Fertilizer International 513 Mar-Apr 2023
31 March 2023
Delivering sulphur nutrition
PRODUCTS & PROCESSES
Delivering sulphur nutrition
Sulphur is a vital secondary crop nutrient. It can be delivered in sulphate, thiosulphate and elemental form. The range of product and process options are outlined.
Increasing agricultural value
Sulphur is becoming an increasingly important crop nutrient due to three main factors (Fertilizer International 497, p24):
- Falling atmospheric deposition. Soil sulphur deficiency, a relative rarity 20 years ago, is becoming more common. The deposition of sulphur dioxide emissions from the atmosphere used to guarantee that soils in many regions were automatically enriched and replenished with sulphur. This is no longer the case as increasingly stringent environmental regulations and the introduction of low-sulphur fuels have sharply cut emissions.
- The prevalence of high-analysis fertilizers. Farmers are continuing to switch to high-analysis products, containing little or no sulphur, at the expense of sulphur-rich, lower analysis products. This long-term buying trend has also put sulphur replenishment on a downward path.
- Rising cropping intensity. Improving crop yields are withdrawing ever larger amounts of sulphur from the field.
These three factors are, however, opening up opportunities for fertilizer producers. A number of leading manufacturers are capitalising on the value of sulphur by broadening their portfolios and supplying sulphur-enhanced fertilizers as premium products to meet growing market demand. New processes to coat fertilizers with sulphur, or disperse sulphur within fertilizer granules, are also being developed and commercialised.
Product and process innovation
AgriTech company Sulvaris manufactures innovative sulphur-containing fertilizers for sustainable and regenerative agriculture. The Calgary-headquartered company has commercialised its micronised sulphur technology (MST® ). This economically micronises elemental sulphur to an average size of less than 10 microns. In collaboration with Nutrien, the world’s largest fertilizer producer and retailer, Sulvaris has incorporated this enhanced efficiency technology within mono-ammonium phosphate (MAP) to create a MAP + MST® product. This is marketed by Nutrien under the brand name SmartNutritien™ .
Sulvaris has also created a patented urea + MST® product. This is manufactured by incorporating micronised elemental sulphur directly into the urea melt during the granulation process. Urea + MST® can produce granules with a 5-12 percent elemental sulphur content.
Sulphur is evenly dispersed throughout the granule and therefore provides maximum soil-to-fertilizer contact. The presence of tiny micron-size particles also increases surface area dramatically. This speeds up the microbial oxidation needed to convert insoluble elemental sulphur into soluble plant-available sulphate.
Unlike elemental sulphur products made up of larger sized particles, which may not fully oxidise during the application season, MST® begins to oxidise within days of application and provides the crop with season-long sulphur nutrition. MST® can also be co-granulated with a variety of other N, P, K and sulphate fertilizers. MST® offers the following advantages: l It can be mass produced economically and safely in a single step via a low temperature and pressure process
AGRICULTURAL CONSUMPTION OF SULPHUR
Global agricultural consumption of sulphur is around 13.3 million tonnes (Figure 1), according to a first-of-its-kind assessment by the International Fertilizer Association (IFA). This volume is much higher than the frequently quoted estimate of 10-11 million tonnes. However, this latest tonnage is probably still an underestimate, suggests IFA, as it excludes data for some NPK+S products1 .
The sulphur fertilizer market divides into two main categories – traditional sulphate fertilizers and sulphur-enhanced fertilizers. These have a wide range of nutrient compositions. Liquid sulphur products – thiosulphates – are also favoured in some countries and regions, particularly in North America and Europe.
Sulphate fertilizers
Traditional sulphate fertilizers have long dominated global demand (Fertilizer International 476, p19). They include:
- Single superphosphate (SSP). The second largest-selling phosphate fertilizer on the market after diammonium phosphate (DAP). Consumption is concentrated in four main markets, China, Brazil, India and Australia, which collectively account for around 85 percent of total global demand.
- Ammonium sulphate (AS). Consumption is on the rise even though its nitrogen content is much lower than urea and ammonium nitrate. World supply (26.4 million tonnes) has been boosted by the massive growth of ‘involuntary’ production capacity in China. The use of AS in NPK blends has become increasingly popular as awareness of sulphur deficiency in soils has become more widespread.
