Sulfur deficiency in corn
Naturally‐occurring mined gypsum and several by‐product sources of gypsum can be applied to provide S as well. Gypsum if pelletized can be blended with other fertilizers or if ground, applied with a lime spreader. Unless pelletized, however, higher than necessary rates of S will be applied with gypsum which is difficult to spread at rates less than 500 to 1000 pounds per acre (85 to 170 pounds of S per acre assuming 17 percent S). If carryover of S occurs, the S will be utilized in later years. However, in sandy soils, where leaching is likely, the benefit in future years may be minimal. Elemental S must be oxidized by soil bacteria to SO4 before becoming plant available. Warm temperatures and good moisture and aeration are required for S‐oxidizing bacteria to function. Sulfur oxidation is minimal at soil temperatures less than 50° F. Even at 75° F the oxidation rate of S is about 15 percent of that at 85° F, so peak rates of S oxidation do not occur until late spring. Since the availability of elemental S may be minimal in early spring, a fertilizer containing some SO4 in addition to elemental S is preferred over a fertilizer with elemental S alone.
Effects of Sulfur Containing Fertilizers on Soil pH
Soil pH is lowered by elemental S, ammonium thiosulfate, and ammonium sulfate. The oxidation of elemental or chemically reduced S (thio‐S for example) creates acidity which lowers soil pH. However, no acidity arises from the sulfate in any of the fertilizer materials including ammonium sulfate. With ammonium sulfate the conversion of ammonium to nitrate is the component that generates the acidity. When used to provide less than 30 pounds S per acre, the amount of acidity generated by each of these acid-producing fertilizers is equivalent to less than 100 pounds of limestone per acre. None of the S containing fertilizers in Table 1 increase soil pH.
References used in this article:
(1) Camberato, Jim and Shaun Casteel. 2010. Keep an eye open for sulfur deficiency in wheat. Purdue University Department of Agronomy, Soil Fertility Update. Available at: http://www.agry.purdue.edu/ext/soybean/Arrivals/04‐13‐10_JC_SC_Sulfur_deficiency.pdf. (URL accessed May 2012).
(2) Sawyer, J.E., B. Lang, and D.W. Barker. 2012. Sulfur fertilization response in Iowa corn and soybean production. Proc. of the 2012 Wisconsin Crop Manage Conf. 51:39‐48. http://www.soils.wisc.edu/extension/wcmc/2012/pap/Sawyer_1.pdf(URL accessed May 2012).
(3) Zublena, J.P., J.V. Baird, and J.P. Lilly. 1991. Nutrient content of fertilizer and organic materials. http://www.soil.ncsu.edu/publications/Soilfacts/AG‐439‐18/AG‐439‐18.pdf. (URL accessed April 2012).
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