Ammonium sulphate is one of the most widely used inorganic fertilizers. This article provides a detailed overview of ammonium sulphate, its role as a nitrogen and sulphur fertilizer, and best practices for application in agriculture and horticulture.
As a premium soluble nitrogen and sulphur fertilizer, ammonium sulphate offers significant benefits which make it a popular choice for farmers and growers. Read on to learn more about maximizing the performance of this versatile compound.
What is Ammonium Sulphate?
Ammonium sulphate is an inorganic salt made up of 21% nitrogen and 24% sulphur by weight. Its chemical name is ammonium sulfate [(NH4)2SO4] and it possesses a highly soluble, crystalline form.
The manufacturing process involves reacting ammonia gas with sulphuric acid to produce a precipitated white powder. Granulating or crystallizing the powder results in the final pelletized product.
Key properties that underpin the usefulness of ammonium sulphate fertilizer include:
- An immediately available source of nitrogen and sulphur for rapid plant uptake
- 100% water soluble and non-volatile ammonium nitrogen form
- Soil acidifying effect from the sulphur content
- Compatibility with most pesticides and liquid fertilizer blends
- Low risk of leaching or runoff compared to other nitrogen sources
- Cost effectiveness as a straight nitrogen fertilizer
With these beneficial characteristics, ammonium sulphate is widely applied in broadacre cropping, pastures, horticulture, turf and other farming systems.
Why is it an Effective Fertilizer?
The sulphate form of ammonium nitrogen offers important advantages that enhance ammonium sulphate’s efficacy as a fertilizer.
Firstly, since the nitrogen is present as ammonium rather than nitrate, it is not prone to leaching or loss through denitrification. Secondly, the sulphur content boosts overall nutrient availability for plants.
Some key benefits include:
- Readily available nitrogen – Present in the ammonium form which is instantly usable by plants upon application.
- Non-volatile – Ammonium nitrogen does not volatilize or convert to gaseous compounds when broadcast, unlike urea.
- Acidifying effect – The sulphur content reacts in soil to lower pH over time. This aids availability of certain nutrients.
- Sulphur supply – An economical sulphur source, important for plant growth and as a soil conditioner.
- Chloride-free – Unlike some nitrogen fertilizers, contains no chloride which can adversely accumulate in soils.
- Compatible – Can be blended with other liquid or granular NPK fertilizers or applied concurrently with pesticides.
With a nitrogen to sulphur ratio of 2:1, ammonium sulphate is an efficient choice for delivering both of these key macronutrients.
How is Ammonium Sulphate Applied?
Ammonium sulphate fertilizer is suitable for solid broadcast application or liquid application via fertigation systems. Granular ammonium sulphate contains a minimum of 99% dry matter and spreads evenly.
- Broadcast application – Evenly apply granular ammonium sulphate fertilizer to the soil surface pre-planting or as a top dressing. Lightly water in to move nutrients into the root zone.
- Fertigation – Soluble ammonium sulphate is ideal for application through irrigation systems. Delivers a consistent nutrient supply directly to the root zone.
- Foliar sprays – Dilute rates can be foliar applied but are generally less efficient than soil application. Foliar uptake risks leaf burn without adequate dilution.
Ammonium sulphate is highly water soluble so does not require extended watering in to take effect. It can be blended with other fertilizers to create custom NPK blends.
Ammonium Sulphate Use Rates
Recommended application rates for ammonium sulphate depend on factors like soil conditions, crop type, growth stage and yield targets. Some typical use rates include:
- Cereal crops – 50-150 kg/ha
- Pasture – 50-100 kg/ha
- Cotton – 150-250 kg/ha
- Sugarcane – 100-250 kg/ha
- Turf – 25-75 g/m2
- Vegetables – 250-500 kg/ha
- Tree crops/vines – 250-600 kg/ha
Always follow manufacturer guidelines on maximum application rates. Excess nitrogen can cause issues like lodging and burning. Split applications spaced through the season are generally more efficient than a single large application.
Which Crops Respond Well to Ammonium Sulphate?
