Elemental sulfur

Elemental sulfur products are formed into granules, prills, or powder from sulfur recovered during fossil-fuel refining or mined directly, then guaranteed at roughly 90% elemental sulfur content. Particle size strongly affects how quickly soil bacteria can oxidise the material.

Chemical form

Elemental sulfur, S⁰

Sulfur content

Approximately 90% elemental sulfur

Availability pathway

Microbial oxidation converts S⁰ to plant-available sulfate over time

Particle size effect

Finer particles have more surface area and oxidise faster than coarse granules

Elemental sulfur supplies sulfur only, and only after soil sulfur-oxidising bacteria convert it to sulfate, a process that occurs over weeks to months depending on soil temperature, moisture, microbial activity, and the particle size of the product applied.

• Sulfur availability is delayed relative to sulfate-based sources
• Oxidation rate depends on soil temperature, moisture, and microbial activity
• Contains no nitrogen, phosphorus, potassium, or other secondary nutrients

Elemental sulfur is used both as a slow-release sulfur source for sulfur-responsive crops such as oilseed rape and onion, and, at higher rates, as a soil acidifier to lower pH ahead of acid-loving crops such as blueberry or to correct alkaline soil conditions.

• Provides a slow-release sulfur supply over an extended period
• Widely used to deliberately lower pH on alkaline or calcareous soils
• Preferred over sulfate sources when acidification, not just sulfur supply, is the goal

Because oxidation and acidification take time, elemental sulfur intended to lower pH is generally applied well in advance of planting, and rates for pH adjustment are typically based on a soil test that accounts for buffering capacity, similar in principle to lime requirement testing but in the opposite direction.

Because elemental sulfur must oxidise before it becomes active, its environmental behaviour differs from that of immediately soluble sulfate fertilizers; once oxidised, the resulting sulfate is mobile in soil in the same way as sulfate from other sources, and over-application for pH adjustment can lower soil pH more than intended.