Rising sulfur deficiencies have put sulfur in the spotlight in recent years, leading to increased use of the nutrient in agriculture. A Business Wire report estimates that by 2026, the sulfur fertilizer market will reach a value of $7.03 billion, up from just $4.52 billion in 2017.
As sulfur continues to gain importance in crop nutrition, sulfur fertilizer processing will continue to be at the forefront of development efforts.
Sulfur’s Role in Crop Production
As scientists are learning, each and every single nutrient, no matter how small the quantity required by the plant, is critical to maximizing plant growth and yield. As the fourth most utilized nutrient, sulfur is certainly no exception.
Sulfur contributes to plant growth in a wide range of ways, including assisting in seed production, promoting hardiness, aiding in chlorophyll formation, and more. It is also essential in nitrogen use efficiency. Therefore, a deficiency in sulfur is recognized as limiting to crop growth, yield, and quality.
Growing Sulfur Deficiency
Sulfur deficiencies have become more common in recent years, in large part, as a result of increasing regulations around emissions, particularly those targeting sulfur dioxide from the burning of fossil fuels.
Sulfur sources once deposited via acid rain caused by sulfur emissions have largely been mitigated. And although efforts to curb air pollution are a critical endeavor, the improvement has led to the atmosphere delivering less sulfur to soils, causing a decline in plant-available sources of this essential nutrient. Soils most prone to a sulfur deficiency are those that exhibit low organic matter, are sandy, or those that are more vulnerable to erosion.
According to USA Gypsum, the decline trend can also be attributed to newer crop varieties bred for higher yields, which extract more sulfur than older varieties. Excess phosphorus, which can displace sulfur, along with other soil conditions, are also to blame. Other contributing factors include reduced applications of manure and an increased use of high-analysis fertilizers.¹
Incorporating Sulfur into Fertilizers & Soil Amendments
Sulfur can be included in fertilizer and soil amendment products through a broad range of sources. Commonly utilized sources include:
Elemental Sulfur
Elemental sulfur can be applied as a stand-alone nutrient, but is not readily available to the plant, requiring time and favorable soil conditions to oxidize to plant-available sulfate (SO42-).
NPKS
Sulfur is now frequently incorporated into NPK fertilizer products, either as part of a bulk blend or in the formulation of a complex fertilizer.
Ammonium Sulfate
Once the nitrogen fertilizer of choice, ammonium sulfate is making a comeback as an excellent source of sulfur that also provides nitrogen.
Potassium Sulfate (K2SO4)
Potassium sulfate, also known as sulfate of potash, or SOP, provides potassium in addition to sulfur.
Langbeinite
Langbeinite, considered a potash fertilizer, is a mineral substance that provides potassium, magnesium, and sulfate in the form of K2Mg2(SO4)3.
Phosphoric Fertilizers
Many companies are now also incorporating elemental sulfur into phosphoric fertilizers such as MAP, DAP, TSP, and SSP to provide an effective and economic fertilizer option.
Organic matter
Sources of organic matter such as manure can greatly influence the amount of plant-available sulfur in soils.
Gypsum
Gypsum, or calcium sulfate dihydrate, is another common source of sulfur. In addition to sulfur, gypsum also provides calcium. Both natural and synthetic (FGD) gypsum are widely used in agriculture. Synthetic (FGD) gypsum is the sulfur removed from emissions at fossil fuel-fired power plants that previously resulted in acid rain. The use of synthetic gypsum offers a controlled approach to sulfur addition with the added benefit of diverting a process by-product from landfill and reducing the need to mine natural gypsum resources. Gypsum products, whether natural or synthetic in origin, are typically pelletized prior to use.
Coating Sulfur
A main concern in developing a sulfur fertilizer or soil amendment product is ensuring a controlled release rate. This is the case with both elemental sulfur and plant-available sulfates and is addressed through coating, with the best results typically provided by a coating drum. It is worth noting that molten elemental sulfur is also used as a coating itself in some cases to add sulfur to existing fertilizers.
Coating Elemental Sulfur
Elemental sulfur is not water soluble. As a result, the oxidation required to convert elemental sulfur to a plant-available sulfate creates a naturally slow release rate. While this may be beneficial in the long term, it does not provide immediate results. Depending on the soil conditions, the oxidation timeline can be significant.
To speed up the conversion to sulfate, elemental sulfur can be combined with other materials (typically via pelletizing) to help increase water penetration into the granule and promote oxidation.
Coating Sulfates
In contrast to elemental sulfur, sulfates are water soluble, and are subsequently more available to the plant, but at a greater risk of leaching. Leaching can cause sulfur to move away from the roots before they have a chance to absorb it, ultimately producing nutrient runoff and not providing the intended benefit.
To prevent this, sulfates can be coated to promote a slower release of the nutrient into the soil. In this case, a variety of coatings may be used depending on the objective.
Coating has generally become more common practice in the industry as producers look to develop specialty fertilizers.
Process Development for Sulfur Fertilizer Integration
As with any novel product, testing is a critical aspect of designing a successful commercial-scale production line.
As a key resource in granular fertilizer production, FEECO has worked with the industry’s leading companies to bring sulfur back to the market in the form of premium fertilizer and soil amendment products. From ammonium sulfate to langbeinite, FEECO can provide comprehensive testing services to develop a commercial-scale production line that consistently producers product of the desired specifications.
A wide range of equipment is available in the FEECO Innovation Center, allowing products to be tested at batch and continuous pilot scale. With extensive experience in both traditional and specialty fertilizer production, process engineers are equipped with the knowledge and tools needed to develop or optimize a production line that meets its intended goal.
Please note that FEECO does not work with molten sulfur unless it is pre-ground.
Conclusion
Sulfur is a necessary nutrient in the growth and yield of healthy crops. Given the increasing trend of sulfur deficiencies, the provision of it as a fertilizer or soil amendment is critical, with many options available.
As a pioneer in fertilizer production and pelletizing, FEECO is the preferred industry resource for comprehensive testing services, process and product development, custom production equipment, and parts and service support.
For more information on our capabilities, contact us today!