Mobility within tree:  Fair

Uptake Form: SO₄^2-

Function: some amino acid/protein, protoplasts, enzymes

Deficiency/Toxicity Symptoms:  Deficiency of S is not usual but may occur in light texture soils and in orchards that irrigated with very pure water. Visual symptoms of S deficiency are similar to N deficiency. Younger leaves will show yellowing with sulfur deficiency which is similar to N deficiency.  Some chlorosis may occur as well. Use soil and leaf tissue testing to assess S needs. Occasional use of S based fertilizer (gypsum, ammonium sulfate, zinc sulfate, etc.) will prevent or correct deficiencies (Sallato et al. 2019). Sulfur toxicity is usually not a problem.

Sulphur is required to perform vital functions such as chlorophyll and protein formation, enzymes and vitamins development, cold and drought resistance and N fixation in legumes (Sharifi et al., 2011). Sulphur for plant growth is taken mainly from two reservoirs, the soil and the atmosphere. Typically 90% of total soil S exists as organic S, and this must be mineralized, or converted to S by microorganisms, to be available to the plant. Sulphate is soluble in soil water, and in this form, plant roots can easily absorb the nutrient. Sulphur dioxide (SO₂) in the atmosphere also supplies S to plants.

Sulfur Sources and Application

            A sulphur fertilization recommendation is issued by some laboratories when the soil sulphur level is 25 µg S/mL soil or less. This soil test level is used to ensure sulphur adequacy for all crops grown in British Columbia. Ensuring immediate adequacy can be realized at little or no cost by using a fertilizer that contains sulphate-sulphur as a secondary nutrient. Some common sources of S for tree fruits include elemental S (100%; low solubility; soil application only), SulPo-Mag (langbeinite: K₂Mg₂(SO₄)₃; 22%), gypsum (calcium sulphate; 19%; soil application only), ammonium sulphate (24%), Epsom salts (magnesium sulphate; 13%), potassium sulphate (18%) (Sharifi et al. 2011).  Ammonium sulfate (21-0-0) should only be used on calcareous (pH above 7) soils since ammonium is released and forms acid.