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Sulfur

Sulfur is the most important secondary nutrient and is often considered the “fourth macronutrient.” It plays a key role in plant development, helping with chlorophyll formation, protein synthesis, and nutrient utilization. As yield goals have increased, so has the need for precise sulfur management. Crops require more sulfur today than in the past, yet the natural availability of this nutrient has decreased significantly.

Historically, sulfur was supplied to the soil through atmospheric deposition from industrial emissions and acid rain. As environmental regulations reduced these sources, the “free” sulfur farmers once relied on began to disappear. Despite this change, some soil tests continued to omit sulfur recommendations as recently as a decade ago. Today, most labs include sulfur as a standard part of soil analysis, reinforcing its growing importance in crop nutrition programs.

Managing Sulfur in the Soil

Sulfur is present in the soil in multiple forms, but the plant-available form is sulfate (SO₄²⁻). Because sulfate is highly mobile, especially in sandy or low-organic-matter soils, it is prone to leaching. This makes timing and placement of applications critical. Many growers apply sulfur alongside nitrogen through 2×2 at planting, sidedress, irrigation, or foliar treatments. However, it’s essential to choose sources that are safe for the application method to avoid root or leaf burn.

In soils with low organic matter, sulfur supplementation is particularly important. Organic matter can contribute approximately 4 to 8 pounds of sulfur per acre for every 1% of content, but that release is often insufficient for high-yielding crops. Regular soil testing that includes sulfur helps ensure accurate nutrient management.

In addition to its role as a crop nutrient, sulfur can also be used as a soil amendment. It improves water infiltration, promotes better soil tilth, and assists in balancing excess cations like magnesium, calcium, or sodium. By displacing these elements, sulfur can enhance soil structure and support more efficient root development.

Sulfur Deficiency and Crop Impact

Sulfur deficiencies can be difficult to identify without proper testing, but visual symptoms often appear in new growth. Unlike nitrogen, which moves from older to younger leaves, sulfur is immobile in the plant. As a result, early signs of deficiency include yellowing in the newest leaves or, in the case of corn, the whorl. These symptoms indicate a disruption in chlorophyll production and protein synthesis, both of which are vital to crop health and grain quality.

Proper sulfur levels contribute to efficient photosynthesis, stronger plant structure, and improved grain protein content. In high pH or arid soils, where sulfur requirements are often elevated, regular monitoring and adjustment are especially important.

Enhancing Nitrogen Efficiency with Sulfur

Sulfur and nitrogen are closely linked in plant metabolism. Applying sulfur with nitrogen not only meets crop needs but also improves nitrogen uptake and internal movement. Sulfur acts as a natural stabilizer for nitrogen, reducing loss and enhancing efficiency. Many nitrogen fertilizers include sulfur for this reason, providing a more balanced nutrient supply.

By including sulfur in nitrogen applications, growers can support healthier, more productive plants while minimizing nutrient loss. This strategy helps maximize return on fertilizer investment and ensures the crop has what it needs throughout the growing season.