What Are the Differences Between Urea and Ammonium Sulfate? (Applicable Comparison)

Choosing between ammonium sulfate and urea is not just a matter of comparing nitrogen percentages. Both fertilizers supply nitrogen, but they differ in sulfur content, nitrogen concentration, soil effects, and the risk of nitrogen loss after application. The right choice depends on your crop’s nutrient requirements, soil conditions, application method, and fertilizer budget. Urea contains about 46% nitrogen, making it a concentrated nitrogen source. Standard ammonium sulfate fertilizer contains approximately 21% nitrogen and 24% sulfur, so it can supply two essential nutrients in one product. However, neither fertilizer is suitable for every situation.

In this guide, we compare ammonium sulfate vs urea to help farmers and agricultural buyers understand their differences, evaluate their benefits, and choose the right fertilizer for their crops and soils. Earlier, we compared ammonium sulfate and ammonium nitrate. In this article, we are going to compare ammonium sulfate and urea.

Ammonium Sulfate vs Urea at a Glance

Feature	Ammonium Sulfate	Urea
Typical nitrogen content	21%	46%
Sulfur content	About 24% in standard fertilizer grade	None
Nitrogen form at application	Ammonium	Urea, which converts to ammonium in soil
Main advantage	Supplies nitrogen and sulfur	Delivers more nitrogen per kilogram
Surface application	Generally lower ammonia-volatilization risk than urea	Greater volatilization risk if left on the surface under favorable conditions
Soil pH effect	Acidifying over time	Also acidifying over time
Best suited to	Crops requiring both nitrogen and sulfur	Crops primarily requiring nitrogen
Common physical forms	Crystalline and granular	Prilled and granular

What Is the Difference Between Urea and Ammonium Sulfate?

The main difference between urea and ammonium sulfate is their nutrient composition and how their nitrogen behaves after application.

What Is Urea Fertilizer?

Urea is a nitrogen fertilizer with the chemical formula CO(NH₂)₂. It typically contains 46% nitrogen by weight, making it one of the most concentrated solid nitrogen fertilizers used in agriculture. After urea enters the soil, the enzyme urease helps convert it into ammonium. The ammonium can then be converted into nitrate by soil microorganisms under suitable conditions. Plants can take up nitrogen in both ammonium and nitrate forms.

Urea is widely used in field crops, cereals, vegetables, and other agricultural systems because it supplies a large amount of nitrogen in a relatively small quantity of fertilizer. Its main limitation is the risk of ammonia volatilization when urea remains on the soil surface without sufficient rainfall, irrigation, or incorporation. The extent of this loss depends on factors such as temperature, soil pH, moisture, and crop residue.

What Is Ammonium Sulfate Fertilizer?

Ammonium sulfate, with the chemical formula (NH₄)₂SO₄, is a nitrogen and sulfur fertilizer. Standard fertilizer grade commonly contains 21% nitrogen and 24% sulfur, often expressed as 21-0-0-24S. Unlike urea, ammonium sulfate supplies nitrogen in ammonium form from the time it is applied. It also provides sulfur in sulfate form, which plants can take up through their roots.

This combination makes ammonium sulfate useful when a crop requires both nutrients. Its ammonium nitrogen also generally has a lower ammonia-volatilization risk than surface-applied urea under typical conditions, although soil conditions can affect both fertilizers. Ammonium sulfate is available in different physical forms, including crystalline and granular products. The most suitable form depends on the application equipment, handling requirements, and intended use.

Nitrogen Content: Urea vs Ammonium Sulfate

Nitrogen content is one of the most important differences in this nitrogen fertilizer comparison. Urea contains approximately 46% nitrogen, compared with 21% in standard ammonium sulfate. Therefore, urea supplies more than twice as much nitrogen per kilogram of fertilizer. However, a higher nitrogen percentage does not automatically make a fertilizer the better choice. The crop may also need sulfur, and the fertilizer must be managed to reduce nutrient losses.

How Much Fertilizer Is Needed to Supply 100 kg of Nitrogen?

Consider a farmer who needs to supply 100 kg of nitrogen to a field.

Ammonium sulfate: 100 ÷ 0.21 = approximately 476 kg of fertilizer.
Urea: 100 ÷ 0.46 = approximately 217 kg of fertilizer.

These are theoretical quantities based on the stated nitrogen percentages. Actual application rates should follow crop recommendations, soil test results, and the farm’s nutrient management plan. The calculation shows why urea can reduce the amount of product that must be transported, stored, and spread when nitrogen is the only nutrient required.

