By Dr. Wes Chun Ph.D. 
Grower's Secret, Chief Science Officer Emeritus

View Details

April 4,

Introduction
Supplying micronutrients to plants can be problematic. Many N, P, or K agricultural fertilizers lack sufficient quantities of essential micronutrients to meet plant needs. Micronutrients are often applied pre-plant but additional in season applications may be needed to address plant micronutrient deficiencies that may occur due to high or low soil pH, plant or environmental issues. Synthetic micronutrient fertilizers in the ionic form are available to plants within a limited pH range (pH 6.5 to 7.5).  High soil pH (pH>7.5) decreases the availability of copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn). When the soil pH is low, the macronutrients calcium (Ca),  magnesium (Mg), and molybdenum (Mo) may be limited. Thus, soil applications of synthetic micronutrients are particularly challenging and can be more problematic especially in sandy soils or when growing crops that have high micronutrient demands. Synthetic and organic chelated micronutrients were developed that are less reactive to soil conditions. These fertilizers can significantly enhance nutrient uptake and improve efficiency of utilization.  Application rates of most chelated micronutrients are 0.2 to 1 pound per acre for vegetables, and 0.1 to 0.5 pound per acre for fruits.  Foliar application is often more effective.

What are Chelated Micronutrients?
Chelated micronutrients are fertilizers where the micronutrient ion (for example Fe or iron) is surrounded by a larger molecule called a ligand or chelator. Ligands can be natural or synthetic chemicals.  These compounds combined with a micronutrient forms a chelated micronutrient. Chelated micronutrients are protected from oxidation, precipitation, and immobilization in certain conditions. A few examples of ligands are in Table 1. These chelates have different effective pH ranges.  The effective pH range for Fe-EDTA is 4 to 6.5, Fe-DTPA is 4 to 7.5, and Fe-EDDHA is 4 to 9.  Fe-EDDTA is effective when pH is greater than 7 but it is costlier. There are also many naturally occurring chelating agents such as amino acids, organic acids, humic and fluvic acids, ligninosulfonates, ligninipolycarboxylates, sugar acids, phenols, polyphosphates, flavonoids, and siderophores. These are generally less expensive, functional over a wider pH range, and less toxic to plants.  Both synthetic and non-synthetic chelates are OMRI permitted.

Are Chelated Micronutrients Needed?
Soil is heterogenous and complex and applied traditional micronutrients may become unavailable to the plant because of oxidation or precipitation. Use of chelated micronutrients improves the bioavailability of micronutrients and can contribute to crop quality and yield. Chelated micronutrients should be considered if plants display micronutrient stress, in alkaline soils that limit micronutrient availability, or when soil micronutrient supplementation is insufficient.

Where am I Least Likely to Need Chelated Micronutrients? 
Soil that has igneous parent material or other rocks high in nutrients can supply the necessary micronutrients. Some igneous rocks are high in zinc. Clay soils with high Cation Exchange Capacity (CEC) or micronutrients in the mineral structure may not need additional micronutrients. High CEC soils can “capture” micronutrients and maintain them in ionic form for the plants. Micronutrients in the mineral structure are released over time.  Soils with high organic matter also tends to maintain micronutrients in bioavailable form.

Where am I Most Likely to Need Chelated Micronutrients?
US and Canadian soils may be deficient in boron (B). Boron is not influenced by organic matter, leaches easily, and can be locked up by fresh lime. Boron is higher in alluvial than igneous soils. It is low in subsoils and dry weather may create boron deficiency symptoms when plant roots go deeper in search of water.

The type of soil can affect micronutrient availability. Leached sandy soils have low CEC are low in B, Cu, Mn, Mo, and Zn. Quartz is low in Zn. Alluvial soils, weathered acid soils that are subject to leaching, and low organic matter soils all tend to be deficient in micronutrients. High pH soils are low in Fe, Mn, Zn.  Acidic soil may be deficient in Mo.

