For decades, urea has been the default nitrogen fertiliser for Indian farmers. Urea is cheap, subsidised, and 46% nitrogen by weight. But ammonium sulfate is quietly catching up. Sulfur deficiency now affects an estimated 40% of Indian soils. Alkaline soils across the Indo-Gangetic plain are losing more urea-N to volatilisation each year, and the Nutrient-Based Subsidy (NBS) scheme has made ammonium sulfate (AMS) more accessible.
Urea vs Ammonium Sulfate: Core Differences
Urea (46-0-0) delivers the highest nitrogen concentration of any solid fertiliser at the lowest cost per kilogram of N, but loses 20–40% of its nitrogen to volatilisation when surface-applied without incorporation. Ammonium sulphate (21-0-0-24S) supplies less nitrogen per bag but adds 24% sulfur, resists volatilisation, and acidifies alkaline soils, making it the smarter pick for sulfur-deficient or high-pH conditions.
What Is Urea?
Urea is the organic compound CO(NH₂)₂, the same nitrogen-rich molecule mammals excrete in urine. As a fertiliser, it is manufactured industrially from ammonia, given the availability of Middle Eastern exports.
How urea behaves in soil
Once applied, urea undergoes hydrolysis by the soil enzyme urease, first forming ammonium carbonate, then ammonium (NH₄⁺), and finally, through nitrification, nitrate (NO₃⁻), which plants absorb. This conversion takes 2 to 10 days, depending on soil moisture, temperature, and microbial activity.
Why urea dominates Indian agriculture
Urea accounts for over 80% of India's nitrogen fertiliser consumption for three reasons:
- Highest nitrogen density of any solid, which lowers transport and handling costs per kg of N delivered
- Heavy government subsidy that keeps the retail price well below the production cost
- Universal crop suitability - works for cereals, sugarcane, fruits, vegetables, and most field crops
What Is Ammonium Sulphate?
Ammonium sulfate (AMS or AS), with the formula (NH₄)₂SO₄, is an inorganic crystalline or granular fertiliser supplying 21% nitrogen and 24% sulfur. Much of the global supply is produced as a co-product of caprolactam manufacturing, with the remainder produced by direct synthesis using ammonia and sulfuric acid.
How ammonium sulfate behaves in soil
Unlike urea, AMS does not need to be hydrolysed. Its nitrogen is already in the ammonium (NH₄⁺) form that plants and soil microbes can use immediately. The sulfate ion (SO₄²⁻) is also directly available to plants. As ammonium nitrifies to nitrate, hydrogen ions are released, which is what gives AMS its strong acidifying effect on soil.
Why is ammonium sulfate gaining popularity in India?
Four trends are driving AMS uptake.
- The first is widespread sulfur deficiency. Indian Institute of Soil Science surveys have flagged sulfur as a deficient or marginal nutrient across roughly 40% of cultivated land, particularly in rainfed and oilseed-growing belts.
volatilisation - The second is alkaline soil management. Large parts of UP, Punjab, Haryana, Rajasthan, and Gujarat have soil pH above 7.5, where urea volatilisation is highest, and micronutrient availability is lowest. AMS solves both problems.
- The third is NBS inclusion and improved supply. Inclusion under the Nutrient-Based Subsidy regime and steady caprolactam by-product output have made AMS more available and price-competitive on a per-bag basis.
- The fourth is supply-chain resilience. Repeated urea import shocks, including Russia-Ukraine price spikes, China's export restrictions, and Red Sea shipping disruptions, have prompted both policymakers and progressive farmers to think about diversifying nitrogen sources. AMS sits in a different, more dispersed global supply chain than urea, and we will return to this further down.
Why is Ammonium Sulphate a good alternative to Urea?
The economic benefits
Urea, priced at ₹50–60 per kg, delivers 46% nitrogen. But India’s soils absorb only 20–25% of that nitrogen. The rest is lost to volatilisation, leaching, and runoff. In practical terms, a ₹5,000–6,000 investment in 100 kg of urea delivers barely 10–12 kg of crop-available nitrogen, and it takes 15–20 days to convert from urea-N to the ammoniacal form that roots can actually use.
Ammonium sulfate, by contrast, is available at approximately ₹20 per kg. It supplies ammoniacal nitrogen directly, immediately plant-available, with no conversion lag. Its use efficiency ranges from 70–90%, compared to urea’s 20–25%. Additionally, it delivers 24% sulfur alongside 21% nitrogen, further improving overall Nutrient Use Efficiency (NUE) in a single application.
The policy arithmetic is equally striking. To deliver 10–15 kg of usable nitrogen to a farmer’s field, the government currently subsidises roughly ₹5,000–6,000 worth of urea. The same nutritional outcome can be achieved with 50 kg of ammonium sulfate at a cost of ₹1,250–1,500, while simultaneously addressing sulfur deficiency and improving soil health.
This is not an incremental improvement. It is a fundamental rethinking of nitrogen delivery in Indian agriculture.
Geopolitics
The nitrogen supply chain carries a structural vulnerability that geopolitics is now exposing in real time. The Middle East accounts for nearly a third of all globally traded urea, and nearly 49% of global urea exports. The 2026 Iran conflict has disrupted passage through the Strait of Hormuz for ammonia and urea shipments, creating price shocks that Indian procurement agencies are now managing under considerable pressure. Baltic FOB urea averaged $375/t in 2025, climbed to $418 by February 2026, and surged to $563–586/t by mid-March, a 40% increase in weeks. Ammonium sulfate operates in a fundamentally different supply paradigm. It is predominantly a by-product, generated as a co-product of caprolactam (nylon) synthesis, coke oven gas purification, and flue gas desulfurization in power plants. Because it emerges from existing industrial waste streams, its production cost is structurally low and not exposed to the same geopolitical supply shocks as synthetic nitrogen.
India, critically, has the manufacturing infrastructure to produce ammonium sulfate domestically through companies such as Grasim Industries, Reliance Industries, and GSFC, all of which generate ammonium sulfate as a by-product of their nylon and chemical operations. Unlike urea, for which India remains dependent on global gas markets and on the availability of Middle Eastern exports, ammonium sulfate offers a genuine pathway to fertiliser self-reliance. This is a food security argument, not just an agronomy one.
When to choose which?- A Decision Framework
The choice is not "urea or AMS forever." It is "which N source for this field, this crop, this season."
Choose urea when your soil pH sits between 6.0 and 7.2, your soil test shows adequate sulfur (above 15 ppm available S), you can incorporate within 24 hours or irrigate or expect rainfall, you are growing a heavy N-demanding cereal where cost per kg N matters most, and budget is the binding constraint.
Choose ammonium sulfate when your soil pH is above 7.5 (alkaline or calcareous), your soil test shows sulfur below 10 to 12 ppm, you are growing an oilseed, pulse, allium (onion or garlic), brassica, or tea, you cannot incorporate or irrigate immediately after application, and long-term soil acidification is acceptable or desired.
Use both, either as a split application or a blend, when your crop needs both heavy N and meaningful S (sugarcane and maize on S-deficient soil are classic cases), or when you want to reduce urea volatilisation losses without giving up its cost advantage. A 3:1 or 4:1 urea-to-AMS blend often delivers the best balance of cost, N density, and sulfur supply.
At Scimplify, we are actively building amsul-enriched speciality fertiliser and biostimulant combinations that integrate sulphur nutrition with humates, biologicals, and crop-specific nutrient programmes, helping Indian farmers make this transition with maximum agronomic impact.
The shift from urea to ammonium sulphate is not a disruption to Indian agriculture. It may be one of the most logical and overdue corrections it has ever seen.