Ammonium sulfate, however, supplies sulfur as well. If the field also needs sulfur, its additional nutrient value should be included in the comparison.lfur, while urea is better for fast nitrogen in acidic soils or when cost is key. Sometimes, it is better to fertilize agricultural land using a combination of ammonium sulfate and urea. The simultaneous use of these two fertilizers not only reduces the harm of using them separately, but also increases the efficiency of nitrogen absorption.

Compare Cost per Unit of Nutrient

The lowest fertilizer price per ton does not necessarily mean the lowest cost of meeting a crop’s nutrient requirements. When comparing products, consider:

The amount of nitrogen supplied per kilogram.
Whether additional sulfur fertilizer is required.
The cost of transportation, storage, and application.
The risk of nitrogen loss under the planned application conditions.
The fertilizer’s suitability for the crop and soil.

A fair comparison should evaluate the cost of supplying the required nutrients, rather than comparing the price of equal quantities of two different fertilizers.

Sulfur: The Major Difference Between the Two

One of the clearest differences in the ammonium sulfate vs urea fertilizer comparison is sulfur supply. Urea supplies nitrogen, while ammonium sulfate supplies both nitrogen and sulfur. Sulfur is essential for protein formation and several processes involved in plant growth. Although crops need less sulfur than nitrogen in many situations, an insufficient supply can limit growth and yield. Sulfur deficiency may be more likely in certain conditions, including:

Sandy soils with limited sulfur retention.
Soils with low organic matter.
Cropping systems with high nutrient demand.
Fields where harvested crops remove substantial amounts of sulfur.
Crops with relatively high sulfur requirements.

These conditions do not automatically mean that additional sulfur fertilizer is needed. Soil characteristics, crop type, previous fertilizer applications, and nutrient test results should guide the decision. Penn State Extension recommends using soil and plant tissue testing to help assess sulfur needs and identify fields likely to respond to sulfur fertilizer. If testing or agronomic recommendations indicate that both nitrogen and sulfur are required, ammonium sulfate can supply both nutrients in a single application. If sulfur is already sufficient and the crop mainly needs nitrogen, urea may be the more practical option.

Nitrogen Loss and Ammonia Volatilization

Nitrogen loss can affect fertilizer efficiency and increase the amount of nitrogen that fails to reach the crop. One important process is ammonia volatilization, in which nitrogen is lost to the atmosphere as ammonia gas. This is a particular concern with urea when it is applied to the soil surface and left without timely incorporation or sufficient rainfall.

Why Can Surface-Applied Urea Lose Nitrogen?

After urea is applied, it begins to break down through urease activity. This process can temporarily increase pH around the fertilizer granules, creating conditions that favor ammonia formation and loss. The risk is often greater when:

Temperatures are warm.
Soil pH is high.
Urea remains on the soil surface.
Crop residues increase urease activity near the surface.
Rainfall or irrigation is insufficient to move the fertilizer into the soil.

The University of Minnesota Extension explains that incorporating urea into the soil or receiving sufficient rainfall can reduce the risk of ammonia volatilization. The amount of rainfall needed depends on soil and field conditions. When surface application is necessary, growers may also consider a suitable urease inhibitor according to local recommendations and product instructions.

How Does Ammonium Sulfate Compare?

Ammonium sulfate generally has a lower ammonia-volatilization risk than urea when both are surface-applied under typical conditions. Its nitrogen is already in ammonium form, rather than requiring the initial urea breakdown process that creates a localized rise in pH. However, ammonium sulfate is not completely free from nitrogen loss under every condition. Very high soil pH and other unusual conditions can affect ammonia losses. Nitrogen can also be lost through other processes. For example, nitrate formed after soil microorganisms transform ammonium can move below the root zone with excess water or be lost through denitrification under waterlogged conditions. The practical lesson is to match fertilizer choice and application timing to the field’s conditions. Neither product can prevent every form of nitrogen loss.

Ammonium Sulfate vs Urea for Acidic Soil

Soil pH is another important factor when deciding between ammonium sulfate and urea. A common misconception is that urea is always suitable for acidic soil and ammonium sulfate is always preferable for alkaline soil. In practice, both fertilizers can contribute to soil acidification over time, and neither should be selected based on pH alone.

Does Ammonium Sulfate Make Soil More Acidic?

