Agronomy Tech Tips: Sulfur in Crop Nutrition

Sulfur is a secondary macronutrient and is essential for crop production.

Sulfur plays a big role in forming proteins in plants, which are fundamental for plant structure and function. Sulfur also contributes to chlorophyll formation, is necessary for the development of root nodules, and plays a critical role for the plants’ metabolic processes. Sulfur is commonly supplied through commercial fertilizers. Below are several dry and liquid options with brief descriptions.

Dry Fertilizer

12-40-0-10S (MicroEssentials® S10)

A granular fertilizer providing N, P, and S in a single granule with advanced technology for season long nutrient release. The sulfur element provides both quick release sulfate and slow-release elemental sulfur for continuous nutrient supply.

90% Elemental Sulfur (90% Sulfur)

90% Elemental Sulfur is a granular product commonly mixed with dry fertilizer blends as a sulfur source. Elemental sulfur is water insoluble and is not immediately available to crops, soil microbes must convert it to sulfate before plants can absorb. This process can be slow and depends on the environment (temperature, moisture, soil health). Because of the process, elemental sulfur would be best suited for fall applications. Unlike readily soluble sulfate forms, elemental sulfur resists leaching until it is converted to sulfate.

Polysulphate (19.2% S, 14% K, 3.6% Mg 12.2% Ca)

Dry fertilizer sulfur source with other nutrient values, Polysulphate contains 4 in one natural fertilizer containing sulfur, potassium, magnesium, and calcium. The nutrients are released gradually over time, reducing leaching risk and matching plant uptake needs. This is a good option for fall, winter, spring or summer application.

Calcium Sulfate (Gypsum 22% Ca17% S)

Calcium sulfate, commonly known as gypsum, is a dry granular product and applied with dry fertilizer application equipment. It is fertilizer and soil amendment.The fertilizer component provides calcium and sulfur which are essential crop nutrients. Calcium sulfate can improve soil structure by loosening compacted soils and prevent crusting, enhance water infiltration and retention. It benefits various soil types, especially heavy clays.

Ammonium Sulfate AMS (21-0-0-24)

Ammonium Sulfate is a dry granular product that is applied with dry fertilizer application equipment. The fertilizer source provides plants with two essential nutrients, nitrogen and sulfur, the sulfur is highly soluble. Ammonium sulfate applications can benefit highly alkaline soils by helping to lower the pH.

Liquid Fertilizer

Ammonium Thiosulfate ATS (12-0-0-26)

Ammonium Thiosulfate is a liquid fertilizer providing nitrogen and sulfur to crops. It is commonly added to liquid nitrogen application. The sulfur source is thiosulfate form, is not plant available and has to react with soil to convert to sulfate. This process takes place in the presence of bacteria and is driven by moisture and temperature. A good rule of thumb is that one half becomes plant-available within a week after application depending on soil temperature and moisture,so ATS can be used as herbicide carrier. In certain situation these combinations can cause incompatibilities issues leading to uneven mixing and application of herbicide. Addition of water to the mix can help resolve this problem. ATS can inhibit germination and damage roots, hence it is not recommended for in-furrow applications.

Foliar Feed

MicroEdge Sulfur (7-0-0-10)

MicroEdge Sulfur is a liquid nutrient option for foliar application to provide immediate nutrients to the crop. Common use rates are 1-2 quarts/acre and are designed to feed the plant at that given stage of application. This is a supplemental option to fulfill a nutrient need during peak nutrient uptake or during a stress period. MicroEdge Sulfur can be applied with post-emerge herbicide and fungicide.

Choose the Right Source

Sulfate: Immediate availability for plant uptake (e.g., ammonium sulfate, gypsum, part of sulfur in MicroEssentials® S10, Polysulphate).

Elemental Sulfur: Requires conversion to sulfate by soil microbes; best applied in the fall for the following season (Elemental Sulfur, part of the sulfur in MicroEssentials® S10).

Application Recommendations

Corn Application Rates

Corn is highly responsive to sulfur, especially on soils with <3.5% OM.

Sandy/Coarse Soils: Apply 25 lbs S/acre broadcast or 10–12 lbs S/acre in a starter fertilizer band

Fine/Medium Soils: Apply 10–15 lbs S/acre broadcast

Nitrogen-to-Sulfur (N:S) Ratio: For optimal nitrogen use efficiency, target an N:S ratio of 10:1 to 12:1 (e.g., 1 lb S for every 10 lbs of N applied)