- Sulphate of potash (SOP). This is valued as a chloride-free source of potash for lucrative cash crops such as tobacco, tree nuts and citrus fruits. Agricultural consumption is 7-8 million tonnes currently. China accounts for more than half of global use. North America and Europe also offer sizeable markets Global demand is supply-constrained meaning that SOP trades at a premium.
- Sulphate of potash magnesia (SOPM). The market for SOPM, similar to SOP and SSP, is highly concentrated with just four countries, China, the US, Canada and Germany, accounting for the lion’s share of consumption. Global demand has grown strongly in recent years.
- Ammonium phosphate sulphate (APS). This is a commonly produced grade of NP+S fertilizer (16-20-0-14S) with a 60 percent ammonium sulphate and 40 percent monoammonium phosphate (MAP) composition. It is directly applied to forage crops in many countries, particularly legumes, and is also a popular choice of fertilizer for small grains and oilseed rape (canola).
Overall, the global sulphur fertilizer market is still dominated by AS, SSP and SOP, with these three products combined being responsible for 70 percent of agricultural sulphur consumption (Figure 1).
Sulphur-enhanced fertilizers
Global crop requirements for sulphur are rising and are thought to exceed 24 million tonnes, a volume far in excess of current consumption levels. Fertilizer producers have reacted to this widening demand gap by developing sulphur-enhanced fertilizers. Many of these premium products are manufactured by incorporating elemental sulphur into high analysis fertilizers, either within granules or as an external coating.
Introducing a liquid sulphur spray to urea, TSP, MAP or DAP during drum or pan granulation, for example, results in NPS products with a 5-20 percent elemental sulphur content. Sulphur-enhanced fertilizers combine nutrient availability with high use-efficiency, and also have good storage and handling properties. Examples include:
- Sulphur-bentonite
- Sulphur-coated urea, MAP or TSP
- Sulphur-enriched SSP
- Sulphur-enhanced MAP enriched with sulphate.
- It can be incorporated directly into the urea melt pipeline for granulation or prilling
- The process has low capex and opex costs, by avoiding expensive modifications and production losses at the urea plant, and produces excellent quality products.
Shell Sulphur Solutions developed the successful and pioneering micronised sulphur product Thiogro, which it licenses to key fertilizer producers around the world. The company successfully commercialised and patented technology for incorporating sulphur into ammonium phosphates in the early 2000s. Sulphur-enhanced phosphate lines have subsequently been licensed and installed at fertilizer plants in Asia, North America and Australia. This include a major collaboration with SinoChem in China (Sulphur 381, p24).
Shell also landed a major licensing deal with OCP Group in 2016. This allows the Moroccan phosphate giant to produce its own range of highly-concentrated sulphur-enhanced fertilizers by using Thiogro technology to incorporate elemental sulphur into ammonium phosphates, NPKs and other products manufactured at its Jorf Lasfar site. By adding new and potentially highly-lucrative premium products to its existing fertilizer range, the licencing deal with Shell is an important long-term strategic move by OCP.
A more recent breakthrough was Shell’s development of Urea-ES (enhanced sulphur), a dispersion of micronised sulphur in urea. This innovative technology – introduced to the market by Shell in 2016 – suspends 7-20 percent elemental sulphur in a urea matrix with a nitrogen content of 43-37 percent.
Shell subsequently introduced Special-S, a further refinement of the technology, in 2017. This produces a co-granulated high sulphur content (11-0-0-75ES) urea product (Fertilizer International 492, p44). Shell has successfully collaborated with both thyssenkrupp Fertilizer Technology (Fertilizer International 510, p17) and IPCO, leading providers of fluid bed granulation and Rotoform finishing technology, respectively.
These partnerships mean Urea-ES and Special-S technologies are now widely available to producers wishing to expand their portfolios to include sulphur-enhanced fertilizers. H Sulphur Corp, one of Asia’s leading sulphur suppliers and sulphur-bentonite producers, has licensed Shell’s Special-S technology, commissioning the first ever production plant in South Korea. H Sulphur subsequently begun manufacturing and selling Special-S under its own Super S brand name. This product has been successfully sold and shipped to customers in Canada, Australia and Brazil (Fertilizer International 492, p44).
An innovative bi fluidised drum granulation (BFDG) process developed by Italy’s Ballestra is capable of coating urea using a wide variety of seeding materials in combination with a urea melt. This includes sulphur-coated urea production, according to Ballestra.
