January 14, 2020
To raise high-yielding crops, sulfur (S) is a key element, yet many soils lack the amount needed to reach maximum potential. Reduced atmospheric depositions, increased yield and crop removal, and high amounts of crop residue are all reasons S deficiencies are becoming more frequent. Sulfur can be one of the most limiting factors in high-yielding corn and soybean production systems. Respectively, 10 pounds of S are removed for a 200 bu/acre corn and a 60 bu/acre soybean crop. Increases in no-till have promoted immobilization and stratification of nutrients. During decomposition, nutrients like nitrogen and S become temporarily unavailable as residue is broken down.
Sulfur deficiency can impact both quality and yield of grain. Sulfur plays an important part in forming proteins, developing enzymes and vitamins, promoting nodule formation, producing seeds, and forming chlorophyll. Adequate S helps seedlings survive in cool, moist soil conditions and helps promote rapid root development during early stages of growth.
Sulfur deficiencies commonly appear as a pale green or yellowish color on lower leaves first and gradually moves across the entire plant. Yellow striping symptoms in corn can be confused with magnesium deficiency (Figure 1). If ever in doubt, send in leaf samples for a diagnosis. Usually, potential yields will already be impacted by the time visual symptoms are noticed, making it more important to be proactive versus reactive with soil fertility plans.
Figure 1. Sulfur deficiency in corn appears as yellowish stripes. Picture courtesy of Jim Donnelly.
Like nitrate, sulfate sulfur leaches in the soil, but not as easily. Sulfur is needed in significant quantities to push yields, especially in sandy soils. Humus is a component of organic matter and is key for holding S in the soil. The higher the humus content, the less likely the need for S. The goal with S fertility is to help ensure it is available to corn post tassel.
Since S is leachable in the soil, fertilizer applications should be made as close to crop need as possible. Many S-containing fertilizers are available, convenient and cost-effective to apply. In season, the most reliable method to determine adequate S levels, is to sample the ear leaf. While sampling this late may not help the current crop, it can provide information needed for the next crop. In general, it is recommended that for loam and loam clay soil types, 15 lb/acre of actual S be applied and for sandy soil types, 25 lb/acre of actual S be applied.
Sources:
Camberato, J. and Casteel, S. 2017. Sulfur deficiency. Soil Fertility Update. Purdue University Department of Agronomy. https://ag.purdue.edu/.
Kinsey, N. and Walters, C. 1993. Hands-on agronomy: Understanding soil fertility & fertilizer use. Greely: Acres U.S.A.
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