Does my Crop Need Chelated Micronutrients?
The answer is an obvious yes if you are seeing micronutrient deficiency symptoms in your crop. The good news is that foliar application of a micronutrient can usually remediate the problem in a few days.  You should consider additional micronutrients if you are growing a particularly susceptible crop such as citrus which is susceptible to low levels of Cu, Fe, Mn, and Zn and especially if the soil is alkaline. (See Table 2 for a list of vegetables and fruits, and their susceptibilities to micronutrient deficiencies).

It is important to address micronutrient deficiencies especially in crops that are highly susceptible. In these instances, significant improvement can be obtained in crop quality and yields. In situations where no micronutrient deficiency exists, application of additional micronutrients may have some value. For example, total yield in pear was higher (but not statistically significant) with amino acid chelated Fe compared to controls and ranged from 7 to 64% increase between years of the study. Shoot length increased and there were no changes in fruit firmness. In other crops, Fe and Zn content in leaves were higher when Fe and Zn chelates were used. Since amino acid chelated micronutrients are relatively new to the market, additional research is needed to determine if there are consistent benefits for additional micronutrient supplementation.

Take-Home Message

• High pH soil often has low bioavailability in micronutrients such Cu, Fe, Mn, and Zn.
• Crop susceptibility to micronutrient deficiencies depends on the plant species and cultivar, and environmental conditions.
• Inorganic water-soluble micronutrient soil application is often ineffective for correcting micronutrient disorders (foliar application is recommended).
• Chelated micronutrients are less reactive to soil conditions and can enhance nutrient uptake and utilization.

Note:  Check with your local recommendations and regulations as some states require documentation of a micronutrient deficiency before use of these types of products.

Sulfate vs Chelated Fertilizers: Key Differences and Garden Benefits Explained

Written by makenzi logan

• 

Posted on October 11

Choosing the right fertilizer is a challenging but essential aspect for maintaining a healthy, thriving garden. With so many options available, it can be difficult to determine the best choice for your plants. Two popular types of fertilizers, sulfate and chelated, offer distinct benefits based on soil type, plant needs, and environmental conditions. Understanding the key differences between these two fertilizers can help you make informed decisions that maximize plant growth and nutrient absorption. In this article, we will explore how sulfate and chelated fertilizers are produced, their unique properties, and when to use each to ensure your garden flourishes year-round. Selecting the right fertilizer for your garden can be challenging. To determine which product will best nourish your plants, it's essential to understand the different types and their properties. Consider the following questions to guide your decision:

• What are chelated fertilizers, and how are they produced?
• What are sulfate fertilizers, and how are they produced?
• What are the key differences between sulfate and chelated fertilizers?
• How do sulfate and chelated fertilizers differ in terms of nutrient release?
• Why are chelated fertilizers more effective in a wider range of pH levels than sulfate fertilizers?
• How do sulfate and chelated fertilizers compare in terms of cost?
• What are the main benefits of sulfate vs chelated fertilizers?
• Which plants benefit the most from sulfate vs chelated fertilizers?
• What are the environmental impacts of sulfate and chelated fertilizers?
• How do you choose between sulfate and chelated fertilizers for your garden?

What are Chelated Fertilizers and How Are They Produced?

Chelated fertilizers are specialized formulations containing micronutrients bound to organic molecules called chelating agents. This binding process stabilizes the micronutrients, making them more available to plants over a wide range of soil conditions.

Production of Chelated Fertilizers: Chelated fertilizers are produced through a controlled chemical process in which micronutrients such as iron, zinc, or manganese are combined with chelating agents like EDTA, DTPA, or EDDHA. The chelating agent "wraps" around the micronutrient, preventing it from reacting with other elements in the soil and becoming unavailable to plants.

Examples: Chelated fertilizers offer various micronutrients in stable forms. These nutrients are commonly bound to chelating agents, making them more accessible to plants across a wider range of soil conditions. Some popular chelating agents and their benefits include:

• EDTA (Ethylene Diamine Tetraacetic Acid): Commonly used for chelating iron, zinc, copper, and manganese, making these nutrients available even in challenging soil conditions.

• DTPA (Diethylenetriamine Pentaacetic Acid): Particularly effective for iron availability in slightly alkaline soils and is also used for zinc and manganese chelation.