BFDG produces spherical granules by spraying a molten salt, suspension or clear solution onto seeds or recycled product. The process combines together drum granulation and fluidised bed technology as follows:
- The drum granulator consists of a cylindrical drum rotating around its axis equipped with lifters
- A fluidised bed installed inside the granulator is supplied with atmospheric/hot/cold and recycled air
- The BFDG also incorporates unique bi-fluid spraying nozzles that are able to generate granules with fine and coarse surfaces.
Essentially, the BFDG unit is a rotating drum with a fixed table inside made of a perforated metal sheet (Figure 2). The rotation of the drum lifts the granules onto the table, where they are kept in fluid bed conditions by air flowing through holes in the metal sheet. The perforated table is slightly inclined to one side. This allows dry granules from the fluid bed to fall back to the lower part of the rotating drum. While doing so, they pass through an incoming spray of fresh urea, which creates a further layer of material.
The North American market for The Mosaic Company’s successful and pioneering sulphur-enhanced MAP product range, MicroEssentials, broke through the one million t/a barrier at the end of 2013. Mosaic’s sales of 7.7 million tonnes of finished phosphates in 2021 included 3.8 million tonnes of MicroEssentials speciality products (and feed ingredients).
These versatile premium fertilizers are now applied to more than 10 percent of US farmland. They are suitable for both direct application and bulk blending and their increasing use is backed by more than a decade of field data and over 1,200 crop trials globally.
The proprietary Fusion process used in the manufacture of MicroEssentials joins together nitrogen, phosphorus, sulphur and zinc to create a nutritionally-balanced granule capable of boosting crop yields by 3-7 percent, compared to conventional MAP or DAP. Three main formulations are offered by Mosaic, all of these containing a 50:50 mix of elemental sulphur and sulphate.
Sulphur Mills Limited (SML) is the world’s largest manufacturer of water-dispersible granules (WDGs). The Mumbai-based company has been expanding rapidly and increasing the availability of these innovative sulphur-based products across the globe.
WDGs are extremely fine granules (2-4 micron size) manufactured by SML using a patented process. SML’s flagship products, Techno-S® and Techno-Z® , are the world’s first low-dose WDG fertilizers. They represent a technological leap forward in soil-based fertilizer applications, according to the company, and are helping to change the way sulphur-based fertilizers are perceived.
Both products have excellent water dispersion properties and are offered as either standalone sulphur microgranules (Techno-S® ) or zinc-fortified microgranules (Techno-Z® ). Techno-S® is a 90 percent sulphur fertilizer, while Techno-Z® combines 15 percent zinc with 70 percent sulphur.
Both fertilizers function at very low dosages and offer high nutrient use efficiency. They undergo quick oxidation, making S and Zn readily available to the plant throughout the season from early crop stages onwards.
SML has thoroughly tested WDGs agronomically – across countries, crop types and on different soil types. This has demonstrated their ability to improve various crop growth and quality parameters, including:
- Better crop yields
- Improved protein and oil content in oil seed crops
- Higher starch content in tubers
- Longer shelf life in final produce such as onions.
The versatility of these micron-sized granular fertilizers, particularly their flexibility when it comes to the choice of application method, is an added advantage. Both products are suitable for various farming practices – including micro-irrigation (drip) systems, sprinklers, overhead irrigation equipment, or conventional broadcasting and seed drill fertilizer applications.
“Our R&D is continuously working towards providing more and more innovative solutions in the plant nutrient as well as the crop protection space,” Bimal Shah, SML’s managing director, told Fertilizer International. “Our products reduce the overall impact on the environment while providing the most efficient, efficacious and cost-effective solutions to the farming community.”
SML’s product range is now offered to farmers in over 80 countries. Advantageously, being OMRI-certified, Techno-S® and Techno-Z® are approved for organic farming too.
Having achieved rapid growth and adoption of these products in India, SML has now successfully established a firm foothold in the Turkish agricultural market. “This year we are gearing up for some mega launches in Brazil and Europe alongside our continued focus in the US,” said Bimal Shah.
Fertigation, the application of nutrients via an irrigation system, is a niche but high-value agricultural market for sulphur. Thiosulphates, in particular, are widely-used as liquid sulphur fertilizers in the broad acre and speciality crop market in North America and Europe. Their use is also on the increase in Latin America.
