Sulfur Fertilizers

Sulphur (sulfur, S) is an important plant nutrient essential to produce healthy plants with high yields. No matter the crop, fruit, vegetables, grains, or pasture crops, they all need sulfur to reach their full yield potential. This important secondary macronutrient plays a role in soil health and fertility, contributing to the overall sustainability of agricultural ecosystems.

Why has the need for sulfur inputs increased across Canada?

In the past, sulfur deficiency wasn’t a major concern for growers across Canada due to ample supplies from organic matter and sulfur emissions. Industrial processes provided much of plants’ sulfur needs through atmospheric release. Yet, in the last three decades, recent legislation aimed at improving air quality has reduced sulfur emissions and drastically lowered atmospheric sulfur availability in North America. Coupled with increased crop productivity leading to higher sulfur uptake during harvest, both visible and hidden sulfur deficiencies are now more common in many regions. With agriculture’s expanding scale depleting soil sulfur further, the demand for sulfur and sulfate-based fertilizers has grown.

What is the role of Sulfur in plant development?

Adequate sulfur levels in soil promote optimal crop growth, development, and yield.  Sulfur is essential for:

• Protein formation & synthesis: Sulfur is need for plants to form proteins, enzymes, vitamins, and chlorophyll. In legumes, it is crucial in nodule development and efficient nitrogen fixation. Protein synthesis requires large amounts of sulfur, especially for the formation of oils within the seed. As a constituent of several amino acids and vitamins found in plants and animals, sulfur is critical for determining the nutritional quality of foods.
• Photosynthesis: Sulfur is also essential for photosynthesis and contributes to crop winter hardiness.
• Nutrient Balance: Sulfur interacts with other essential nutrients like nitrogen, phosphorus, and potassium, influencing their availability and uptake by plants. Maintaining a balanced nutrient profile, including sulfur, is crucial for maximizing crop productivity and quality. In fact, an adequate supply of sulfur is crucial, not only for crops with high sulfur requirements – such as legumes (alfalfa, clover, soybean, etc.) and Cruciferae (canola and rapeseed) – but also for crops with high nitrogen requirements (maize and cotton), which require sulfur to optimize their nitrogen utilization.
• Yield and Quality Improvement: Adequate sulfur levels in soil promote optimal crop growth, development, and yield. Sulfur deficiency can result in reduced crop yields, poor quality produce, and increased susceptibility to pests and diseases.

Symptoms of Sulfur Deficiency

Pale green leaves, starting first on younger leaves, indicate sulfur deficiency. Eventually, the whole plant will have a light yellow-green appearance. Plants displaying sulfur deficiency often appear smaller with stunted growth. Learn more about sulfur deficiency here!

What is elemental sulfur vs sulfate?

Elemental sulfur requires microbial oxidation to convert into sulfate form before it can be utilized by plants, while sulfate-based fertilizers provide sulfur in the immediately available sulfate form. Sulfate-based forms, like Ammonium Sulfate (AMS) and Sulfate of Potash (SOP) are more readily available to the crop, but also prone to leaching in high rainfall environments. Polyhalite (sold as Polysulphate) is also sulfate-based, but since its natural mineral composition dissolves more slowly, making it immediately available in a gradual release form, releasing over the season. The choice between forms often depends on factors such as soil conditions, crop requirements, and application timing preferences and agronomic goals.

Why is Polysulphate (polyhalite) considered a superior form of sulfur?