Essential micronutrients such as iron, zinc, copper, and manganese are delivered by chelated fertilizers in plant-available forms, ensuring absorption even in difficult soil conditions. Some of the most effective chelating agents include:

• Chelated Iron EDTA: Ideal for maintaining iron availability in a wide range of soils, ensuring plants receive sufficient iron for healthy growth.

• Chelated Iron DTPA: Particularly effective in slightly alkaline soils, this chelated form of iron remains available to plants without becoming locked up in the soil.

• Chelated Manganese EDTA: Provides manganese in a highly available form, promoting healthy photosynthesis and enzyme function in plants.

• Chelated Zinc EDTA: Helps prevent zinc deficiencies, particularly in calcareous soils, supporting healthy plant growth and development.

• Chelated Copper EDTA: Ensures copper remains available to plants, improving lignin formation and plant resilience.

What are Sulfate Fertilizers and How Are They Produced?

Sulfate fertilizers are a type of fertilizer that deliver essential nutrients to plants in the form of sulfate ions (SO₄²⁻). These ions provide sulfur, an important nutrient for plant growth, as well as other essential nutrients like potassium and magnesium, depending on the specific formulation. Sulfate fertilizers are highly soluble in water, allowing plants to readily absorb the nutrients they provide.

Production of Sulfate Fertilizers: The production of sulfate fertilizers involves various industrial processes depending on the nutrients they contain. One common method involves combining sulfuric acid with other elements or compounds to form sulfate-based products. These reactions produce fertilizers that are effective in providing nutrients quickly to plants. Some sulfate fertilizers are also derived as byproducts of other industrial activities, making them widely available for agricultural use. The manufacturing process is designed to ensure the final product is stable, soluble, and ready for plant uptake, providing immediate benefits when applied to soils.

Examples: Sulfate fertilizers provide essential nutrients like iron, zinc, copper, manganese, magnesium, and nitrogen in sulfate forms, which plants can readily absorb. These nutrients are critical for various plant functions and growth processes.

• Ferrous Sulfate: Supplies iron in a soluble form, essential for chlorophyll production and preventing iron deficiencies, particularly in acidic soils.
• Zinc Sulfate: Delivers zinc to plants, promoting enzyme function and protein synthesis, and is especially effective for correcting zinc deficiencies in various crops.
• Manganese Sulfate: Provides manganese, which is vital for photosynthesis and the activation of enzymes involved in plant metabolism.
• Copper Sulfate: Ensures plants receive copper, necessary for lignin formation, enzyme activation, and overall plant resilience.
• Ammonium Sulfate: Supplies both nitrogen and sulfur, aiding in protein synthesis and improving the overall health of crops, especially in sulfur-deficient soils.
• Magnesium Sulfate (Epsom Salt): Provides magnesium, a key component of chlorophyll, and sulfur, both of which are critical for healthy plant growth and enzyme activity.

Four Key Differences Between Sulfate and Chelated Fertilizers

When comparing sulfate and chelated fertilizers, it is important to consider their differences in chemical composition, nutrient availability, pH range effectiveness, and soil interaction.

1. Chemical Composition

• Sulfate fertilizers contain nutrients in their ionic forms (e.g., SO₄²⁻), which dissolve easily in water and are immediately available to plants.
• Chelated fertilizers bind nutrients to chelating agents, which protect the nutrients from soil reactions and make them available to plants over time.

2. Nutrient Availability

• Sulfate fertilizers provide a quick nutrient release but can be prone to leaching in sandy soils.
• Chelate fertilizers offer a controlled release, providing nutrients steadily over time, reducing the risk of leaching.

3. pH Range Effectiveness

• Sulfate fertilizers work best in acidic to neutral soils but may become ineffective in highly alkaline conditions due to nutrient precipitation.
• Chelated fertilizers are highly effective across a wide pH range, especially in alkaline soils, where they prevent micronutrient lock-up.

4. Interaction with Soil

• Sulfates can acidify the soil over time, which may benefit some plants but harm others.
• Chelates have little to no impact on soil pH and remain effective even in soils with challenging conditions.

Chelated vs. Traditional (sulfate) Fertilizers: Why and how do They Work in Diverse soil pH levels?