Tessenderlo Group is a global leader in speciality liquid fertilizers and manufactures four main thiosulphate products:
- Ammonium thiosulfate, Thio-Sul (12% N + 26% S)
- Potassium thiosulphate, KTS (25% K + 17% S)
- Calcium thiosulfate, CaTs (6% Ca +10% S)
- Magnesium thiosulfate, MagThio (4% Mg + 10% S)
Thiosulphates offer sulphur in both immediately plant-available form and in slower release form available to plants over a longer time period. Thiosulfates also have a modest acidification effect, benefitting crops grown on alkaline (calcareous) soils.
According to Tessenderlo, providing sulphur to crops via thiosulphates can offer the following specific benefits:
- Enhances crop protein and chlorophyll content
- Assists the synthesis and functioning of enzymes in the plant
- Optimises fertilizer efficiency by stabilising nitrogen
- Improves availability of nutrients in the soil, particularly phosphorus and micronutrients, and their uptake by the crop
- Energy efficient assimilation in the plant
- Provides prolonged sulphur nutrition
- A controlled and localised pH adjustment effect in the soil.
Thio-Sul is suitable for a variety of application methods and, alongside nitrogen, delivers sulphur as ‘active’ thiosulphate. It also improves phosphorus uptake and can be added to urea ammonium nitrate (UAN) to improve nitrogen use efficiency.
KTS is one of the most concentrated forms of liquid potassium and sulphur available on the market. It is marketed as a fast-acting and flexible liquid potassium crop quality improver, particularly in fertigation applications. The product is suitable for booster or starter formulations and can also be applied as a foliar fertilizer when crop demand for potassium is high.
When combined with liquid ammonium polyphosphate (APP), KTS can be applied as an effective starter fertilizer early in the plant’s growth cycle. The presence of KTS improves phosphorus use efficiency by regulating the rate at which polyphosphates turn into orthophosphates and becomes plant available.
Thio-Sul has a powerful acidification effect by combining the ammonium cation with thiosulfate. Thio-Sul also provides two particular benefits when combined with UAN solutions:
- It brings sulphur as a nutrient into the mix – the correct N/S ratio being very important for most crops
- It acts as nitrogen stabiliser improving nitrogen use efficiency.
Various studies suggest that Thio-Sul and CaTs both have the ability to inhibit the urease reaction, thereby reducing nitrogen loss via ammonia volatilisation, as well as slowing down nitrification by reducing the loss of nitrogen though nitrate leaching.
CaTs, as well as offering a nitrate- and chloride-free source of calcium, and providing thiosulfate sulphur, also acts as a soil conditioner. Being a highly-soluble liquid form of calcium – unlike gypsum – CaTs is effective at penetrating the soil profile where it acts as a flocculant, opening up soil pores and improving soil structure and drainage. It can also help displace undesirably high levels of sodium in soils.
(Note: Thio-Sul, CaTs, MagThio and KTS are registered trademarks of Tessenderlo Group NV/SA.)
US sulphur fertilizer use increasing
The use of sulphur fertilizers is increasing in the Midwestern US, according to research published in Communications Earth & Environment in December. This scientific paper compared sulphur fertilizer application rates across 12 Midwestern states with the declining rates of atmospheric sulphur deposition.
The researchers from the University of Colorado and Syracuse University found that almost all the decline in atmospheric sulphur deposition was being replenished by the field application of sulphur fertilizers.
Data from the US National Atmospheric Deposition Program showed that the rate of sulphur deposition on Midwestern croplands fell from 4.7 kg/ha in 1987 to 1.1 kg/ha by 2017. This was due to the progressive removal of sulphur from vehicle fuels and the scrubbing of sulphur dioxide from power plant emissions.
In contrast, fertilizer sales data from the Association of American Plant Food Control Officials showed that sulphur application rate from the use of sulphur-containing fertilizers increased from 0.1 kg/ha in 1985 to 4.9 kg/ha in 2015. This increase almost completely replaced the loss of ‘free’ sulphur from declining atmospheric deposition.
Despite this, the researchers concluded that the need to add sulphur fertilizers to soils will continue to rise – given the competing priorities of air quality regulation and high agricultural productivity – both in the US and many other parts of the world.
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