How to Combine Ammonium Sulfate With Other Fertilizers

Ammonium sulfate is a nitrogen and sulfur fertilizer that can play an important role in crop nutrition. However, these two nutrients are not always enough to meet a crop’s full requirements. Depending on the soil, crop type, and growth stage, farmers may also need phosphorus, potassium, or other essential nutrients. Choosing the right ammonium sulfate fertilizer combinations can help meet these requirements without applying unnecessary fertilizer. For example, ammonium sulfate can supply nitrogen and sulfur, while diammonium phosphate (DAP) provides phosphorus and additional nitrogen. Potassium fertilizers can supply another nutrient that ammonium sulfate does not contain.

The key is to build a balanced fertilizer program based on crop needs and soil conditions. Combining products is not automatically better than applying a single fertilizer, and the correct nutrient balance matters more than the number of products used. This guide explains how ammonium sulfate fits into a fertilizer program, when to consider using it alongside urea, DAP, NPK, and potassium fertilizers, and what to check before combining or applying these products.

Why Combine Ammonium Sulfate With Other Fertilizers?

Ammonium sulfate typically contains approximately 21% nitrogen (N) and 24% sulfur (S), although the guaranteed analysis on the product label should always be checked. It supplies these nutrients in forms that can support plant growth and protein production. Nitrogen supports leaf development, chlorophyll formation, and overall vegetative growth. Sulfur is needed for protein synthesis, enzyme activity, and several other plant processes. However, ammonium sulfate does not supply phosphorus or potassium. These nutrients have different roles in plant development:

• Phosphorus (P): Supports energy transfer, root development, and reproductive growth.
• Potassium (K): Helps regulate water balance, supports enzyme activity, and improves plant stress tolerance.
• Nitrogen and sulfur (N and S): Support growth and protein formation through different but complementary functions.

If a soil test or crop recommendation indicates a need for phosphorus or potassium, another fertilizer may be necessary. For example, a farmer might use ammonium sulfate to supply nitrogen and sulfur and select DAP to meet a phosphorus requirement. However, if the soil already contains sufficient phosphorus and potassium, adding these nutrients without a clear need can increase costs and contribute to nutrient losses. Penn State Extension recommends selecting fertilizer analyses that match soil-test recommendations rather than adding nutrients that are already sufficient. Therefore, the purpose of ammonium sulfate fertilizer combinations is to meet specific nutrient requirements, not simply to apply more fertilizer.

Ammonium Sulfate + Urea

Urea is a widely used nitrogen fertilizer, typically containing 46% nitrogen. Unlike ammonium sulfate, it does not provide a significant amount of sulfur. Combining ammonium sulfate with urea can therefore be useful when a crop needs both nitrogen and sulfur but requires more nitrogen than ammonium sulfate alone can economically supply.

When should you use both?

This combination may be appropriate when:

• The crop needs additional nitrogen but also requires sulfur.
• The soil or crop nutrient plan indicates that nitrogen demand exceeds the amount that should be supplied through ammonium sulfate.
• A fertilizer program needs to balance nitrogen and sulfur inputs.
• Local fertilizer prices and application costs make using both products a practical option.

For example, a grower may use ammonium sulfate to meet part of the nitrogen requirement while supplying the remaining nitrogen through urea. The correct proportions depend on the total nitrogen and sulfur requirements, existing soil fertility, and the characteristics of the fertilizer products.

Can ammonium sulfate be mixed with urea?

Dry ammonium sulfate and urea may be physically blended when the specific products and blending conditions are suitable. However, compatibility should not be assumed for every formulation or storage condition. Moisture, particle size, storage time, and the physical properties of each product can affect blend quality. If the products absorb moisture or have significantly different particle sizes, the blend may cake or separate during handling.

The most important agronomic precaution is to calculate the total nitrogen supplied by both products. Applying the full recommended nitrogen rate through urea and then adding ammonium sulfate without adjusting the rate can result in excessive nitrogen. For a closer comparison of their nutrient profiles, costs, and uses, see our guide on ammonium sulfate vs urea.

Ammonium Sulfate + DAP

Diammonium phosphate (DAP) is a nitrogen-phosphorus fertilizer commonly labeled 18-46-0. This means it typically contains 18% nitrogen, 46% phosphate expressed as P₂O₅, and no potassium. Ammonium sulfate supplies nitrogen and sulfur, while DAP supplies nitrogen and phosphorus. Together, they can provide all three nutrients: nitrogen, phosphorus, and sulfur.

When is this combination useful?

Ammonium sulfate with DAP may be suitable when soil tests and crop recommendations indicate a need for both phosphorus and sulfur, along with nitrogen. For example, a crop may require phosphorus for early root development while also needing nitrogen for growth and sulfur for protein formation. Using both fertilizers can help meet these requirements through a planned nutrient program.