Yes. Ammonium sulfate has a relatively strong acidifying effect as its ammonium nitrogen is transformed in the soil. Repeated applications can gradually lower soil pH, particularly when the amount of fertilizer exceeds crop requirements or soil conditions do not adequately buffer the acidity. This can be useful in some situations, but it can also create problems in soils that are already too acidic.

Is Urea Better for Acidic Soil?

Urea can also contribute to soil acidity over time as its nitrogen is transformed and subsequently undergoes nitrification. Although the initial breakdown of urea can temporarily raise pH around the fertilizer granule, this does not mean that repeated urea applications will make the whole soil more alkaline.

For already-acidic soils, the key question is whether the crop can grow well at the existing pH and whether additional acidification would create a problem. Where soil acidity limits crop growth, lime may be needed to raise pH. The amount should be based on soil testing and the soil’s lime requirement, rather than on pH alone. For more information, read our guide on how to manage acidic soil. When comparing ammonium sulfate vs urea for acidic soil, consider the following:

Already-acidic soil: Evaluate whether further acidification would harm the crop or reduce nutrient availability.
Soil with a high pH: Consider crop needs, sulfur requirements, and the overall nutrient management plan rather than choosing a fertilizer based on pH alone.
Soil with a sulfur deficiency: Ammonium sulfate may be useful if both nitrogen and sulfur are required.
Soil with a confirmed nitrogen requirement but sufficient sulfur: Urea may be suitable if its application and volatilization risks can be managed.

Soil pH, buffering capacity, crop requirements, and the long-term fertilizer program should determine the choice.

When Should You Choose Urea?

Urea may be the better choice when the main objective is to supply nitrogen efficiently and sulfur is not required in the same application. Consider urea when:

The crop primarily needs nitrogen.
Soil or tissue testing indicates that sulfur is sufficient.
High nitrogen concentration is important for transportation and storage.
The farm’s spreading equipment is suited to urea.
The fertilizer can be incorporated or moved into the soil by suitable rainfall or irrigation.
The cost per unit of nitrogen is favorable.

Urea is particularly practical for large agricultural operations where transporting and spreading smaller quantities of concentrated fertilizer offers an advantage. However, its nitrogen concentration should not be the only consideration. If surface-applied urea is likely to experience significant ammonia losses, the cost advantage may be reduced unless appropriate management measures are used.

When Should You Choose Ammonium Sulfate?

Ammonium sulfate may be the better choice when the crop needs both nitrogen and sulfur or when its application characteristics fit the farm’s requirements. Consider ammonium sulfate when:

Both nitrogen and sulfur are required.
Soil or tissue analysis indicates a sulfur deficiency or a likely response to sulfur fertilizer.
A single fertilizer product supplying both nutrients simplifies the nutrient program.
The farm needs a crystalline or granular ammonium sulfate product suited to its equipment.
The application plan benefits from a lower ammonia-volatilization risk than surface-applied urea under comparable conditions.

Standard ammonium sulfate fertilizer contains approximately 21% nitrogen and 24% sulfur. Buyers should check the product specification and certificate of analysis to confirm the actual nutrient content of the supplied grade. Our guide to ammonium sulfate 21-24 grade explains what these figures mean and what buyers should check when evaluating a product. Remember that ammonium sulfate has a relatively strong acidifying effect. Its use should be part of a balanced nutrient management program, especially where soil pH is already low.

Ammonium Sulfate vs Urea: Which One Is Better?

Neither fertilizer is universally better. The right choice depends on what the crop needs and how the fertilizer will perform under the conditions in which it is applied.

Choose urea when a concentrated nitrogen source is the priority, sulfur is already sufficient, and the farm can manage ammonia-volatilization risk.
Choose ammonium sulfate when both nitrogen and sulfur are needed, and the product fits the crop’s nutrient requirements, soil conditions, and application system.

Before making a decision, compare nitrogen concentration, sulfur requirements, soil pH, expected nitrogen losses, product cost, and application expenses. Soil and tissue testing can help establish which nutrients are needed and prevent unnecessary fertilizer use. For farmers and agricultural buyers seeking a nitrogen and sulfur fertilizer, BARNO offers ammonium sulfate products in different physical forms to suit a range of agricultural and handling requirements. Visit our crystalline ammonium sulfate fertilizer page to review product information and specifications.

The best fertilizer is not simply the one with the highest nitrogen percentage or the lowest price per ton. It is the one that supplies the nutrients your crop needs, at the right rate and time, with appropriate management of soil conditions and nutrient losses.