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Sulfur (S) is a part of every living cell and is important to the formation of proteins. Unlike the other secondary nutrients like calcium and magnesium (which plants take up as cations), S is absorbed primarily as the SO42- anion. It can also enter plant leaves from the air as dioxide (SO2) gas.

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Sulfur is present in several organic compounds that give the characteristic odors to garlic, mustard and onion.

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Sulfur appears in every living cell and is required for synthesis of certain amino acids (cysteine and methionine) and proteins.

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Sulfur is also important in photosynthesis and for winter crop hardiness.

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Although S isn't a constituent of chlorophyll, it's still vital in chlorophyll formation.

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Sulfur aids in seed production.

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Leguminous plants need S for efficient nitrogen fixation.

Dig Deeper: Fertilizer Use Guide

Sulfur is supplied to plants from the soil by organic matter and minerals, but it is often present in insufficient quantities and at inopportune times for the needs of many high-yielding crops. Most S in the soil is tied up in the organic matter and cannot be used by plants until it is converted to the sulfate (SO4-2) form by soil bacteria. That process is known as mineralization.

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Deficiency Symptoms

Symptoms of deficiency can vary across crop species, but similarities exist for how nutrient insufficiency impacts plant tissue color and appearance. Nutrient deficiencies are commonly associated with the physical location on the plant (i.e., whether the symptoms are primarily observed on older versus newly formed plant tissue), but these symptoms can spread as the severity of the deficiency progresses.

All photos are provided courtesy of the International Plant Nutrition Institute (IPNI) and its IPNI Crop Nutrient Deficiency Image Collection. The photos above are a sample of a greater collection, which provides a comprehensive sampling of hundreds of classic cases of crop deficiency from research plots and farm fields located around the world. For access to the full collection, you can visit IPNI's website.