Sulfur deficiency in corn
Sulfate‐S is relatively mobile in most soils (similar to nitrate) because it has a double negative charge and is repelled by the negative charge of the soil, unlike nutrients such as potassium, calcium, or magnesium. Although SO4‐S can bind to iron and aluminum in the soil, these elements are much more likely to bind phosphate at the exclusion of SO4‐S. As a result, SO4‐S is easily leached from soils, especially sandy soils.
At the field level the occurrence of S deficiency may be highly variable since soil S availability varies considerably with soil organic matter and texture. Sulfur deficiency is often seen in sandier, lower organic matter, and higher elevation areas of a field while lower lying, higher organic matter, and heavier textured areas typically have sufficient S.
Soil testing methods measure the SO4‐S form of S. Unfortunately soil testing is not particularly useful for predicting S deficiency because it does not take into account the organic S component that might become available to the crop. The SO4‐S component that is actually measured may also be leached from the soil between the time of sampling and the time of crop need. Sulfur deficiencies are notoriously transient because as the season progresses crops often access S deeper in the soil profile and warmer temperatures result in S mineralization from OM and crop residues.
click image to zoomJeff NagelFig. 2. Areas of sulfur deficiency (pale green) and sufficiency (dark green) in an Indiana corn field caused by variations in soil properties. Young corn that is sulfur deficient may show striping as well as an overall yellow color. Identifying Sulfur Deficiency in Corn
Sulfur deficient corn typically has an overall yellow appearance (see Fig. 2) similar to N deficiency. However S is not as mobile in the plant as N, so lower leaves do not show more severe deficiency symptoms than the upper leaves. If a S deficiency is misdiagnosed as a N deficiency the application of fertilizer N will make the S deficiency worse, so tissue sampling is recommended to positively identify which nutrient is deficient. In corn, S deficiency may also cause leaf striping (see Fig. 2) which is easily confused with magnesium, manganese, and zinc deficiency.
The best way to identify a S deficiency is by tissue sampling from the area suspected of deficiency and a healthy area of the field for comparison. In plants less than 4 leaf collars, sample the whole plant beginning about ½” above the soil surface and collect 15 to 20 plants to represent each area. For larger plants, sample the youngest collared leaf (also referred to as the most recently matured leaf) and collect 10 to 15 leaves to represent the areas. Wash soil from the tissue samples with distilled or deionized water. If samples are contaminated by soil they can be rinsed quickly in cold distilled water, but do not overdo it because some nutrients, especially potassium, may be leached out of the tissue. Wet samples should be air‐dried before shipping to the laboratory in paper bags.