The rapid nitrogen supply suits high nitrogen-demanding crops while the sulphur boosts growth and quality. Crops that commonly receive ammonium sulphate fertilizer include:
- Cereals – Wheat, barley, oats, sorghum
- Cotton
- Sugarcane
- Corn
- Pasture grasses
- Brassicas – Canola, cabbage, broccoli
- Alliums – Onions, leeks, garlic
- Legumes – Soybeans, peas, lentils
- Root vegetables – Carrots, potatoes, sweet potato
- Tree fruits and vines
- Ornamentals and turf
Leafy crops often show strong yield and quality responses from the combined nitrogen and sulphur nutrition provided by ammonium sulphate.
When Should You Apply Ammonium Sulphate?
Timing of fertilizer applications is an important factor in getting the most value from ammonium sulphate.
- Pre-plant – Apply and incorporate before planting to support early root and crop establishment.
- Post-emergent – Top dress after emergence, Before stem elongation provides nitrogen for rapid growth.
- Fertigation – Frequent low dose applications through irrigation during rapid bulking delivers a steady nutrient supply.
- Post-harvest – Autumn application emphasizes nitrogen storage in vegetative parts for yield next season.
- Avoid hot conditions – Evaporation can lead to fertilizer burning leaves or roots in extreme heat.
Paying close attention to crop demand and seasonal conditions will optimize fertilizer efficiency.
Are There any Risks or Downsides to Ammonium Sulphate Use?
When used correctly ammonium sulphate is a safe and reliable fertilizer. However, some potential issues to be aware of include:
- Overuse can push soil acidity too low over time
- Nitrogen loss through leaching if excessively applied
- Potential root or leaf burn if applied at very high rates
- Contains no nutrients besides nitrogen and sulphur
- Less concentrated than some nitrogen fertilizers
Following manufacturer guidelines on rates, paying attention to soil pH changes and alternating with other nutrient sources helps avoid most risks.
FAQ
Q: What is ammonium sulphate fertiliser and why is it considered a fertiliser rich in nitrogen?
A: Ammonium sulphate is a chemical compound with the formula (NH4)2SO4 that serves as an excellent fertiliser rich in nitrogen (21%) and sulphur (24%). It’s produced by reacting ammonia with sulfuric acid. The nitrogen component stimulates and promotes leaf growth in all plants, making it particularly beneficial for greening up lawns and growing leaf crop vegetables. The high nitrogen content supports protein production in plants, while the sulphur improves overall plant health and helps with nitrogen utilization. Its crystal structure makes it free flowing and easy to apply, with particles that dissolve quickly when water-soluble.
Q: How should I apply ammonium sulphate to my lawn and garden?
A: For proper application of ammonium sulphate, apply 20-30g per square metre for lawns when actively growing. For garden beds, use 30-40g per square metre, working it into the soil. When applying to established plants, spread it around the drip line and water in well. For potted plants, use a diluted solution (about 1 teaspoon per gallon of water). Apply during the growing season, preferably in spring and early summer to maximize leaf growth. Always water thoroughly after application to prevent burning and ensure the fertiliser dissolves properly. For greening up lawns quickly, it can be applied as a dilute foliar spray for faster results.
Q: What chemical reaction occurs when using ammonium sulphate in soil?
A: When using ammonium sulphate in soil, several important reactions occur. First, the ammonium ions (NH4+) undergo nitrification, where soil microbes convert them to nitrate (NO3-), making nitrogen available to plants. This microbial reaction releases hydrogen ions, creating an acidifying effect that lowers soil pH. In alkaline soils, this reaction is beneficial as it helps balance the pH and improves nutrient availability. The sulfate component reacts with soil particles to release sulphur, which plants use for protein synthesis. In calcium-rich soils, ammonium sulphate may react to form gypsum (calcium sulfate), which improves soil structure. These reactions contribute to its effectiveness as a fertiliser while simultaneously affecting soil chemistry.
Q: What are the main properties of ammonium sulphate that make it an effective fertiliser?
A: Ammonium sulphate’s key properties include its high nitrogen content (21%) that stimulates leaf growth, combined with valuable sulphur (24%) that aids in protein synthesis and chlorophyll production. It’s highly soluble in water, ensuring nutrients are quickly available to plants. Its crystalline, powdered form allows for uniform application and good storage properties. Unlike ammonium nitrate, it has lower fire hazard while maintaining excellent free flowing properties even in humid conditions. It performs well across different temperature ranges and has minimal volatilization losses. The fertiliser’s acidifying property makes it ideal for alkaline soils and helps in the availability of micronutrients like iron and magnesium. Additionally, it has minimal impact on beneficial soil microorganisms when used correctly.