However, this does not mean every crop needs all three nutrients at the same time. If phosphorus levels are already adequate, adding DAP may be unnecessary. Likewise, if sulfur requirements are already met, ammonium sulfate may not be the most suitable nitrogen source.

How should the application rate be calculated?

Calculate the required amounts of nitrogen, phosphorus, and sulfur before choosing the proportions of each product. Both DAP and ammonium sulfate contribute nitrogen, so their nitrogen content must be counted together. Also consider fertilizer placement. DAP can release ammonia under certain soil conditions, and excessive rates or placement too close to seeds can injure germinating seeds and seedlings. Follow crop-specific recommendations for rate and placement. The goal is to supply the required nutrients without creating an imbalance or exposing young plants to excessive fertilizer concentrations.

Ammonium Sulfate + NPK Fertilizers

NPK fertilizers contain nitrogen, phosphorus, and potassium in different proportions. Their nutrient ratios vary, so the product label is essential when planning an ammonium sulfate fertilizer mix. Adding ammonium sulfate to an NPK fertilizer may make sense when the existing NPK formulation does not supply enough nitrogen or sulfur for the crop’s requirements. For example, an NPK fertilizer may supply the recommended phosphorus and potassium, while ammonium sulfate provides additional sulfur and part of the nitrogen requirement.

When is additional ammonium sulfate unnecessary?

An NPK fertilizer may already supply enough nitrogen for a particular crop and application stage. Adding ammonium sulfate without adjusting the NPK rate can increase the total nitrogen input beyond what is needed. The same applies to sulfur. If the NPK product or another fertilizer already supplies sufficient sulfur, additional ammonium sulfate may increase costs without providing a meaningful benefit. Before choosing ammonium sulfate with NPK, check:

1. The NPK fertilizer’s guaranteed nutrient analysis.
2. The crop’s total nitrogen, phosphorus, potassium, and sulfur requirements.
3. The nutrients already available in the soil.
4. The contribution from previous fertilizer applications and other nutrient sources.
5. The total amount of each nutrient supplied by the proposed combination.

For a more detailed comparison of fertilizer nutrient ratios, see our guide to ammonium sulfate vs NPK fertilizers.

Ammonium Sulfate + Potassium Fertilizers

Potassium fertilizers can complement ammonium sulfate when a crop requires nitrogen, sulfur, and potassium. One option is potassium sulfate, which supplies potassium and sulfur but does not provide nitrogen. When used with ammonium sulfate, it can provide a combination of N, K, and S. This may be useful for crops that need potassium for water regulation, enzyme activity, and crop development while also requiring nitrogen and sulfur.

Is potassium sulfate always the best choice?

Not necessarily. Potassium sulfate may be appropriate when both potassium and sulfur are required, but other potassium fertilizers may be more suitable depending on crop sensitivity, soil conditions, and the nutrient recommendation. For example, potassium chloride supplies potassium but also adds chloride. Whether that is appropriate depends on the crop’s tolerance to chloride and the soil’s salinity conditions.

Potassium sulfate supplies additional sulfur, so this contribution must be included in the total sulfur calculation. If the crop does not need more sulfur, another potassium source may provide a better nutrient balance. Compare the cost per unit of the required nutrient, the product’s nutrient analysis, and the expected agronomic benefit before choosing a combination. Our guide to ammonium sulfate vs. potassium sulfate can help explain the differences between these products.

Can Ammonium Sulfate Be Mixed With Every Fertilizer?

No. Agronomic suitability and physical or chemical compatibility are two separate questions. Two fertilizers may supply complementary nutrients but still be unsuitable for mixing under certain conditions. Compatibility depends on the product formulations, moisture content, mixing method, water quality, concentration, and storage conditions. A dry blend, a solution prepared in water, and a concentrated stock solution used for fertigation do not behave in the same way.

For example, calcium-containing fertilizers can react with sulfate or phosphate sources in concentrated stock solutions, potentially forming precipitates that block irrigation equipment. Penn State Extension advises keeping calcium separate from phosphate and sulfate sources in concentrated stock solutions. A combination that works as a dry blend may therefore be unsuitable for a concentrated irrigation solution. Before mixing products, consult the manufacturer’s technical guidance and check whether the proposed combination is approved for the intended application method.

For detailed rules on fertilizer compatibility, dry blending, tank mixing, and precipitation, see our guide, fertilizer compatibility, that covers the broader mixing question, while this guide focuses on choosing ammonium sulfate combinations for crop nutrition.

Dry Blending vs. Dissolving in Water

The way fertilizers are combined affects their handling and application.

