ASN vs. Ammonium Sulfate: Which One Is the Better Partner for Your Fields?
If you're currently using ammonium sulfate, or considering a nitrogen sulfur Compound Fertilizer for your customers, this article is worth a few minutes of your time. Because ASN and ammonium sulfate—despite both delivering nitrogen plus sulfur—are far more different than you might think.
- Know the Basics: A Quick Profile of the Two Fertilizers
Ammonium sulfate (SOA) is a classic fertilizer that supplies both nitrogen and sulfur. The common grade contains about 21% N and 24% S (as sulfate), both directly available to plants. One key agronomic advantage: when surface applied on acidic or neutral soils, SOA essentially suffers no ammonia volatilization loss, making it a better choice than urea under certain soil conditions.
ASN (Ammonium Sulfate Nitrate) builds on ammonium sulfate by incorporating the nitrate ammonium system, creating a next generation product. A typical ASN specification is 26% total nitrogen (split into approx. 7.5% nitrate N and 18.5% ammonium N) plus 13% sulfur. Unlike ammonium sulfate, which supplies only ammonium N, ASN perfectly combines both ammonium and nitrate nitrogen, bringing the advantages of both forms into one product.
- Efficiency: Where the Pathways Diverge
Crop uptake efficiency – ASN's dual N synergy delivers clear benefits. In maize, using an ammonium sulfate fertilizer with a nitrification inhibitor (i.e., an ASN type product) increased nitrogen use efficiency by 6.17 percentage points and agronomic N efficiency by 5.10 kg/kg compared to conventional ammonium sulfate. In potatoes, ASN with an enhancer produced 34% higher fresh tuber yield per unit of applied N than ordinary SOA, and 50 75% higher than a single application. The reason for this efficiency jump is simple: the nitrate fraction in ASN is taken up immediately, while ammonium N is retained longer and released steadily – a synergistic effect that pure ammonium N cannot match.
Leaching and residual N – The difference is equally clear. Compared to urea and ordinary SOA, the ASN treatment with a nitrification inhibitor significantly reduced the downward movement of total N, ammonium N and nitrate N into deeper soil layers, leaving more residual N accumulated in the 0 10 cm topsoil. This means that ASN not only cuts nutrient losses but also leaves a better nitrogen bank for the next crop – something SOA struggles to achieve.
- Soil Health: Can You Use It Long Term? The Answers Are Opposites
For any grower who values sustainable soil productivity, this is the most important dimension.
Ammonium sulfate is a physiologically acidic fertilizer. When crops absorb ammonium ions, they release large amounts of hydrogen ions around the roots. Long term application of SOA progressively lowers soil pH. The literature clearly states that one of the long term negative effects of ammonium sulfate is strong soil acidification, often requiring increasing amounts of lime to neutralise. Field studies have shown that after SOA application, soil exchangeable base cations drop sharply, pH declines, and these adverse changes extend into deeper soil layers, making later remediation difficult.
ASN is fundamentally different. ASN is a dual salt composite whose crystal lattice consists of alternating ammonium, nitrate and sulfate ions, avoiding the strongly acidic residue of purely ammonium based fertilizers. Product specifications describe ASN as a near neutral pH fertilizer, suitable for a wide range of soils and crops. When it comes to protecting long term soil productivity, ASN is a far safer bet than ammonium sulfate.
- Real World Data: Which One Performs Better in the Field?
Numbers and facts are the best advocates.
Maize trial – Using a nitrification inhibited ammonium sulfate fertilizer (i.e., an ASN type product) increased maize yield by 11.07% and N use efficiency by 6.17 percentage points compared to conventional ammonium sulfate alone.
Spring wheat & canola – On neutral, sulfur deficient soils, both fused ASN and granular ASN produced cumulative yields comparable to urea, while fused ASN performed best on canola seed yield. Both outperformed MAP enriched with elemental sulfur.
Potatoes in Brazilian sandy soils – Split applications of ASN with the DMPP nitrification inhibitor increased fresh tuber yield by 15% while allowing a 25% reduction in total N rate compared to conventional practices.
- References
[1] Effects of ammonium sulfate synergistic measures on yield, nitrogen uptake and utilization of maize (CNKI), key findings: The ASN type treatment increased maize yield by 11.07% and NUE by 6.17 percentage points vs. plain SOA.
[2] Split application of stabilized Ammonium Nitrate improved potato yield and NUE with reduced application rate in tropical sandy soils. Field Crops Research, 2020.Key findings: Split ASN + DMPP increased fresh tuber yield by 15% and yield per unit N by 34%.
[3] Evaluation of Fused Ammonium Sulfate Nitrate Fertilizer for Crop Production. Soil Science, 178(2):79-86, 2013.Key findings: Fused and granular ASN performed similarly to urea on ryegrass and canola; both outperformed MAP+elemental S.
[4] Oil Coated Ammonium Sulfate Improves Maize Nutrient Uptake and Regulates N Leaching Rates in Sandy Soil (Agronomy, 2024) Key findings: ASN with a nitrification inhibitor significantly reduced N leaching and kept more residual N in the topsoil.
[5] Comparison of Ammonium Sulfate With Other Nitrogen and Sulfur Fertilizers (FAO AGRIS / Chien et al., 2011) Key findings: SOA has agronomic and environmental benefits, but its high acidification potential requires more lime input.
For international buyers and growers, choosing between ammonium sulfate and ASN is fundamentally a trade off between short term cost and long term value.
- If you need only basic N+S supply and your budget is tight, ammonium sulfate is a workable option.
- But if you value higher nitrogen efficiency, soil health protection, and better crop yields, ASN is clearly the smarter upgrade.
For large scale farms that need to sustain soil productivity, and for growers of high value cash crops who pursue the best return on inputs, the extra benefits of ASN will likely far exceed its slightly higher upfront price.