DOUGLAS AMARAL
TIFTON, GEORGIA
Sulfur (S) has quietly become one of the most important secondary nutrients in Georgia cotton production. Twenty or thirty years ago, sulfur deficiencies in cotton were relatively uncommon because growers received a steady supply of sulfur from atmospheric deposition through rainfall. Today, that is no longer the case. Improvements in air quality and reductions in industrial sulfur emissions have significantly decreased sulfur deposition across the southeastern United States. While this has been a major environmental success, it has also removed a nutrient source many cropping systems once relied upon. Combined with higher yielding cotton varieties and the predominance of sandy Coastal Plain soils, sulfur deficiency has become increasingly common in Georgia cotton production.
Sulfur plays a critical role in cotton growth and development. Without adequate sulfur, cotton cannot fully utilize applied nitrogen, regardless of how much nitrogen fertilizer is supplied. In many cases, growers may think they are dealing with a nitrogen problem when sulfur is actually the limiting factor.
Research across the Southeast, including work from University of Georgia and neighboring land- grant universities, consistently shows that cotton generally requires between 15 and 25 pounds of sulfur per acre to maximize lint production. On coarse-textured sandy soils, particularly under irrigation or in seasons with frequent rainfall, sulfur losses through leaching can become significant. In these situations, sulfur applications become even more important because sulfate- sulfur, the plant-available form, behaves similarly to nitrate in the soil and moves readily with water.
This issue is especially relevant in Georgia because many cotton acres are grown on soils with low organic matter and limited nutrient-holding capacity. Organic matter serves as a reservoir for sulfur and slowly releases sulfate as it decomposes. However, many Georgia Coastal Plain soils contain less than 1% organic matter, limiting their ability to supply sulfur naturally throughout the season. Heavy rainfall events, common during Georgia summers, can quickly move sulfate below the root zone, particularly in deep sands.
Sulfur deficiency often appears early in the season, commonly around first square or early bloom. One of the classic symptoms is a uniform yellowing of younger leaves near the top of the canopy. In severe cases, plants may appear pale green to yellow across the upper canopy, with reduced vigor and stunted growth. Reddish stems may also develop under prolonged deficiency. Because sulfur is relatively immobile within the plant, deficiency symptoms first appear in new growth. This is one of the key differences between sulfur and nitrogen deficiency.
Nitrogen deficiency typically shows up in older, lower leaves first because nitrogen can move from older tissue into newer growth when supplies are limited. Distinguishing between the two is important because applying additional nitrogen will not correct a sulfur deficiency and may actually worsen the imbalance between nitrogen and sulfur within the plant.
One of the best tools for diagnosing sulfur issues is tissue testing. Leaf tissue analysis can help confirm hidden deficiencies and evaluate the nitrogen-to-sulfur ratio within the plant. Research suggests that maintaining a nitrogen-to-sulfur ratio between approximately 12:1 and 15:1 supports efficient nitrogen utilization and optimum cotton growth. When the ratio climbs above 18:1 or 20:1, sulfur deficiency becomes increasingly likely. In these situations, additional sulfur applications may improve both nutrient efficiency and yield potential.
From a management standpoint, sulfur should be treated as a routine component of Georgia cotton fertility programs, especially on sandy soils. Preplant applications are generally preferred because they help ensure sulfur is available early in the season during rapid vegetative growth and square development. However, sulfur applied preplant on sandy soils can still be vulnerable to leaching if excessive rainfall occurs.
If sulfur was not applied preplant, including sulfur with sidedress nitrogen applications becomes extremely important. Ammonium sulfate is one of the most effective and commonly used sulfur fertilizers because it provides readily available sulfate-sulfur while also contributing nitrogen. Magnesium sulfate and ammonium thiosulfate can also be effective sulfur sources. Gypsum supplies sulfur as calcium sulfate and may fit well where additional calcium is also desired.
Elemental sulfur is another option, but it behaves differently from sulfate-containing fertilizers. Elemental sulfur must first be converted by soil microorganisms into sulfate before plants can use it. This conversion takes time and depends heavily on soil temperature and moisture conditions. Because of this, elemental sulfur is best suited for preplant applications rather than in-season rescue treatments.
While sulfur fertilization is important, growers should also think long term about improving soil health and nutrient retention. Conservation practices such as cover cropping, reduced tillage, and increasing organic matter can help improve sulfur cycling and reduce leaching losses over time. Fields with greater organic matter generally hold sulfur more effectively and provide a more stable nutrient supply throughout the growing season.
Ultimately, sulfur management in Georgia cotton is becoming less of an optional consideration and more of a foundational fertility practice. Modern cotton production systems demand high nutrient efficiency, and sulfur plays a direct role in supporting that efficiency. On Georgia’s sandy Coastal Plain soils, particularly under irrigation or in high rainfall environments, sulfur deficiencies can develop quickly and reduce yield potential before visual symptoms become obvious.
For most Georgia cotton growers, maintaining a consistent sulfur program that includes 15 to 25 pounds of sulfur per acre, combined with tissue testing and sound nitrogen management, will go a long way toward protecting lint yield and improving overall nutrient use efficiency. ∆
DOUGLAS AMARAL
UNIVERSITY OF GEORGIA