Dry fertilizer blending

When blending granular or crystalline fertilizers, consider particle size, particle density, moisture content, and storage conditions. Products with different particle sizes can separate during transportation or handling. This can result in uneven nutrient distribution, even when the original blend was prepared correctly.

Moisture can also cause caking and reduce the flow of fertilizer through application equipment. Use suitable products, follow supplier recommendations, and avoid prolonged storage under damp conditions. A physically uniform blend is important because each portion should deliver the intended nutrient ratio.

Fertilizer solutions and fertigation

When fertilizers are dissolved in water, solubility and precipitation become important. A product that dissolves well on its own may react with another fertilizer when concentrated solutions are combined. Water quality, temperature, solution concentration, and the presence of calcium or other dissolved minerals can affect the result.

For fertigation, check the solubility of each fertilizer and confirm compatibility at the intended concentration. Separate stock tanks may be necessary when fertilizers cannot safely be stored together in concentrated form. Do not assume that a successful small-scale mixture guarantees safe performance in an irrigation system. Follow product instructions and consult a qualified agronomist or fertilizer supplier when needed.

How to Build a Fertilizer Program With Ammonium Sulfate

A good fertilizer program starts with nutrient requirements rather than a list of products to mix. Follow these steps to decide whether ammonium sulfate belongs in your program.

1. Conduct agricultural soil testing: Use a suitable soil test to assess nutrient availability and soil pH. Interpret the results using recommendations appropriate for the crop, soil type, and local growing conditions.
2. Identify the crop’s nutrient requirements: Determine how much nitrogen, phosphorus, potassium, and sulfur the crop needs. Consider its growth stage, expected yield, and any crop-specific nutrient recommendations.
3. Decide whether ammonium sulfate is appropriate: Choose ammonium sulfate when its nitrogen and sulfur contribution matches the nutrient plan. Also consider its effect on soil pH over time, particularly in soils already prone to acidity.
4. Select additional fertilizers only for nutrients still needed: Use urea if additional nitrogen is required, DAP if phosphorus is needed, or a suitable potassium fertilizer if potassium is lacking. NPK fertilizers may be appropriate when several nutrients are required together.
5. Calculate the total nutrient contribution: Count the nitrogen supplied by every product and account for the phosphorus, potassium, and sulfur supplied by the complete fertilizer program. Avoid applying the same nutrient twice without adjusting the rates.
6. Check product compatibility: Confirm that the products can be blended, dissolved, stored, or applied together using the intended method.
7. Apply according to crop and product recommendations: Follow the recommended rates, timing, placement, and handling instructions. Review the program when soil test results, crop conditions, or production goals change.

This process helps ensure that ammonium sulfate fertilizer combinations serve a clear agronomic purpose rather than increasing fertilizer use unnecessarily.

Common Mistakes When Combining Ammonium Sulfate With Other Fertilizers

Even a suitable combination can produce poor results when nutrient calculations or application methods are incorrect. Avoid these common mistakes:

• Ignoring total nitrogen: Urea, DAP, NPK, and ammonium sulfate may all contribute nitrogen. Calculate the total before applying them together.
• Adding sulfur without checking requirements: Ammonium sulfate and potassium sulfate both supply sulfur. Their combined contribution may exceed the crop’s needs.
• Applying unnecessary phosphorus or potassium: Do not add nutrients simply because a fertilizer combination contains them. Base decisions on soil tests and crop recommendations.
• Assuming every combination is compatible: Agronomic suitability does not guarantee that products can be safely mixed in a dry blend or concentrated solution.
• Overlooking soil pH: Repeated ammonium sulfate applications can contribute to soil acidification. Monitor soil pH and manage acidity when necessary.
• Using the same rate for every crop: Nutrient requirements vary with crop species, soil conditions, yield goals, and growth stage.

Avoiding these mistakes can improve fertilizer efficiency, reduce unnecessary input costs, and support more balanced crop nutrition.

Final Thoughts

The most effective ammonium sulfate fertilizer combinations are those that meet a clear nutrient requirement. Ammonium sulfate can complement urea when additional nitrogen is needed alongside sulfur, DAP when phosphorus is required, NPK when its nutrient balance needs adjustment, and potassium fertilizers when crops require additional potassium.

However, no combination is automatically suitable for every field or crop. Soil testing, nutrient calculations, product compatibility, and appropriate application practices should guide the decision. For farmers and fertilizer buyers, the objective is straightforward: supply the nutrients the crop needs, in the right amounts and at the right time, without unnecessary fertilizer use.

If you are sourcing ammonium sulfate for agricultural applications, review the product specifications and select a grade suited to your fertilizer program. Contact BARNO to discuss crystalline ammonium sulfate supply for your agricultural fertilizer requirements.