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February 18, 2022

Keys to Preventing Sulfur Deficiency in Cotton

Sulfur deficiency in North American crops has increased dramatically in the last several decades and cotton growers haven’t been spared the effects. And that’s a problem because sulfur is an essential component of amino acids methionine and cysteine, critical building blocks for protein formation in cotton plants. Sulfur is also an essential element in the creation of chlorophyll.

Low sulfur in cotton crops limits stock and boll development and makes optimal growth and yield impossible.

Why sulfur deficiency?

There are a few factors at play here. Legislated reductions in sulfur emissions from the industry have been good for the environment overall, but they’ve come at a price to many farmers. According to The Sulfur Institute, sulfur from industrial emissions decreased by 90 percent from 1990 to 2019. Producers can no longer count on 10 to 20 pounds per acre of sulfur from yearly rainfall.

Sandy soils often have low levels of sulfur. This is an issue in Coastal Plains soils. Sandy soils tend to lose nutrients easily. Leaching occurs in periods of heavy or prolonged rainfall. This is a particular concern when using a sulfate-sulfur, such as AMS. Those who grow cotton under irrigation have become pretty dialed-in on strategies for preventing leaching.

Increased use of sulfur-free pesticides and widespread use of fertilizers that contain little or no sulfur further contribute to sulfur deficiency in soils. And all this comes at a time when higher-yielding cotton crops require more sulfur.

Symptoms of sulfur deficiency

Look for uniform yellow coloration, known as chlorosis, in new growth near the top of plants – severe sulfur deficiency can cause the entire plant to turn yellow. Stunted growth is another sign of low sulfur.

Low nitrogen, on the other hand, typically shows up as yellowing of the bottom leaves. Soil and tissue sampling can confirm – or put to rest – any suspicions.

Meeting season-long sulfur needs

Cotton typically needs 10 to 25 pounds of sulfur per acre for optimal lint production. Higher yields typically warrant higher input levels. So how do you safely and economically meet the demand?

In determining rates, you’ll want to maintain a proper nitrogen-to-sulfur ratio (N:S) of 12:1 to 15:1. This will optimize nitrogen utilization. Having too much nitrogen and too little sulfur can result in reduced yield

Can cotton growers rely exclusively on elemental sulfur?

Cotton crops require sulfur season long. Sulfur is in high demand from the first square to the first bloom, with peak demand coming at the fourth week of bloom.

Elemental sulfur has proven to be a good choice for cotton growers due to its high analysis (85-90% S) of season-long sulfur and minimal loss from leaching compared to sulfate fertilizers. It’s a steady and predictable source of sulfur.

Those concerned with leaching often wonder if it is possible to transition away from AMS and move exclusively to an elemental sulfur product instead.

Elemental sulfur can be managed quite easily to provide sulfate-sulfur at the time of crop demand, and throughout the cropping season. When elemental sulfur is first introduced to sulfur deficient soils, some AMS is advised to ensure sulfate-sulfur is available in critical early growth stages. This is a strategy that has been used with great success by canola growers in Canada when transitioning to exclusive elemental sulfur use.

Because of the high analysis, degradable elemental sulfur can be applied at low rates – and will have a minimal effect on soil pH. But be cautious when using a sulfate product as a foliar rescue treatment. It can cause leaves to burn.

If supplementing isn’t economical, consider applying the full rate of elemental sulfur at planting to ensure a good supply of available sulfur is when plants begin leafing out, setting squares, or starting to fill bolls.

Plan for your sulfur needs

Sulfur no longer falls free from the sky. Yet it remains an essential macronutrient that’s needed to optimize cotton production and maximize yield potential.

Including ample elemental sulfur as part of a well-considered crop nutrition plan is the best way to prevent sulfur deficiency in your cotton crop and help tilt the tables toward a bountiful harvest.

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