5 Amazing Uses of Ammonium Sulfate Fertilizer | 21-0-0 Fertilizer

If you want to know about the uses of ammonium sulfate fertilizer (21-0-0), you will love this in-depth guide.

But first, let me introduce ammonium sulfate to you.

It is an inorganic salt and its chemical formula is (NH4)2SO4. Here’s a simple chemical reaction to summarise this:

2 NH3 + H2SO4 → (NH4)2SO4

Ammonia + Sulfuric acid → Ammonium sulfate

Now you might be wondering, what does “21-0-0” mean? Let me explain this to you.

What Does “21-0-0” Mean?

This number shows the NPK ratio.

In simple words, it shows the percentage of nitrogen, phosphorus and potassium.

So the ammonium sulfate fertilizer contains:

  • Nitrogen: 21%
  • Phosphorus: 0%
  • Potassium: 0%

Note that it also contains 24% sulfur.

ammonium sulfate fertilizer

Here’s why nitrogen is important for plant growth.


Here’s why 21% nitrogen in ammonium sulfate fertilizer is important.

It is a source of energy for metabolic reactions such as photosynthesis, respiration and nitrogen fixation.

In plants, it causes good leaf growth as well. Can you guess why this is so?

Plants use nitrogen to make proteins, DNA (deoxyribonucleic acid), nucleic acid and amino acids.

Remember that it enhances the function of chlorophyll. Well, what is chlorophyll?

This organelle is responsible for carbohydrate formation through photosynthesis. Now you might be thinking, how do plants obtain nitrogen?

Note that plants cannot take up nitrogen directly from the atmosphere.

It is obtained when ammonia is added to the soil, and the plant takes up nitrogen in the form of NH₄⁺ and NO₃⁻ ions.

They obtain nitrogen in form of nitrates as well. Dead bacteria and animal waste in the soil make this possible.

Now, let’s talk about sulfur.


As we discussed earlier, this fertilizer contains 24% sulfur.

Sulfur (a macro element in plant nutrition) in ammonium sulfate is extremely important. Here’s why.

A Plant makes amino acids, proteins, and oil by using sulfur. Moreover, it is used to form chlorophyll.

It can also activate many vitamins and enzymes. Now, here’s something interesting.

In legume crops, it facilitates nitrogen fixation as well. This is a process in which inert atmospheric nitrogen is converted into more-reactive nitrogen compounds.

These include ammonia, nitrites and nitrates.

Sulfur is absorbed by the plant in the form of sulfate. Pretty simple, isn’t it?

With this, it is time to move on to our next topic.

Uses of Ammonium Sulfate Fertilizer:

If you are planning to use this fertilizer, here are some things that you should consider.

Overview: If we talk about the uses of ammonium sulfate fertilizer, it prevents nitrogen deficiency in your plants. It contains 24% sulfur which is an important component of proteins. It lowers the pH of your soil as well.

Here are some details.

  • It prevents nitrogen deficiency in your plants.

Nitrogen fertilizers such as urea (46-0-0), ammonium nitrate and ammonium sulfate prevent nitrogen deficiency.

Nitrogen deficiency can cause the following problems for your plant:

  1. Slow growth.
  1. Reduced tiller development.
  1. Pale yellowish-green plant.

So remember that less nitrogen can cause wilting and less leaf growth.

  • It is well suited for foliar sprays or making solutions for fertigation.

Let me explain.

uses of ammonium sulfate fertilizer

Let’s say that you conduct a soil test. You find out that your soil is nitrogen deficient. We can use foliar sprays to overcome this.

Using a foliar spray, we apply fertilizers directly to the plants’ leaves (instead of adding them to the soil).

I know that this method cannot replace healthy soil. But, it is important if your plant is suffering from nutrient deficiencies.

Now let me introduce fertigation to you.

Fertigation: In this method, we add fertilizer through irrigation water by the drip system. This method is efficient as nutrients are available readily.

Note that the solubility of ammonium sulfate in water makes this possible.

Amazing, isn’t it?

  • There is no considerable loss of Nitrogen.

To understand this, recall the chemical formula of ammonium sulfate: (NH4)2SO4

This shows that we have ammonium and sulfate ions. To obtain nitrogen, ammonium can be directly taken up by the soil.