Let’s dive deeper into one of the most important key differences between the two types of fertilizer, pH effectiveness. Chelated fertilizers have gained popularity among gardeners and farmers for their versatility across various soil conditions especially in a wide range of pH levels. Let's explore why these fertilizers maintain their effectiveness in a broad spectrum of pH levels.

1. The Chemistry Behind Chelated Fertilizers

• Definition: Chelated fertilizers contain nutrients bound to organic molecules called chelates.
• Structure: The word "chelate" comes from the Greek word "chele," meaning claw, describing how the molecule surrounds the nutrient.
• Common Chelating Agents: EDTA, DTPA, and EDDHA are frequently used in agricultural applications.

2. How Soil pH Affects Nutrient Availability

• pH Scale: Soil pH typically ranges from 4.0 (very acidic) to 8.5 (very alkaline).
• Nutrient Solubility: Different nutrients become more or less available at various pH levels.
• Micronutrient Challenges: Iron, manganese, and zinc are often less available in alkaline soils.

3. Chelated Fertilizers vs. Traditional Fertilizers in Different pH Environments

pH Level

Traditional Fertilizers

Chelated Fertilizers

Acidic (< 6.5)

Generally effective

Effective

Neutral (6.5-7.5)

Effective

Highly effective

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Alkaline (> 7.5)

Less effective

Remain effective

4. Mechanisms of pH Tolerance in Chelated Fertilizers

• Protective Shield: Chelates form a protective barrier around nutrients, shielding them from soil reactions.
• Prevents Precipitation: The chelate structure keeps nutrients soluble, even in alkaline conditions where they might otherwise form insoluble compounds.
• Controlled Release: Chelates slowly release nutrients, maintaining availability over time regardless of pH fluctuations.

5. Benefits of pH-Tolerant Chelated Fertilizers

• Versatility: Effective in a wide range of soil types and conditions.
• Reduced Waste: Less nutrient loss through fixation or leaching.
• Improved Nutrient Uptake: Plants can more easily absorb chelated nutrients.
• Cost-Effective: Despite higher initial costs, chelated fertilizers can be more economical due to increased efficiency.

6. Choosing the Right Chelated Fertilizer for Your pH Needs

• EDTA Chelates: Effective up to pH 6.5
• DTPA Chelates: Suitable for soils with pH up to 7.5
• EDDHA Chelates: Remain stable even in highly alkaline soils (pH > 7.5)

Chelated vs Sulfate Fertilizers: How Do They Release Nutrients Differently?

Another key in  exploring how these two types of fertilizers work to nourish your plants is understanding the nutrient release mechanisms of chelated and sulfate fertilizers is crucial for effective plant nutrition. To understand how each fertilizer works, it’s helpful to examine how they release nutrients into the soil and how that affects plant nutrition.

1. Sulfate Fertilizers: Rapid Nutrient Release

• Dissolution Process: Sulfate fertilizers dissolve quickly in water, releasing nutrients in their ionic form (e.g., SO₄²⁻).
• Immediate Availability: Plants can uptake these dissolved nutrients rapidly, providing a quick nutritional boost.
• Leaching Risk: In sandy soils, the fast release can lead to nutrient leaching, potentially reducing long-term effectiveness.
• pH Sensitivity: Sulfates work best in acidic to neutral soils but may become less effective in highly alkaline conditions.

2. Chelated Fertilizers: Controlled Nutrient Release

• Chelation Process: Nutrients are bound to organic molecules called chelates, forming a protective structure.
• Gradual Availability: The chelate structure releases nutrients slowly over time, ensuring a steady supply to plants.
• Reduced Leaching: The controlled release minimizes nutrient loss through leaching, especially in sandy soils.
• pH Tolerance: Chelated nutrients remain available across a wide pH range, making them effective even in challenging soil conditions.

3. Comparing Nutrient Release Patterns

Aspect

Sulfate Fertilizers

Chelated Fertilizers

Release Speed

Fast

Slow and controlled

Nutrient Availability

Immediate

Prolonged

Risk of Leaching

Higher

Lower

pH Sensitivity

More sensitive

Less sensitive

4. Factors Affecting Nutrient Release

• Soil Texture: Sandy soils may accelerate sulfate nutrient release, while clay soils can slow it down.
• Temperature: Warmer temperatures generally increase the release rate for both types.
• Moisture: Adequate soil moisture is essential for the dissolution of sulfates and the functioning of chelates.
• Microbial Activity: Soil microbes can influence the breakdown of chelates, affecting nutrient release.

