Regarding the return on investment for crop nutrition and fertilizer programs, every acre and every nutrient counts, so which nutrients do your crops need most? Most of the time, primary macronutrients take a starring role in nutrient management programs. To a corn grower, nitrogen (N) may be top of mind, along with phosphorus (P) and potassium (K). While soybeans fix a portion of their own N, they can be limited by other nutrients. Despite the emphasis we place on NPK, the reality is that all crops require at least 17 essential nutrients. It is true, some nutrients may have greater importance and limiting effects compared to others, but a balanced fertility program is the cornerstone of high-yielding, superior-quality harvests. 

While sulfur (S) is often overshadowed by N, P, and K, it is a powerhouse macronutrient—and a limiting factor in crop yield and quality. In recent years, there has been greater awareness of the importance of S in modern crop production systems. Sulfur deficiencies have become more commonplace due to changes in emissions controls over the years. In addition, greater productivity from modern crop genetics and unpredictable weather conditions have led to variability in soil organic matter mineralization and leaching losses for nutrients like nitrate and sulfate.

Traditionally, several S fertilizer sources have been used in North American cropping systems. These include common examples like elemental sulfur, ammonium sulfate, and ammonium thiosulfate. All have various pros and cons and can be a good fit for different application types. However, most sulfate-based S sources have a common weakness… availability. The immediate availability of the sulfate-anion for most S fertilizer products may not coincide with the crop growth stage when S is needed most. And sadly, sulfate is prone to leaching if heavy rainfall occurs. With increased focus on soil health, environmental impact, and nutrient innovation, the nutrients and products we focus our dollars on are becoming increasingly important. As an agronomist, finding a sulfur that provides a sustained release to the crop throughout the entire season is now essential to meeting today’s growers’ needs.

That is why there has been so much buzz about Polysulphate. Derived from the mineral polyhalite, Polysulphate is a natural fertilizer containing S (19.2%) but also K (14%), Ca (12.2%) and Mg (3.6%). Mined in the United Kingdom exclusively by ICL, the sulfur in Polysulphate is entirely in the sulfate form. Due to the composition of the mineral, research shows it becomes gradually available to the crop over the course of the growing season. This gradual or prolonged release ensures that S is available during crucial growth stages like rapid vegetative growth and reproductive development. In addition to being a reliable source of S, Polysulphate contributes a low-chloride source of K.

Over the past three growing seasons, ICL has conducted many replicated field trials of Polysulphate in corn, soybeans, and other crops grown in North America. These trials show that yields of Polysulphate are comparable to or greater than other common S sources like ammonium sulfate or potassium magnesium sulfate. Although quality is not the primary economic factor for row crops like corn and soybeans, the Ca and Mg contained within Polysulphate often improves the quality factors as well, which are especially important for specialty crops like fruits and vegetables. Polysulphate’s limited movement in the soil and gradual release profile also reduces the risk of leaching and runoff, making it an ideal choice for fall fertilization.

By using Polysulphate to address yield limitations due to sulfur deficiency, profitability can be increased through extra yield and by indirectly affecting relationships like nitrogen use efficiency. Additionally, because Polysulphate contains four nutrients, all in the same granule, agronomists and growers can consider options to reduce or eliminate other common fertilizer sources like ammonium sulfate, potassium sulfate, or gypsum.

Maybe your fall or spring fertilizer program consists only of NPK. Or perhaps you are looking for exciting new ways to supply S to your crop. Either way now is the time to consider adding a sustainable, gradual release form of S, like Polysulphate, to your fertility program. You can speak with your local retailer to learn more about how Polysulphate can be part of your fertility program for the 2023 growing season.

Jason Haegele, Ph. D, ICL North American Agronomy Lead

Jason Haegele leads ICL’s research collaborations with universities and third-party research contractors in North America to demonstrate the efficacy of ICL products on a broad range of row crops and specialty crops. He is a graduate of the University of Illinois and Iowa State University and has broad range of experience in applied research and field sales support for plant nutrition, adjuvant, crop protection, and biological products.