Talking about the ammonium portion, it can be lost if it is oxidised to nitrate.

Recall that this nitrogen will make your lawn lusher.

  • It lowers the pH of the soil.

Now you might be wondering, why is that important.

Alkaline soil (pH above 7) is less soluble than neutral or acidic soil. This may cause some plants to have stunted growth or nutrient deficiencies.

Note that elements such as sodium, calcium, and magnesium can make your soil alkaline.

uses of ammonium sulfate fertilizer

The question is, how ammonium sulfate reduces the pH?

This fertilizer is released as small ions which lower the pH of the soil. This is done by replacing alkaline ions like calcium with hydrogen ions.

Note: Elemental sulfur decreases the pH of the soil.

  • It is water-soluble.

Here’s why this is important.

The nutrient levels are not affected by erosion and leaching. Note that leaching is the loss of soluble substances from the top layer of soil.

The best part?

The nutrients are easily available for absorption by plants. Plus they are easy to apply through fertigation.

With water-soluble fertilizers, you can control the precise amount of nutrients available to your plant.

This is extremely important as over-fertilization can damage your plant as well.

  • The amount of nitrogen (21%) makes it an excellent choice for evergreens and growing plants.

We have already discussed the importance of nitrogen for plants.

Although they require other macronutrients such as phosphorus and potassium, the 21-0-0 fertilizer fulfils the nitrogen requirement.

Note: Apart from agriculture, it has some commercial uses as well. For example, it is used for bread products as a dough conditioner.

In the same way, it is a component of fire extinguisher powder. It is used in the chemical, textile and pharmaceutical industries.

Ammonium sulfate vs Urea:

Both of them are nitrogen fertilizers. But, which one is better?

Here’s everything that you should know.

  • NPK ratio.

Ammonium sulfate (AS) contains 21% nitrogen while urea contains 46% nitrogen.

Does higher nitrogen content mean that urea is better?


If you over-apply nitrogen, the ability of your plant to produce fruit and flowers can be reduced. So you have to be careful when applying urea.

Therefore, this will depend on your soil condition.

  • The urea fertilizer can lose nitrogen more rapidly in the atmosphere.

Point to remember: If applied incorrectly, 40% of Nitrogen can be vaporized and lost as a gas. So, ammonium sulfate fertilizer (21-0-0) is more stable.

As we have already discussed, urea is not as stable as other solid nitrogenous fertilizers. So, it even decomposes at room temperature.

This is because it can react with water to form unstable ammonium carbonate.

In short, both of these fertilizers are good sources of nitrogen. You can select either of them according to your requirement.

With this, it is time to move on straight to the next topic.

How and When to Apply Ammonium Sulfate Fertilizer?

When applying fertilizers, you have to be careful. This is because over-application can damage your plant.

So here’s the step-by-step guide.

  • Conduct a soil test.

This is the first thing that you should consider.

As the word suggests, soil testing tells the expected growth potential. Here’s what I mean.

This test will help you identify the level of nitrogen in your soil. In this way, you can determine the amount of fertilizer you need.

  • Apply in early spring or late summer.

Note that the application process depends on your soil condition.

For the best application rates, follow the instructions on the package carefully.

In general, this fertilizer stays in the soil for 4-6 weeks (28-42 days). So you can re-apply it after 45-60 days.

  • In some cases, you should avoid using it in late fall.

Here’s a thing.

Fall applications have a greater risk of loss of nitrogen. So here’s what you should do.

For cool season grasses: For grasses like Kentucky Bluegrass, Fescue and Ryegrass, you can use nitrogen fertilizers in spring and fall.

For warm season grasses: For grasses like St. Augustine and Bermuda, use nitrogen fertilizers throughout summer.

The idea is that the demand for nitrogen is high during the late vegetative and early reproductive stages.

when to apply ammonium sulfate fertilizer

So you should plan your fertilizer application properly.

  • If you are applying the fertilizer in granular form, spread it evenly by hand.

You can also use a fertilizer spreader. When applying, spread it in a circular manner (away from any exposed roots).

  • You will need 5 to 6lbs of ammonium sulfate per 1000 square feet (with an equal amount of compost).

You should apply this mixture to your lawn when it’s dry.