5. Choosing the Right Fertilizer for Your Needs

• Quick Results: Opt for sulfate fertilizers when rapid nutrient uptake is needed.
• Long-Term Nutrition: Choose chelated fertilizers for sustained nutrient release over time.
• Soil pH Challenges: In alkaline soils, chelated fertilizers often perform better.
• Environmental Concerns: Chelated fertilizers may be preferable in areas prone to nutrient runoff.

Cost Comparison: Sulfate vs. Chelated Fertilizers

There are plenty of technical reasons to consider when deciding between chelated and sulfate fertilizers, but cost is another important factor that can influence your decision. Chelated fertilizers tend to have a higher upfront price due to the more complex manufacturing process, while sulfate fertilizers are generally more affordable. However, the long-term cost efficiency can vary depending on your soil type and the needs of your plants.

Upfront Cost: Chelated fertilizers are typically more expensive upfront due to the complexity of their production.

Cost Efficiency in Different Soil Types: Chelated fertilizers may be more cost-effective in alkaline soils, where sulfate-based fertilizers can become ineffective.

Application Frequency and Longevity: Sulfate fertilizers may require more frequent applications due to their quick-release nature, while chelated fertilizers often need fewer applications due to their slow-release properties.

Comparing the Benefits: Sulfate vs. Chelated Fertilizers for Garden Success

Sulfate fertilizers offer several key benefits that make them highly effective for a variety of plants and soil conditions:

• Immediate nutrient availability: Sulfate fertilizers dissolve quickly in soil, allowing plants to absorb nutrients immediately. This fast action is particularly helpful for plants that show signs of nutrient deficiencies and need rapid recovery.
• Ideal for acid-loving plants: These fertilizers slightly acidify the soil, creating a favorable environment for acid-loving plants like blueberries, azaleas, and hydrangeas.
• More affordable upfront: Sulfate fertilizers are generally more cost-effective compared to other types, making them an accessible choice for gardeners who want to provide essential nutrients without high initial costs.

Chelated fertilizers, in contrast, provide their own set of unique benefits, particularly in challenging soil conditions:

• Effective in a wide range of pH conditions: Chelated fertilizers are stable in both acidic and alkaline soils, preventing nutrient lock-up and ensuring that plants can absorb essential micronutrients, even in difficult conditions.
• Controlled release reduces the risk of nutrient loss: Chelates release nutrients gradually, minimizing the chances of leaching and ensuring a consistent supply of nutrients to plants over time.
• Essential for micronutrient deficiencies: Chelated fertilizers are crucial for addressing deficiencies of important micronutrients like iron, zinc, and manganese, particularly in soils where these nutrients are not readily available in their natural forms.

Which plants benefit the most from sulfate vs chelated fertilizers?

Plants That Benefit from Sulfate Fertilizers

• Sulfur-loving plants: cruciferous vegetables, legumes, onions, and garlic.

• Grasses: turfgrass and pasture grasses.

• Root crops: potatoes.

• Fruit trees: citrus, apples, peaches, and cherries.

Plants That Benefit from Chelated Fertilizers

• Iron-loving plants: citrus trees, fruit trees, blueberries, tomatoes, and peppers.

• Zinc and manganese-loving plants: corn, legumes, and grapes.

Environmental Impact of Chelated and Sulfate Fertilizers

Chelates

Chelated fertilizers, while highly effective at delivering essential micronutrients to plants, come with certain environmental considerations. One potential issue is the risk of nutrient runoff, especially if chelates are over-applied. When this occurs, excess nutrients can enter nearby water sources, contributing to water pollution. Additionally, some chelating agents, such as EDTA, are not biodegradable. This means that they can persist in the environment for long periods, potentially causing long-term ecological impacts. The persistence of these synthetic chelating agents raises concerns about their accumulation in soil and water systems, potentially mobilizing heavy metals or other contaminants.

