How much sulfur do plants need for optimal growing?
Both the yield and quality of crops grown on sulfur-deficient soils are reduced unless supplemental sulfur is included as fertilizer. Sulfur can increase crop yields and quality and result in significant economic returns to producers. It also improves fertilizer efficiency.
Sulfur is an important mineral nutrient. It’s a component in two amino acids that are in proteins. Proteins are the catalysts of life in plant cells. Without proteins, life would not exist as we know it. Proteins are simply linear chains of amino acids. Amino acids require carbon, hydrogen, nitrogen and oxygen, but the amino acids cysteine and methionine also require sulfur.
Sulfur is a secondary plant nutrient, along with calcium and magnesium. Plants generally require about as much sulfur as phosphorus. While farmers regularly apply phosphorus, they rarely apply sulfur.
Most crops require 12 to 25 lbs. per acre (15 to 30 kg per hectare). Oil crops, protein crops, legumes and forages (alfalfa) require more sulfur than phosphorus for optimal yield and quality. Agronomists usually recommend applying 15 to 30 lbs. of sulfur per acre. The lower end of that scale is recommended for grain crops and the higher end for oilseed and forage crops.
Soil tests aren’t reliable measures of sulfur because sulfur in the soil is very dynamic and fleeting. A tissue test can be used to measure sulfur concentration. Sulfur concentration should be from 0.20 to 0.25%. The most important ratio is nitrogen (N) to sulfur (S), and it should be in the range of 10-15 parts nitrogen to 1 part sulfur. Ratios of 18-20 or greater to 1 indicate a sulfur deficiency.
Gypsum (calcium sulfate) is an excellent source of sulfur, very soluble, readily available and economical.
Dr. Davidson posts articles on soil management and subjects to gypsum. If you have suggestions for topics or questions, feel free to contact him at [email protected] or call 402-649-5919.