Updated: 3 October 2026
Zinc sulphate is the usual cure for zinc deficiency in rice, the problem called khaira in north India. It is sold in two grades: 21% zinc (heptahydrate) and 33% zinc (monohydrate). A company label for the 33% grade recommends 5 kg per acre for paddy and wheat at sowing or transplanting, or 15 days later; trial doses in rice range from 12.5 kg to 25 kg per hectare, and up to 40 kg in sodic soil.
No government price is fixed for zinc sulphate. Ask the dealer for the printed MRP and the grade.
Grades and zinc per bag
PAU researchers describe zinc sulphate heptahydrate (ZnSO4.7H2O) as 21% zinc and the monohydrate (ZnSO4.H2O) as 33% zinc. The grade decides how much zinc a kilo carries.
| Grade | Zinc in 10 kg | Zinc in 25 kg | Quantity for 5 kg of zinc |
|---|---|---|---|
| 21% heptahydrate | 2.1 kg | 5.25 kg | 23.8 kg (5 / 0.21) |
| 33% monohydrate | 3.3 kg | 8.25 kg | 15.2 kg (5 / 0.33) |
The two grades are not interchangeable kilo for kilo. A 33% bag has 1.57 times the zinc of a 21% bag (33 / 21), so it should cost about 1.57 times as much per kg for the same price of zinc.
Khaira: how zinc deficiency looks in rice
The IRRI Rice Knowledge Bank lists these signs, which appear two to four weeks after transplanting:
- dusty brown spots on the upper leaves of stunted plants
- uneven growth, with patches of poorly established hills
- chlorotic (pale) midribs, mostly near the base of younger leaves, and sometimes a white line along the midrib
- brown blotches and streaks on lower leaves that join up; in severe cases tillering decreases or stops and maturity is delayed
Mild cases can recover after 4 to 6 weeks, but maturity is delayed and yield is lower. The same symptoms can come from iron deficiency, iron toxicity, grassy stunt virus or tungro virus, so a soil and plant test is the way to confirm. IRRI lists alkaline or sodic soil, flooding, a lot of phosphate, heavy organic manure and sandy soil among the causes. PAU reported that 54.5% of intensively cultivated soils in Punjab are zinc deficient, with a soil test value (DTPA-Zn) below 0.6 mg per kg marking deficient fields in its trials. A Soil Health Card test shows the zinc level of the field.
Doses found in research and company advice
| Crop and source | Dose | Result or note |
|---|---|---|
| Rice, SPIC (company, 33% grade) | 5 kg per acre at planting or 15 days later | Manufacturer recommendation, not a trial |
| Rice, ANGRAU Tirupati, 12 farmer fields, 2019-21 | 25 kg zinc sulphate per hectare, basal | 6,339 kg per hectare against 5,790 without zinc in 2019-20; net return ₹94,577 against ₹85,948 per hectare |
| Rice, ANGRAU Anakapalle, 2012 and 2013 | 12.5 kg per hectare to soil plus two leaf sprays at 21 and 60 days after transplanting | Highest yield, 5.41 and 5.26 tonnes per hectare; spray strength not given in the abstract |
| Rice in sodic soil, ICAR journal study | 40 kg per hectare standard; 20 kg with farmyard manure or pressmud | 20 kg mixed with organic matter matched 40 kg alone |
| Wheat, SPIC (company, 33% grade) | 5 kg per acre at sowing or 15 days later | Manufacturer recommendation, not a trial |
| Maize | No dose given here | No ICAR or state university maize dose is cited; ask the KVK after a soil test |
The grade of zinc sulphate used in the ANGRAU and ICAR trials is not stated in the abstracts, so the zinc in 25 kg depends on whether it was 21% (5.25 kg zinc) or 33% (8.25 kg). The leaf-spray strength is not given here; ask the KVK before spraying.
Why not mix it with phosphatic fertiliser
- IRRI lists the formation of zinc phosphates after large phosphate applications as a cause of zinc deficiency. Zinc locked up that way is not available to the crop.
- There is no confirmed rule for mixing zinc sulphate with DAP in the field. Applying it separately avoids the question.
- Factory-made zinc-fortified DAP and SSP are a different product. In PAU trials on five farmer fields in Punjab, zinc-fortified DAP raised wheat grain yield by 4.1 to 5.8% over nitrogen and potash alone, and zinc-fortified DAP or SSP plus a zinc spray raised rice grain yield by about 14.4 to 16.5%. PIB notes that zinc-fortified P&K grades get an extra subsidy of ₹500 per tonne.
Spotting adulteration
- A company specification for 33% zinc sulphate (SPIC) requires at least 33% zinc, at least 15% sulphate sulphur, at most 1% water-insoluble matter, at most 1% iron, a 5% solution with pH not below 4, and strict limits on cadmium (0.0025%) and arsenic (0.01%). Only a laboratory can check these.
- No reliable home test from an official source is known, so none is given here. A sealed bag that states the grade, manufacturer and batch, with a bill, is the minimum. Doubt a price that does not follow the grade ratio above.
- For a suspect bag, keep it sealed with the bill and report it to the district agriculture office. See fertilizer guide and fertilizer prices for other inputs.
Sources
- Saini, Dheri and Singh, Indian Journal of Agricultural Sciences 91(7), 2021 (PAU, zinc in rice-wheat)
- SPIC Zinc Sulphate 33% product page (company specification and dose)
- IRRI Rice Knowledge Bank, zinc deficiency
- Influence of zinc application on yield, economics and soil zinc status in paddy (ANGRAU, Tirupati)
- Oryza (ICAR journal), zinc enrichment in rice grain (ANGRAU, Anakapalle)
- Indian Journal of Agricultural Sciences, rice and zinc sulphate in sodic soil
- PIB backgrounder on NBS rates, 5 January 2026