Sulfates

Sulfate fertilizers, on the other hand, also present environmental challenges, particularly in terms of their effect on soil chemistry. Over time, the regular use of sulfate-based fertilizers can lead to soil acidification. This can be beneficial for certain acid-loving plants but harmful to others, potentially upsetting the balance of the soil ecosystem. Additionally, sulfate fertilizers, like their chelated counterparts, are susceptible to leaching, especially in sandy or well-drained soils. When leaching occurs, essential nutrients may be washed away, entering groundwater or nearby bodies of water. This can lead to nutrient contamination and contribute to the problem of eutrophication, where excessive nutrient levels in water bodies promote harmful algal blooms that deplete oxygen levels and disrupt aquatic life.

How to Choose Between Sulfate and Chelated Fertilizers

When deciding whether to use sulfate or chelated fertilizers, several factors should guide your choice, including soil type, plant needs, nutrient deficiencies, and environmental conditions. Here's how each example can help you determine the right option for your garden:

• Acidic Soils: In soils with a low pH (acidic conditions), sulfate fertilizers are typically more effective. The acidic environment enhances the solubility of sulfate-based nutrients like ferrous sulfate, ammonium sulfate, and manganese sulfate, making them easily available for plant uptake. For instance, if your plants show signs of iron or sulfur deficiency in acidic soils, using ferrous sulfate or ammonium sulfate would be ideal because they release nutrients rapidly and are highly effective in these conditions.
• Alkaline Soils: In soils with a high pH (alkaline conditions), chelated fertilizers tend to perform better. This is because, in alkaline soils, micronutrients like iron, zinc, and manganese often become locked up or precipitate out, rendering them unavailable to plants. Chelates, such as Chelated Iron EDTA or Chelated Zinc EDTA, prevent this nutrient lock-up by protecting the nutrient in a stable, soluble form, allowing plants to absorb them efficiently. If your garden is in an area with alkaline soil and you're seeing symptoms of micronutrient deficiencies, chelated fertilizers are the best choice to ensure sustained nutrient availability.
• Sandy or Well-Drained Soils: In soils with high drainage, sulfate fertilizers can be prone to leaching, especially if the nutrients are applied in excess. In these conditions, using chelated fertilizers can offer a more controlled release of micronutrients, minimizing nutrient loss and providing plants with a steady supply over time. For example, Chelated Manganese EDTA or Chelated Copper EDTA would be ideal for long-term nutrient availability in sandy soils.
• Micronutrient Deficiencies: The type of deficiency you're addressing can also determine whether a sulfate or chelate is more appropriate. For instance, if a soil test shows low levels of copper or zinc, and your soil is neutral to slightly acidic, using zinc sulfate or copper sulfate can quickly address these deficiencies. However, in more alkaline soils, Chelated Zinc EDTA or Chelated Copper EDTA would be a better option to prevent nutrient lock-up and ensure effective absorption.
• Plant Type: Certain plants, especially those prone to iron or zinc deficiencies (like citrus, tomatoes, and peppers), may benefit more from chelated fertilizers, particularly in challenging soil conditions. On the other hand, sulfur-loving crops, such as cruciferous vegetables, legumes, and onions, often respond better to sulfate fertilizers, like ammonium sulfate or magnesium sulfate, which provide both sulfur and other essential nutrients.

By evaluating your soil type, drainage, nutrient deficiencies, and the specific needs of your plants, you can make an informed choice between sulfate and chelated fertilizers to optimize your garden’s health.

Conclusion

Choosing between sulfate and chelated fertilizers depends on your soil's pH, the plants you're growing, and your environmental goals. Sulfates offer quick results and work well in acidic soils, while chelates provide long-term nutrient availability and excel in challenging soil conditions. By understanding the key differences, you can make an informed choice for a thriving garden. For all of your sulfate and chelated fertilizer needs, you can explore high-quality options at Greenway Biotech, where you’ll find a wide range of products such as organic and water soluble fertilizers tailored to meet your gardening requirements.

Contact us to discuss your requirements of chelated micronutrient fertilizer. Our experienced sales team can help you identify the options that best suit your needs.