Then, water it thoroughly for 15 minutes after the application. This will ensure that the nutrients reach the root system of the plant.

In granular form, you should apply it 4 times annually.

In liquid form, 3 tablespoons ammonium sulfate for 1 gallon of water is enough. Here’s why watering is important.

If ammonium sulfate dries on your grass, it can “burn” it as well.

Further reading:

A Step-by-Step Guide on Fertilizing Your Lawn in Texas

Now, let’s move straight to our next topic.

Can I Use Ammonium Sulfate Fertilizer For Onions?

The quick answer is yes.

The first thing that you should know is that onions have a high nitrogen requirement.

The problem is that they have a low nutrient uptake efficiency due to the shallow root system. So, you should sow the seed in mid to late October.

At this stage, a phosphorus fertilizer such as 0-20-0 is a good choice. This is because phosphorus improves the root system.

When the onions are established, you can use ammonium sulfate or ammonium nitrate fertilizer to provide nitrogen.

In general, you should apply one cup of ammonium sulfate per twenty feet of row. You can use it every 2-3 weeks as well.

The takeaway: To from large bulbs, side-dress the plant in early and mid-summer.

For alkaline soils, you can use ammonium sulfate. But for acidic soils, ammonium nitrate is a good choice.

Now, let’s talk about wheat.

Can I Use 21-0-0 Fertilizer For Wheat?

To fulfil the nitrogen requirement, it can be an excellent choice.

Let me explain.

Wheat plantation usually starts in early spring or mid-March. At this time, it starts to grow rapidly.

Remember that wheat is highly responsive to starter fertilizers such as nitrogen and phosphorus.

So the NPK 21-0-0 fertilizer can be applied at this stage. Over here, I want to talk about sulfur as well.

The sulfur provided by the ammonium sulfate fertilizer is an important component of proteins. Without adequate sulfur, the wheat crop may not reach its full potential.

In simple words, this fertilizer will give an initial boost.

Now you might be wondering, can I use urea as well?

Yes, you can. But, it does not provide sulfur. So in some cases, ammonium sulfate is the best choice.

Can I Use Ammonium Sulfate Fertilizer For Tomatoes:

The first thing is that growing tomatoes can be challenging.

But, let me make this simple for you.

Usually, they need high phosphorus fertilizers such as 6-24-24 and 8-32-16. You have to be extremely careful when applying these.

As we have already discussed, over-application can destroy your plant. We also talked about how phosphorus is involved in root growth.

Over time, fertilizers such as 8-8-8 and 12-4-8 can be used.

ammonium sulfate fertilizer for tomatoes

During the fruiting stages, ammonium sulfate is an excellent choice for tomatoes. This is because of the 21% nitrogen and 24% sulfur content.

Note that the ideal pH in which tomatoes grow is 5.5-7.5. So if your soil is alkaline, ammonium sulfate can reduce it as well.

Now, let’s talk about vegetables.

Can I Use Ammonium Sulfate Fertilizer For Vegetables:

Yes, you can. Here’s what you should know.

  • The nitrogen content in this fertilizer makes it a good choice for vegetables.

The idea is that vegetables need nitrogen and sulfur for protein formation and photosynthesis.

  • Vegetables consume a lot of nutrients.

Yes, vegetables need a lot of nutrients. They obtain it from the soil quickly.

This makes this fertilizer a good fit for vegetables.

In other words, it provides lost nutrients. This causes vegetables to grow in a better manner.

So, this fertilizer can improve the harvest and the overall health of your plant.

Note: Apart from nitrogen and sulfur, they require nutrients such as phosphorus and potassium as well.

Wrapping Up:

So, there you have it.

This was an in-depth guide on the ammonium sulfate fertilizer (21-0-0).

To recap, this fertilizer is a great source of Nitrogen.

But you should be careful when applying it. This is because over-application can lead to stunted growth.

You can use this fertilizer to grow onions, vegetables, tomatoes and wheat. Plus, it is good for acid-loving plants such as blueberries, artichokes, or potatoes.

Thank you for reading and staying with me till the end. If you have any questions, feel free to get in touch.

Stay tuned for more.

5 Amazing Uses of Ammonium Sulfate Fertilizer | 21-0-0 Fertilizer

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