Sulfur is an essential nutrient for crop growth and development, including a role in amino acid formation, potentially improving the quality of grain and forage in animal feed. This article provides a basic overview of sulfur management, including the sources, rates, and timings that can impact corn yields and nutritive value.

Sulfur Overview

To determine if sulfur application might benefit your corn field, it is important to understand how much sulfur is necessary to grow a good crop of corn. Looking at our Tri-State Fertilizer Recommendations, estimated sulfur requirements are:

• Growing corn for silage: Silage corn removes about 1.1 pounds of sulfur per ton of forage (equivalent to 27 pounds of sulfur per acre when yields are 24 tons/acre).
• Growing corn for grain: Grain corn removes about 0.05 pounds of sulfur per bushel of grain (equivalent to 10 pounds of sulfur when yields are 200 bushels/acre).

Sulfur Sources

Corn’s sulfur requirement can be met from a wide range of sources. Acid rain and other forms of atmospheric deposition of sulfur to soils were historically major contributors of sulfur to corn fields. However, atmospheric sulfur deposition has declined since the 1990s due to changes in air quality regulations. More recent estimates are that Ohio fields receive around 5 to 6 pounds of sulfur deposition per acre per year, sometimes more. Manure is another important sulfur source, and dairy manure typically contains 1.4 to 2.7 pounds of sulfur per 1000 gallons of liquid manure. Atmospheric deposition and a 5000-gallon-per-acre manure application can provide about 16 pounds of sulfur per acre. Fertilizers like monoammonium phosphate (MAP), diammonium phosphate (DAP), and triple superphosphate (TSP) contain around 1.5-2% sulfate. Gypsum, commonly used as a soil amendment, contains around 18% sulfur. Other smaller sources of sulfur entering fields include ammonium sulfate (AMS) and other spray tank additives, micronutrient fertilizers, and some fungicides.

The Four Rs for Sulfur Management

When making sulfur application decisions, consider the 4Rs for nutrient management: Right rate, Right source, Right place, and Right time. For instance, the timing of sulfur application depends on the nutrient source. Plants take up sulfur from the soil in the form of sulfate ions (SO₄^-1). Other forms of sulfur, such as elemental sulfur (S₂) or organic sulfur (compounds with both sulfur and carbon atoms), must be converted to sulfate before they are plant available. Most of the sulfur in DAP, AMS, and atmospheric deposition is usually in the sulfate form and can be immediately available for plant uptake. Sulfur utilization from these sources is higher when they are applied to a growing crop (with existing nutrient demand), since sulfate ions are highly mobile in the soil profile (like nitrogen) and can leach out of the root zone following heavy precipitation events. Manures can contain a mix of sulfate-sulfur and organic sulfur, so around half of the sulfur from manure is available in year 1, and around half will become available in future years after it gets mineralized. If you are looking to correct a S deficiency in the short term during the growing season, products like gypsum (calcium sulfate), AMS, or other sulfate sources are more suitable than sources with mostly organic or elemental S.

Recent Sulfur Application Trial Results

Since 2013, 53 field trials with S applications in corn were conducted in Ohio, primarily with spring-applied sulfur (gypsum, ammonium sulfate, or thiosulfate) before planting, at-planting, or soon after planting. Sulfur applications typically increased S concentrations in leaf tissue and grain, which may improve feed value, but that did not always translate to yield gains. Only 44% of trials showed a positive response to S, but from those positive responses, only 5 trials were statistically significant. These findings suggested that S deficiency is not a widespread problem in Ohio, but some corn fields can positively respond to S fertilization. More recently, four on-farm trials in 2022 and 2023 were conducted in Sandusky County to evaluate silage and grain corn’s response to S fertilizer across two contrasting soil types. Grain yields were maximized with 20 lbs./acre of S, but only in the sandy soil. No statistical differences were found in the clay loam soil. Silage yields did not show statistical increases in yield associated with S fertilization.

Identifying Sulfur Deficiencies

Identifying S-deficient corn fields can help predict which fields may have increases in yield if S fertilizer is applied. The most prominent visual symptom of S deficiency is yellowing of leaves, especially younger leaves towards the top of the plant. Vegetative corn plants may have interveinal striping patterns instead of an even yellowing across entire leaves (Figure 1). A tissue test can be useful for confirming S deficiency. Generally, if corn ear leaves sampled at initial silk have 0.16-5.0% S content, they do not have a sulfur deficiency (0.09-0.15% is considered marginal). More information about sufficiency ranges and tissue sample collection can be found in the Ohio Agronomy Guide and the Plant Tissue Test factsheet.

Summary

Sulfur fertilizer recommendations are becoming more common due to increased crop removal due to higher yields and reduced atmospheric S inputs. Based on current knowledge, a response to sulfur application can be expected in sandy soils, low organic matter, and fields with no or limited history of manure application. If growing corn for silage, larger amounts are needed for the crop. When growing corn and sulfur deficiency is suspected, an application of 15-30 pounds should be adequate.

The Tri-State Fertilizer Recommendations provide more guidance on managing sulfur and provide specifics about when a crop response to S is more likely to be seen.