.45 q/ha for untreated seed, a 14.7 per cent gain, with tillers per plant of 4.80 against 2.40 and a 1,000-grain weight of 51.37 g against 47.00 g.

Yaduka Agrotech Limited holds CIB&RC Section 9(4) registrations for carboxin 17.5% + thiram 17.5% FF, registration CIR-367394/2026-Carboxin + Thiram (FF) (472)-140, for loose smut of wheat at 25–30 ml per 10 kg of seed with a 100 ml dilution, and for tebuconazole 5.4% w/w FS, registration CIR-367398/2026-Tebuconazole (FS) (472)-212, whose certificate names wheat, at 3.0 ml per 10 kg of seed for loose smut and flag smut. Those are statements about what we are licensed to sell, not evidence that the products perform; our thiram 40% FS registration covers maize, not wheat. Seed Primer, the multilayer biopolymer coating built around Trichoderma harzianum Th4d, is the same class of object as the Palampur film — a carrier that holds an active against the seed — and a zinc salt or zinc oxide particle would sit in that same film.

The Arithmetic of a Few Hundred Grams

The Dharwad trial applied 4 g of chelated zinc sulphate per kilogram of seed in 8 ml of polymer. Applied at the 100 kg/ha wheat seed rate common in north-west India, that works out to 400 g of product per hectare. Since zinc sulphate heptahydrate is roughly 22.7 per cent zinc by mass, it carries about 0.09 kg of actual zinc per hectare. Soil application at 25 kg/ha of the same salt carries roughly 5.7 kg of zinc, and the heaviest Amritsar treatment, 50 kg/ha, about 11 kg.

That settles whether a zinc seed coat replaces soil zinc: on the quantities involved it cannot, and the Indian field data do not suggest it does. What the seed route offers is placement — a very small quantity of zinc held millimetres from the embryo at germination, applied at a dressing line the seed company already runs, with no extra field operation.

Where the Indian Evidence Is Still Thin

Four gaps are worth naming, because each is where a supplier’s claim tends to run ahead of the record.

• The wheat evidence is thin where the others are thick. Soil and foliar zinc in wheat, and the zinc seed dressing in cotton at Dharwad, both rest on multi-season or multi-location Indian field data. The published Indian work on zinc applied to wheat seed is largely at seedling and pot scale.
• Source and dose are not standardised. The work reviewed here used green-synthesised zinc oxide nanoparticles, chelated zinc sulphate in a polymer film, plain zinc sulphate solutions and zinc-biofortified seed. These are not interchangeable.
• Pot numbers do not travel. A 2022 pot study on bread wheat reported a 63.1 per cent grain yield increase from priming with 0.5 M zinc sulphate — far above anything a field trial returns.
• Grain zinc is not the outcome to sell on. In the 31-location trial the effects of both soil zinc and high-zinc seed on grain zinc density were generally low, so the measurable differences sit in establishment and, modestly, in yield — well below the 25 per cent available from soil plus foliar zinc in a deficient zero-till wheat field.

None of this makes a zinc seed treatment a bad idea. It makes it an unfinished one, which is why the honest Indian position is what the IARI review and the Amritsar trial both imply: correct the deficiency in the soil, top it up on the leaf where the crop is heading, and treat the seed as an additional point of delivery rather than the correction itself.

Practical Guidance for Seed Companies and Growers

At the seed company

• Choose the zinc source before the rate. Nano zinc oxide at 1 g/kg and chelated zinc sulphate at 4 g/kg are not the same product at different strengths; at Dharwad the difference changed the yield ranking.
• Keep the applied mass small. A film that will not dry, or that bridges seed in the bag, is a storage problem waiting to happen.
• Fix the order of operations with your existing dresser: at Palampur the best result came from a polymer film over a thiram and carboxin dressing, not from either alone.
• Measure what moves. At Pantnagar, germination percentage did not budge at any zinc concentration; seedling length, seedling dry weight and vigour index did.

On the farm

• Soil test first. The critical limit for wheat on alluvial soils is 0.40–0.80 mg/kg of DTPA-extractable zinc; below that line the correction is soil zinc, optionally with foliar zinc at heading.
• Treat a zinc-coated seed as an addition, not a replacement: it carries a fraction of one per cent of the zinc a soil application carries.
• Judge treated seed on stand and seedling vigour, not on grain zinc claims Indian field trials have not consistently delivered.
• Ask for the dose per kilogram of seed, and for the zinc source; a per-hectare figure cannot be dosed reproducibly at the dressing line.

Conclusion

Zinc is the micronutrient that most limits an Indian wheat crop on the soils where it is short, and the one attracting most commercial interest in new delivery routes. The seed route deserves that interest: at Pantnagar a 50 ppm zinc oxide seed treatment lifted wheat seedling length by about a third, at Dharwad 1 g of nano zinc oxide per kilogram of seed out-yielded chelated zinc sulphate at 4 g/kg by more than 23 per cent, and across 31 locations in six countries higher-zinc wheat seed raised plant population by 26.8 per cent.

