Illinois Fertilizer & Chemical Association
Supply · Service · Stewardship

Corn Response to Sulfur in Illinois

F.G. Fernández, S. Ebelhar, K. Greer, and H. Brown
Corn (Zea mays L.) is the most important crop in Illinois and is grown under many different soil and environmental conditions. Sulfur (S) has long been recognized as one of the essential elements for plant development. This nutrient has been classified as secondary, even though it is required in amounts similar to those of phosphorus by the corn crop. The frequency of S deficiency in corn has increased over the years since it was first seen in Illinois over three decades ago. This increase in frequency of S deficiency is likely the result of several factors, including less incidental S in fertilizers, insecticides, and fungicides; less atmospheric S deposition resulting from more rigorous emission standards; greater removal rates by increasing grain yields; increased use of conservation tillage which may reduce S availability; and fewer livestock operations causing less application of manure (Lynch, et al., 2000; Sawyer and Ebelhar, 1995).

Corn demand on the natural soil supply of S may be creating deficiencies because S fertilizers are typically not used. The primary source of S for corn comes from organic matter (OM). However, this organic S has to be oxidized by microbes to sulfate (SO42-) before it can be utilized by the crop. Since this ion can be leached as rain water moves through the soil, it is not possible to accumulate S in the soil. Thus, S supply to the crop is dictated in large measure by microbial activity. Factors such as temperature and soil water content have an important impact on S availability. Most often S deficiencies are observed in low OM soils and coarse-textured soils where S can be easily leached out. However, S response in crops has been reported on soils that do not have these characteristics (Feyh and Lamond, 1992; Hoeft et al., 1985; Randall et al., 1981). Some of the additional conditions in which S deficiencies may occur include soils with low subsoil S supply capacity, and fine-textured soils that have been eroded.

Research on corn response to S has not been conducted for a long time in Illinois. The last statewide survey to determine corn response to S was a three-year study between 1977 and 1979 (Hoeft, et al., 1985). In that study only 5 out of 82 sites showed a significant corn grain yield response to S. An additional greenhouse study was conducted using the top 9 inches of soil from each location. The greenhouse study showed 60% of the soils were responsive to S application. The difference in response between the field and greenhouse study point out that the surface layer of many of the soils were near their maximum ability to supply S and that subsurface layers of the soil and/or atmospheric deposition are important at supplying adequate S levels for corn uptake in the field. In this early work the S contribution from the subsurface layers of the soil was not investigated. Further, in some of the sites, S deficiencies were observed early in the season, but no differences in grain yield occurred (Hoeft, personal communication). It is possible that the lack of corn-yield response to S application in many of the sites of that study were related to a large supply of S in the subsurface. The fact that S deficiency in some sites was observed only early in the season might indicate that the problem was corrected once the corn roots reached a plentiful S-supply in the deeper layers of the soil. All these evidences point out the need to quantify the S status of the soil in the subsurface.

Since that early study (Hoeft et al., 1985), a combination of increasing uptake of S by higher-yielding crops and a reduction of S inputs from the atmosphere or in the inputs used in farming today might be causing insufficient S supply for corn. In the earlier study by Hoeft et al., yield was increased, on average, over 11 bushels per acre by applying S when the soil was deficient. Inadequate supply can restrict grain yield and uptake of other nutrients. Providing an adequate supply of S is critically important to maximize profits from grain as well as to enhance efficient use of fertilizers and other inputs in the farming system. Thus, our objectives are to determine corn tissue S content and grain yield response to S application, to estimate corn response to S in relation to soil and environmental conditions for the state, and to determine the contribution of subsurface soils to the total supply of S to corn.