Soil Chemistry & Fertility
Part 2 – 70 | Unit 2.2
Lecture 2: Plant Nutrient Requirements & Nutrient Cycles
c) Sulfur (S) (see t Figure 2.13, the Sulphur Cycle)
Sulfur is part of two amino acids (cysteine and methionine) that are incorporated into
proteins. Sulfur is also essential for nodule formation by N-fixing bacteria on the roots of
legumes. It is present in oil compounds that give plants such as garlic and onions their
characteristic odor. (Vidalia onions, known for their sweetness, come from an area that
has low S soils.)
Sulfur deficiency problems can occur if growers rely on fertilizers that are concentrated
with other nutrients (e.g., N, P, and K) but are free of S. Symptoms of S deficiency in
plants include:
i. Pale young leaves, light green to yellowish in color, sometimes with veins lighter than
surrounding tissue. In some plants older tissue may be affected also.
ii. Small and spindly plants
iii. Slow growth rate and delayed maturity
Plants take up S as the sulfate ion So 4 2-. Sulfur is also sometimes absorbed from the air
through leaves in industrial areas where S is in high concentration.
the use of organic residues in amounts to satisfy other nutrient requirements will usually provide
sufficient sulfur. other sources of sulfur include animal manures (S is usually well balanced with N),
langbeinite (Sul-Po-mag—see section above on P), gypsum, and pure S from natural sources (granular
sulfur is preferred since sulfur dust is an explosion hazard).
t fig Ure 2 .13 | the SULFUR CyCLe
Cathy Genetti Reinhard