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How to Optimize Ammonium Sulfate Fertilization by Soil pH

Soil pH plays a critical role in the effectiveness of ammonium sulfate fertilization. As a nitrogen and sulfur fertilizer with an acidifying effect, ammonium sulfate shows different nutrient behaviors and nitrogen efficiency across acidic, neutral, and alkaline soils.

This article explains how soil pH influences ammonium sulfate performance and provides practical, pH-based fertilization strategies to improve nitrogen use efficiency, reduce ammonia volatilization, and support sustainable crop nutrition, with technical insights from Risso.

1. Why Soil pH Matters in Ammonium Sulfate Fertilization
1. Why Soil pH Matters in Ammonium Sulfate Fertilization

2. How Ammonium Sulfate Interacts with Soil pH
2. How Ammonium Sulfate Interacts with Soil pH

3. Optimized Ammonium Sulfate Application Strategies for Different Soil pH Levels
3. Optimized Ammonium Sulfate Application Strategies for Different Soil pH Levels

4. Soil pH, Ammonia Volatilization, and Nitrogen Use Efficiency
4. Soil pH, Ammonia Volatilization, and Nitrogen Use Efficiency

5. Practical Recommendations for pH-Based Fertilizer Management
5. Practical Recommendations for pH-Based Fertilizer Management

6. Conclusion: Toward Precision Fertilization Based on Soil pH
6. Conclusion: Toward Precision Fertilization Based on Soil pH

1. Why Soil pH Matters in Ammonium Sulfate Fertilization

Soil pH is one of the most influential factors affecting nutrient availability, microbial activity, and fertilizer efficiency. For nitrogen and sulfur fertilizers, pH determines how nutrients transform in the soil and how effectively crops can absorb them.

Ammonium sulfate fertilizer, valued for supplying ammonium nitrogen (N) and sulfur (S) simultaneously, performs very differently across acidic, neutral, and alkaline soils. Understanding this interaction allows growers and fertilizer professionals to design more efficient, economical, and environmentally responsible fertilization programs.

2. How Ammonium Sulfate Interacts with Soil pH

After application, ammonium sulfate dissolves readily in soil moisture, releasing ammonium ions (NH₄⁺) and sulfate ions (SO₄²⁻). The ammonium fraction undergoes nitrification, a microbial process converting NH₄⁺ into nitrate (NO₃⁻). During this process, hydrogen ions (H⁺) are released, which gradually lowers soil pH.

Because of this reaction pathway, ammonium sulfate is classified as a physiologically acidic fertilizer. Its acidifying effect can be beneficial in alkaline soils but may pose risks in already acidic environments if not properly managed.

3. Optimized Ammonium Sulfate Application Strategies for Different Soil pH Levels

3.1 Ammonium Sulfate in Acidic Soils (pH < 6.5)

In acidic soils, excessive application of ammonium sulfate can further decrease soil pH, potentially increasing aluminum and manganese availability to toxic levels. This may restrict root development and reduce nutrient uptake efficiency.

Recommended management approach:

Use ammonium sulfate as a supplemental nitrogen and sulfur source, rather than the sole nitrogen fertilizer
Avoid continuous high-rate applications over multiple seasons
Combine with liming materials to buffer soil acidity when long-term use is required
Consider integrating nitrate-based or neutral nitrogen fertilizers to maintain nutrient balance

3.2 Ammonium Sulfate in Neutral Soils (pH 6.5–7.5)

Neutral soils provide one of the most favorable environments for ammonium sulfate fertilizer application. In this pH range, the soil’s buffering capacity moderates acidification, allowing ammonium sulfate to deliver stable and predictable nutrient performance.

In practice, ammonium sulfate is particularly effective in neutral soils for crops with high sulfur demand, such as oilseeds, cereals, and many cash crops. Strategic placement as a basal fertilizer or during early vegetative growth stages can significantly improve nitrogen use efficiency.

Many fertilizer programs developed by Risso for international markets are designed around this pH range, where ammonium sulfate demonstrates both agronomic reliability and economic value.

3.3 Ammonium Sulfate in Alkaline and Calcareous Soils (pH > 7.5)

Alkaline and calcareous soils present a unique challenge. Under high pH conditions, ammonium nitrogen is more susceptible to ammonia volatilization, especially when fertilizer is surface-applied. Nitrogen losses can be substantial, reducing fertilizer efficiency and increasing environmental emissions.

Effective risk-mitigation strategies include:

Deep placement or band application to limit surface exposure
Immediate irrigation or application before rainfall
Combining ammonium sulfate with neutral or slow-release fertilizers
Avoiding application during hot, dry, and windy conditions

When managed properly, ammonium sulfate can still serve as a useful nitrogen and sulfur source in alkaline soils, while also contributing to gradual pH adjustment.

4. Soil pH, Ammonia Volatilization, and Nitrogen Use Efficiency

Nitrogen use efficiency is closely linked to soil pH. As pH rises above neutral, the equilibrium between NH₄⁺ and NH₃ shifts toward gaseous ammonia, increasing volatilization losses. This phenomenon explains why ammonium-based fertilizers often perform better in slightly acidic to neutral soils.

From a fertilizer management perspective, reducing volatilization is essential not only for economic reasons but also for minimizing nitrogen losses to the atmosphere. Proper placement, timing, and moisture management are therefore critical components of ammonium sulfate application strategies.

5. Practical Recommendations for pH-Based Fertilizer Management

To optimize ammonium sulfate fertilizer application across different soil conditions, the following best practices are recommended:

Conduct soil testing before each growing season to determine pH and nutrient status
Adjust application rates and timing based on crop growth stage and soil reaction
Avoid surface application on high-pH soils without incorporation or irrigation
Monitor long-term soil pH trends when ammonium sulfate is used regularly

This data-driven approach supports precision fertilization, helping growers achieve higher nutrient efficiency and sustainable yields.

6. Conclusion: Toward Precision Fertilization Based on Soil pH

Ammonium sulfate fertilizer remains a valuable tool in modern agriculture, but its effectiveness is highly dependent on soil pH conditions. By aligning fertilization strategies with soil chemistry, growers can maximize nitrogen and sulfur availability while minimizing losses and environmental impact.

Risso continues to support global partners with technically sound fertilizer solutions and agronomic insights, enabling more precise nutrient management across diverse soil environments.

7. Frequently Asked Questions (FAQs)

1. When is the best time to apply ammonium sulfate fertilizer?

Ammonium sulfate is best applied before planting or during early crop growth to meet nitrogen and sulfur demand and improve nutrient uptake efficiency.

2. Does ammonium sulfate lower soil pH?

Yes. Ammonium sulfate has an acidifying effect due to nitrification, making it suitable for neutral to alkaline soils but requiring caution in acidic soils.

3. What are the advantages of ammonium sulfate compared to other nitrogen fertilizers?

Ammonium sulfate supplies both nitrogen and sulfur, offers stable ammonium nitrogen, and improves micronutrient availability in high-pH soils.

4. Does long-term use of ammonium sulfate affect soil acidity?

Yes. Continuous use can gradually lower soil pH, so long-term programs should include regular soil pH monitoring and corrective practices.

5. Is ammonium sulfate effective for sulfur-deficient crops?

Yes. It provides readily available sulfate sulfur, making it effective for crops with high sulfur demand such as cereals, oilseeds, and cash crops.

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