By Charles Wortmann, Extension Nutrient Management Specialist, Lincoln, and Charles Shapiro, Extension Soil Scientist — Crop Nutrition, Haskell Agricultural Laboratory, University of Nebraska-Lincoln
Sulfur application often results in greener wheat, corn, and sorghum but probably does not result in increased yields on medium and fine texture soils of Nebraska.
Around 30 sulfur application trials have been conducted in Nebraska for corn and sorghum during the last eight seasons. Most were on no-till fields, including 15 high-yielding, irrigated corn sites. The results consistently showed no yield benefit to sulfur application on medium and fine texture soils and support UNL recommendations that profitable sulfur application is likely only on sandy soils that test low in sulfur and have less than 1 percent organic matter.
Row crops have access to sulfur from several sources:
- mineralization from soil organic matter and crop residue, the largest resource;
- irrigation water, which can be a significant source; and
- manure applications.
The sulfate ion is very mobile in soil water and can be easily leached from the root zone. The soil test for sulfur availability is not very reliable and soil organic matter and texture have proven to be more useful in assessing soil capacity for sulfur supply.
We recognize the need to have on-going evaluation of our recommendations to ensure their validity for high, as well as moderate, yield situations. For example, corn and alfalfa yield responses to applied sulfur have been observed recently in 28 of 45 northeastern Iowa fields, especially for sandy and/or low organic matter soils. Recent research results confirm that yield response to sulfur application is unlikely in western Iowa.
We are currently seeking funding to conduct 50-60 replicated strip trials beginning in 2011 on farmer fields with medium and fine texture soils
- where soil matter content is less than 2.5 percent or, on sandy soils where soil organic matter is greater than 1 percent;
- where manure has not been recently applied; and
- where irrigation water sulfur is less than 8 ppm.
If funded, information from these trials will enable us to fine-tune our recommendation, if appropriate.