Cover St ory
Managing Calcium, Magnesium and Sulfur in
Turf
By Tom Samples, Ph.D.; John Sorochan, Ph.D.; and Adam Thoms, Plant Sciences Department, The University of Tennessee
In
order to be classified as “essential,” a chemical element or nutrient must be required by a plant for healthy growth and development. Atmospheric carbon dioxide supplies turfgrasses with carbon, while water is the source of both hydrogen and oxygen. Turfgrasses take up the remaining 14 essential nutrients (mineral nutrients) from soil. An essential mineral nutrient may be required in large (macronutrient) or very small (trace or micro) quantities. Due to the amounts needed by turf-
14
grasses, nitrogen (N), phosphorus (P) and potassium (K) are categorized as primary macronutrients. Although calcium (Ca), magnesium (Mg) and sulfur (S) are categorized as secondary macronutrients, they are no less important than N, P and K.
Sources and plant-available forms of Ca, Mg and S in soils Calcium, the fifth-most-abundant mineral nutrient in the earth’s crust (4.2% by weight, Table 1), comes from weathered rocks and minerals, including anorthite,
TENNESSEE TURFGRASS December/January 2014 Email TTA at: tnturfgrassassn@aol.com
apatite and biotite. Calcite (calcium carbonate — CaCO3), dolomite (calcium carbonate + magnesium carbonate — CaMg(CO3)2) and gypsum (calcium sulfate — CaSO4) are also sources of Ca. Magnesium is the eighth-most-abundant mineral nutrient on earth. In addition to dolomite, many types of silicates (for example, augite, biotite, hornblende, muscovite and olivine) contain Mg. Sulfur occurs naturally as a pure element (native S) and as sulfide (pyrite — iron sulfide; sphalerite — zinc sulfide)