Michigan State University Extension
Soils & Soil Management - Fertilizer - 05209704
07/10/97
Secondary and Micronutrients for Vegetables and Field Crops Extension Bulletin E-486, Revised August 1994
By M.L. Vitosh, D.D. Warncke and R.E. Lucas Department of Crop and Soil Sciences Michigan State University Extension
Plants take up sulfur primarily as sulfate ions (SO4=). In the plant, it is reduced and assembled into organic compounds. Sulfur is a constituent of certain amino acids (cystine, cysteine, glutathione and methionine) and the proteins that contain these amino acids. It is found in vitamins, enzymes and co-enzymes. Sulfur is present in glycosides, which give the characteristic odors and flavors to mustard, onion and garlic plants. It is also required for modulation and nitrogen fixation of legume. As the sulfate ion, it may be responsible for activating some enzymes.
Sulfur in Michigan Soils
In soil, sulfur is present primarily in the organic form, which becomes available when organic matter decomposes. The available sulfate ion (SO4=) remains in soil solution, much like the nitrate ion (NO3-), until it is taken up by the plant. In this form, it is subject to leaching as well as microbial immobilization. In waterlogged soils, it may be reduced to elemental sulfur (S) or other unavailable forms. Fertilizer impurities also contribute to the total supply of available sulfur in soils.
Atmospheric deposition supplies a considerable amount of plant-available sulfur. For rural areas of Michigan, the amount will generally vary from 8 to 15 pounds per acre annually, depending on proximity to an industrial emission source. Precipitation within several miles of certain industrial sites may contain 10 to 20 times as much sulfur as precipitation in more rural areas. Sulfur dioxide in the atmosphere can also be absorbed through the leaves of plants. Once absorbed, it is rapidly converted to the sulfate ion.
Because of the many light-colored sandy soils in Michigan, more intensive cropping systems and increased use of fertilizers low in sulfur, one might expect sulfur deficiency to be widespread. Field trials, however, have shown little need for additional sulfur fertilizer Soil mineral sources and sulfur fallout from the atmosphere currently provide adequate sulfur for crop production in Michigan.
Sulfur Deficiency Symptoms
Sulfur-deficient plants are generally light green, similar to plants with nitrogen deficiency (Vis. 4), (Vis. 5). The most likely crops to show a sulfur deficiency are those grown on sandy, low organic matter soils in northern Michigan. Legumes, especially alfalfa and others with a high sulfur requirement, will normally be the first crops to respond to sulfur fertilization. Dry edible beans that were not adequately fertilized with nitrogen have been shown to respond to sulfur fertilizer. Corn, small grains and other grasses are less likely to show sulfur deficiency.
Correcting Sulfur Deficiency
Sulfur research in other states has led to the development of several methods for extracting available sulfur from soils. The interpretation of these tests, however, continues to be a problem. Consideration of available sulfur from subsoil and atmospheric contributions may be necessary to accurately predict response to added sulfur fertilizer.
Application rates of 20 to 40 pounds of sulfur per acre will correct a sulfur deficiency. Soluble sources of sulfur such as potassium sulfate, potassium magnesium sulfate, Epsom salts, ammonium sulfate or gypsum are usually preferred to elemental sulfur. For most soils, one application is sufficient for 2 or 3 years. Very sandy soils, where leaching is a problem, may require larger or more frequent applications.
Sulfur Toxicity
Sulfate/sulfur toxicity symptoms begin as an interveinal chlorosis and scorching of the leaf margins, which gradually proceeds inward. Sulfur toxicity has not been observed in Michigan.
Irrigation water high in sulfate and/or soluble salt, a potential problem source normally occurring in arid and semi-arid regions, is often remedied by thorough leaching. Excessive sulfur in some organic soils and so- called Kett clay soils can cause extreme acidity when sulfur is oxidized because of drainage.
Sulfur dioxide in the atmosphere is an air pollutant that can injure plants. Plants relatively sensitive to sulfur dioxide injury are soybeans, dry edible beans, alfalfa, small grains and many vegetable crops. The symptoms of sulfur dioxide injury may resemble damage from frost, other air pollutants, chemical sprays or herbicide residues in soils. This often makes it very difficult to identify the cause of injury. Positive identification can be made only after all foliar symptoms and related evidence have been considered.
In general, symptoms are either chronic or acute, depending on the rate of sulfur accumulation in the leaf tissues. Chronic injury is characterized by a slow accumulation causing a general chlorotic appearance. Some plants may be ivory or white, while others show a strong reddish brown or black coloration. Later symptoms resemble normal senescence.
Acute injury appears as marginal areas of dead tissue, which at first have a grayish green, water-soaked appearance. Later these areas take on a leached ivory color in most plants. In small grains, tip dieback is a common symptom.
| Visual title - Visual size | Visual title - Visual size |
|---|---|
| Sulfur-deficient dark red kidney beans - 35K | Sulfur-deficient corn - 39K |
