Is sulfur necessary in agriculture?

Approximately 10% of the sulfur essential for plants, one of the critical macro elements, originates from certain soil minerals (pyrite, marcasite, cobaltite, gypsum, epsomite, mirabilite, etc.), while 90% is derived from the decomposition of organic matter. Although plants can utilize SO₂ from the atmosphere during photosynthesis, this amount is insufficient to meet their sulfur needs. Plants primarily absorb sulfur from the soil through their roots in the form of the sulfate anion (SO₄²⁻). Around 90% of the sulfur absorbed by plants is incorporated into amino acids, proteins, and volatile compounds in the forms of “S-S” and “-SH” bonds. The remaining inorganic sulfur within the plant is mostly found as SO₄²⁻.

Sulfur plays a vital role in the formation of carbohydrates, fats, proteins, and coenzymes within plants. While cereal crops require sulfur at one-third the amount of phosphorus they absorb, legumes need it in a 1:1 ratio, and certain crops, such as cabbage, onion, and garlic, may require up to three times the phosphorus amount. In plants, particularly in those with edible green parts, the nitrogen-to-sulfur ratio can narrow with the application of sulfur fertilizers, helping prevent nitrate accumulation.

To address sulfur deficiencies in agricultural soils and prevent shortages in crop production, sulfur-containing chemical fertilizers (labeled as SO₃ on fertilizer labels) should be used. Application rates should be determined based on soil and plant analysis. Beyond fertilization, elemental sulfur (S⁰) is recommended for effectively reducing soil pH levels, particularly in high-pH soils, thereby enhancing sulfur availability. When applied to soils, elemental sulfur is gradually converted into the plant-available SO₄²⁻ form through microbial activity. This process does not lead to negative outcomes such as soil salinization or plant toxicity; on the contrary, the resulting pH reduction promotes the uptake of other essential macro and micro nutrients (excluding molybdenum) by plants.

Prof. Dr. Murat Ali TURAN