What does Sulfur (S) do?

In the soil, sulfur interacts with plant roots in two ways: one indirect and one direct. 

The indirect interaction starts when sulfur is converted by soil bacteria to sulfuric acid. This generates acidity and lowers soil pH. Maintaining a balanced pH, neither too high nor too low, gives plant roots easy access to soil nutrients. 

The direct interaction of sulfur with plant roots occurs when they absorb it as an essential plant nutrient. Within the plant, sulfur is a component of two amino acids (the building blocks of proteins) out of twenty total. Sulfur is also a component of many critical vitamins including thiamine (vitamin B1), biotin (vitamin H or B7), and coenzyme A (formed from pantothenic acid, i.e., vitamin B5). These vitamins support the plant's ability to harvest and expend energy, grow healthy membranes, develop root systems, respond to stress, and more.

After the industrial revolution, sulfur deposition from air polution made soil deficiency of this nutrient relatively uncommon. Since the Clean Air Act, sulfur deficiency has become more of an issue to look out for. Sulfur-deficient plants turn yellow and sickly; check out this SoilScoop article on nutrient deficiencies for an example image.

Click here to learn about different types of sulfur ammendments and their impact on your soil.