Increasing sulfur a concern in field crops

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When you are planning your 2012 fertilizer program, you might want to consider if your fields might benefit from supplemental sulfur (S). The 2010 International Plant Nutrition Institute (IPNI) Report and recent research publications have highlighted declining soil S levels and foliar deficiency symptoms in crops, particularly in the Western Corn Belt. Recently, Ontario Ministry of Agriculture, Food and Rural Affairs  cereal specialist Peter Johnson said that he was able to remedy foliar deficiency symptoms in wheat by adding S containing fertilizers. Atmospheric deposition used to supply a considerable amount of plant available S (about 8-15 lbs./A annually), but with the implementation of the Clean Air Act, this amount has significantly decreased. Another important source of S is the soil organic matter. When organic matter decomposes, S is released into the soil solution. Plant roots take up S from the soil primarily as negatively charged sulfate ions. In this form, it is also subjected to leaching and microbial immobilization.

In Michigan, sulfur deficiencies are most likely to occur on crops growing in coarse-textured soils with low organic matter. Michigan crops that are most likely to benefit from S application are alfalfa, wheat, soybeans, corn, potatoes and canola. In corn, yellow strips on light green leaves with symptoms of interveinal chlorosis early in the season are common and may indicate S deficiency. These symptoms can also resemble magnesium deficiency. Sulfur is not mobile within the plant, so symptoms appear in the new growth. Plants usually grow out of this condition as roots penetrate the subsoil. However, because of the many light-colored sandy soils with low organic matter in Michigan, more intensive cropping systems and lack of S impurities in major fertilizers may have increased the need for supplemental S.

Soil tests for S are helpful, but not as accurate as tissues tests. This is because organic matter decomposition is capable of generating significant amounts of S. The S sufficiency range for most crops based on tissue tests falls between 0.20 to 0.50 percent. This information is found in MSU Extension Bulletin E-486, “Secondary and micronutrients for vegetables and field crops.”

For correcting deficiencies, an application rate of 20 to 40 lbs./A of S is adequate. Soluble S sources are potassium sulfate, ammonium sulfate and Epsom salt. Gypsum is hydrated calcium sulfate which is moderately soluble. Elemental S is not immediately effective, but may be a useful part of a long-term S management plan. Elemental S has to be first converted to sulfate by soil microorganisms. Foliar sprays of S are readily absorbed by plants when used as a fungicide, but it is not a recommended practice to correct deficiencies on field crops. You may want to consult your fertilizer dealership about special N-P-K blends of fertilizers with supplemental S. Animal manure and organic amendments such as compost and biosolids are an economical and effective source of S. In 2012, we plan to conduct some on-farm tests to study the sulfur response of soybeans on coarse-textured soils.

For further information about sulfur, read MSU Extension Jim Isleib’s article, “Crop requirements for sulfur vary.”

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