The ceiling is visible in the same literature. The wheat dose response turns down above about 50 ppm in the laboratory, so this is a narrow window, not a dial. The only seed-route result with Indian field locations shows soil zinc beating the seed’s own reserve at every Indian site. And the strongest recent Indian wheat number, from zero-till wheat at Amritsar, comes from soil and foliar zinc and not from the seed. The Indian record supports a zinc seed treatment as a low-cost, well-placed starter applied at the dressing line a seed company already runs. It does not yet support a zinc seed coat as the answer to a zinc-deficient wheat field.

References and Sources

1. Prasad, R., Shivay, Y. S. and Kumar, D. (2013). Zinc Fertilization of Cereals for Increased Production and Alleviation of Zinc Malnutrition in India. Agricultural Research 2(2): 111–118. Indian Agricultural Research Institute, New Delhi. doi:10.1007/s40003-013-0064-8
2. Meher, B. B., Sahu, S., Singhal, S., Joshi, M., Maan, P. and Gautam, S. (2020). Influence of Green Synthesized Zinc Oxide Nanoparticles on Seed Germination and Seedling Growth in Wheat (Triticum aestivum). International Journal of Current Microbiology and Applied Sciences 9(5): 258–270. G.B. Pant University of Agriculture and Technology, Pantnagar. doi:10.20546/ijcmas.2020.905.029
3. Pruthvi Raj, N. and Chandrashekara, C. P. (2019). Nano Zinc Seed Treatment and Foliar Application on Growth, Yield and Economics of Bt Cotton (Gossypium hirsutum L.). International Journal of Current Microbiology and Applied Sciences 8(8): 1624–1630. University of Agricultural Sciences, Dharwad. doi:10.20546/ijcmas.2019.808.192
4. Rashid, A., Ram, H., Zou, C., Rerkasem, B., Duarte, A. P., Simunji, S., Yazici, A., Guo, S., Rizwan, M., Bal, R. S., Wang, Z. and others (2019). Effect of zinc-biofortified seeds on grain yield of wheat, rice, and common bean grown in six countries. Journal of Plant Nutrition and Soil Science 182(5): 791–804. doi:10.1002/jpln.201800577
5. Thakur, A., Dhiman, K. C. and Kanwar, R. (2021). Effect of polymer and plant protectants based seed treatment on crop performance in wheat (Triticum aestivum L.). Journal of Cereal Research 13(Spl-1): 92–96. CSKHPKV, Palampur. doi:10.25174/2582-2675/2021/115272
6. Effect of zinc management on yield, nutrient content, and acquisition of zero-tilled wheat (Triticum aestivum). Indian Journal of Agronomy 69(3). Khalsa College, Amritsar, rabi 2018–19 and 2019–20. doi:10.59797/ija.v69i3.5520 and doi:10.59797/ija.v69i3.5590
7. Shalini, Ahamad, A., Singh, A. and Kumar, A. (2020). Effect of zinc fortification on growth, yield and economics of wheat (Triticum aestivum L.) under irrigated condition of Punjab. International Journal of Chemical Studies 8(3): 266–270. Dolphin (PG) College of Science and Agriculture, Chunni Kalan, Fatehgarh Sahib, rabi 2016–17. doi:10.22271/chemi.2020.v8.i3d.9239
8. Sharma, B., Singh, B., Kumari, R., Kumari, P., Ali, S. and Chawla, S. (2025). Enhancing Wheat Productivity, Profitability, Nutrient Use Efficiency, and Carbon Yield through Foliar Application of Zinc Sulphate in Western India. Journal of Extension Systems 41(1): 29–33. Sri Ganganagar, Rajasthan, rabi 2022–23. doi:10.48165/jes.2025.41.1.5
9. Nauman Ali, Farooq, M., Ahmad Hassan, M., Arshad, M. S., Saleem, M. K. and Faran, M. (2018). Micronutrient seed priming improves stand establishment, grain yield and biofortification of bread wheat. Crop and Pasture Science. University of Agriculture, Faisalabad. Cited for comparison; non-Indian. doi:10.1071/CP18042
10. Rehman, A., Farooq, M., Ullah, A., Nawaz, A., ud Din, M. M. and Shahzad, B. (2022). Seed priming with zinc sulfate and zinc chloride affects physio-biochemical traits, grain yield and biofortification of bread wheat. Crop and Pasture Science. Pot study, cited for comparison; non-Indian. doi:10.1071/CP21194
11. Singh, S., Kaur, J., Ram, H., Singh, J. and Kaur, S. (2023). Agronomic bio-fortification of wheat (Triticum aestivum L.) to alleviate zinc deficiency in human being. Reviews in Environmental Science and Bio/Technology. Punjab Agricultural University, Ludhiana. doi:10.1007/s11157-023-09653-4

CIB&RC registration details for Yaduka Agrotech Limited products are quoted from the certificates and labels on file with the company and describe the scope of registration only. No efficacy claim is made from a registration.