SULFUR: THE HIDDEN HERO OF HEALTHY CROPS
Growers, in many areas, have recently been considering adding sulfur nutrition to their fertilizer program.
Sulfur (S) is an essential nutrient for plant growth and development, playing a crucial role in various physiological and biochemical processes. Despite its importance, sulfur is often overlooked compared to other macronutrients like nitrogen (N), phosphorus (P), and potassium (K). However, changes in environmental conditions and agriculture practices have highlighted the increasing need for sulfur supplementation.
“Growers for a long time never had to worry about sulfur nutrition,” says Dr. Karl Wyant, director of agronomy for Nutrien. “It came from the air until pollution controls were put in place, which cut the amount of ‘free’ sulfur available. In some areas of the Eastern Corn Belt, the ‘free’ sulfur was cut from around 30 pounds per acre in 1990 to often less than ten pounds per acre by 2015.” The crop sulfur supply, as a result, is now being supplied by added fertilizers and manures.
Consequences of Sulfur Deficiency
Sulfur deficiency in crops can significantly impact agricultural productivity and crop quality. Common symptoms of sulfur deficiency include yellowing of young leaves, stunted growth, and delayed maturity. These symptoms can often be confused with nitrogen deficiency, but they usually appear first on the younger leaves (top of the plant) when caused by a lack of sulfur.
The consequences of sulfur deficiency extend beyond reduced crop yield. Crop nutritional quality can also be affected, as sulfur is involved in synthesizing amino acids and proteins. Lower protein content in crops can affect human and animal nutrition. Additionally, sulfur deficiency can impair a plant’s ability to withstand environmental stresses and pathogen attacks, leading to increased susceptibility to diseases and poor resilience under adverse conditions.
Addressing Sulfur Deficiency
Assessing soil sulfur levels through soil testing and plant tissue analysis is crucial to addressing sulfur deficiency in crops. If deficiency is detected or anticipated, sulfur can be supplied through various means, including:
Application of Sulfur-Containing Fertilizers:
Fertilizers like ammonium sulfate, potassium sulfate, thiosulfate, and elemental sulfur can be used to replenish soil sulfur levels. You can apply and incorporate the elemental sulfur form for fall fertilizer applications because it won’t leach down into the soil with rainfall or snowmelt and will be available to the plant in the spring when the soil warms up and the microbes start to transform the sulfur into plant sulfate. You can also apply the elemental sulfur form early on in the spring.
Use of Organic Amendments: Organic matter, such as compost or manure, can help increase soil sulfur content.
Foliar Application: In some cases, sulfur can be applied directly to plant leaves as a foliar spray.
However, Wyant stresses that growers need to develop a strategy for when and in what form to apply sulfur.
“You can’t just throw sulfur out,” he says. “You need to decide when to put out your sulfur relative to when the crop will need it. You will want to incorporate the elemental sulfur form for fall fertilizer applications because it won’t leach down into the soil with rainfall or snowmelt and will be available to the plant in the spring when the soil warms up.”
Wyant adds that micronized sulfur technology (MST) ensures that sulfur resists overwinter and early spring leaching losses. This is due to low activity of microbes and the reduced speed of conversion (sulfur to sulfate) in cold soils. In certain geographies, a fall application of Smart Nutrition MAP+MST in cooler weather conditions will allow sulfur to stay in the soil until it is warm enough to become available in the sulfate form.
For more immediate sulfur problems, Wyant recommends using the sulfate form to address the deficiency as the plants can readily use this form upon application. Elemental sulfur and thiosulfates will need to be converted by microbes to sulfate before the crop can use it. This “time delay” can be used strategically to resist leaching and runoff losses of applied fertilizer.
Sulfur is a critical yet often overlooked nutrient in crop production. Understanding the symptoms and consequences of sulfur deficiency and implementing appropriate fertilization strategies is essential for maintaining crop quality and productivity. By carefully planning sulfur applications, choosing the right forms, and timing, growers can effectively address sulfur deficiencies and ensure that their crops receive this essential nutrient when they need it most.