Q: How does ammonium sulphate compare to other nitrogen fertilisers like ammonium nitrate?
A: Compared to ammonium nitrate, ammonium sulphate contains less nitrogen (21% vs 34%), but provides additional sulphur (24%) which ammonium nitrate lacks. Ammonium sulphate has a stronger acidifying effect on soil, making it better for alkaline soils but potentially problematic in already acidic conditions. It’s considered safer to store and transport than ammonium nitrate, which has explosive properties. While both are water-soluble, ammonium sulphate may be slower to leach through soil. Both fertilisers stimulate and promotes leaf growth effectively, but ammonium sulphate is often preferred for crops with higher sulphur requirements or when trying to discourage certain weeds like clover in lawns. Temperature and moisture affect both, but ammonium sulphate tends to be more stable across varying environmental conditions.
Q: Can ammonium sulphate be used for all types of plants, and are there any that particularly benefit from its application?
A: Ammonium sulphate can be used for most plants, but it’s especially beneficial for acid-loving plants like azaleas, rhododendrons, blueberries, and potatoes. Grasses and especially leaf crop vegetables like spinach, kale, and lettuce respond exceptionally well to its nitrogen content, which stimulates and promotes leaf growth. Brassicas (cabbage, broccoli) benefit from both its nitrogen and sulphur components. When used for greening up lawns, it produces quick results while discouraging clover and some broadleaf weeds. Plants that need strong vegetative growth and dark green foliage will show dramatic improvement. However, it should be used cautiously with plants that prefer alkaline soils or are sensitive to high nitrogen levels, such as many flowering plants where excessive leaf growth might come at the expense of blooms.
Q: What precautions should I take when using ammonium sulphate fertiliser?
A: When using ammonium sulphate, wear gloves and eye protection as it can irritate skin and eyes. Avoid application during hot, dry conditions to prevent burning plants. Always water in well after application to dissolve the crystal particles and prevent fertiliser burn. Monitor soil pH regularly, as repeated applications can increase acidity, especially in soils with low buffering capacity. Keep the fertiliser away from plant stems and foliage, and never exceed recommended application rates (generally 20-30g per square metre for lawns). Store in a cool, dry place away from children and pets. Due to its reaction with alkaline materials, don’t mix with lime or wood ash. Be aware that excessive use may lead to nutrient imbalance, affecting calcium and magnesium uptake. Consider supplementing with potassium if using regularly, as ammonium sulphate doesn’t contain this essential nutrient.
Q: What is the history and manufacturing process of sulphate of ammonia?
A: Ammonium sulphate was first widely used as a fertiliser in the 19th century. It was initially produced as a byproduct of coal gas production and coal coking for the steel industry. The traditional manufacturing process involves the reaction between ammonia and sulfuric acid, which creates crystal formations of ammonium sulphate. Today, much of the world’s supply is produced as a byproduct of caprolactam (nylon) manufacturing. The synthetic process creates a high-purity, free flowing product with consistent particle size. Modern production methods have improved the fertiliser’s quality and reduced impurities. The resulting powdered or granular fertiliser contains approximately 21% nitrogen and 24% sulphur, making it an efficient dual-nutrient product. This manufacturing history explains why ammonium sulphate has long been one of the most widely available and economical nitrogen fertilisers globally.
Key Takeaways on Ammonium Sulphate Fertilizer
- Provides an immediately plant-available nitrogen and sulphur source
- Rapid uptake promotes leafy growth and plant quality
- Ammonium nitrogen form resists leaching and volatilization losses
- Useful asset for fertigation systems due to high solubility
- Works well blended with other NPK fertilizers
- Leafy crops, cereals and high N-demand plants respond best
- Apply before planting, during early growth or through peak demand
- Moderate rates split through the season provide optimal efficiency
With both nitrogen and sulphur deficiency increasingly common in soils worldwide, ammonium sulphate is a valuable fertilizer option. Follow best practice guidelines to harness the benefits it provides for agricultural and horticultural productivity.