Ammonium sulfate vs urea: yield and cost comparison

Choosing between ammonium sulfate (AS) and urea involves a trade-off between nutrient content, cost, soil impact, and application risks.

Cost Comparison

• Urea (46-0-0): Is almost always cheaper per pound/kg of nitrogen. Its high nitrogen analysis (46%) means you buy, transport, and spread less product to get the same amount of N compared to AS.
• Ammonium Sulfate (21-0-0-24S): Is more expensive per pound of nitrogen. However, its price includes 24% sulfur, which has significant value if your soil is sulfur-deficient. If you need to apply sulfur anyway, AS can be more cost-effective.

Yield and Performance Comparison

• Sulfur Deficiency: In sulfur-deficient soils, ammonium sulfate will often produce a higher yield than urea because it supplies both critical nutrients.
• Volatilization Risk: Urea is highly prone to volatilization. If surface-applied without being incorporated by tillage or rainfall, a large portion of its nitrogen can be lost to the atmosphere as ammonia gas. Ammonium sulfate has a much lower volatilization risk. This means in no-till or dry-weather surface applications, AS often provides a better yield because more nitrogen actually reaches the plant.
• Soil pH: Ammonium sulfate has a much stronger acidifying effect on soil than urea. In alkaline soils (high pH), this acidification can improve nutrient availability (like iron and manganese) and boost yield. On acidic soils (low pH), this same effect can harm yields unless corrected with lime.
• Salt Index: Ammonium sulfate has a high salt index, meaning it has a greater potential to cause seed or seedling burn if placed too close to the seed. Urea has a lower salt index.

Urea is cheaper for bulk nitrogen, but ammonium sulfate often provides better performance and yield in specific situations: 

1) when sulfur is needed, 

2) on alkaline soils, or 

3) when fertilizer is surface-applied without incorporation.