JOE KNOWS! Sulfur's Role in Turf & Soil HealthDecember 20, 2017
Why Sulfur's Presence in Soil is Crucial to a Sustainable Turf
by Joe Marchinchin, Agronomist, R&D, Turf Care Supply Corp.
Often thought of as the 4th “primary” or “macronutrient,” sulfur plays an essential role in maintaining healthy turf. Two of the twenty amino acids made by plants (methionine and cysteine) contain sulfur, as do countless proteins that catalyze reactions inside plant cells. Sulfur is also a component of many vitamins that helps the plant defend itself against various abiotic stresses. Without sulfur, plant life (and all life), would not be possible.
Sulfur’s Role in Soil
Sulfur serves as an important soil conditioner. Normally mobile in saturated soils, sulfur helps to reduce sodium uptake in plants. Much like the nitrogen cycle, sulfur follows a similar pathway. Sulfur is only available for plant uptake in its inorganic form, SO4-2 (sulfate sulfur). Accordingly, much as nitrogen fertilizers are subject to volatilization, sulfur can also volatize in the form of H2S (hydrogen sulfide.) Ammonium sulfate [(NH4)2SO4 - the most economically practical sulfur-based fertilizer] is also a great compound for reducing the pH of alkaline soils. Although it is commonly accepted that sulfur lowers soil pH, it’s actually the ammonium component that forms a mild acid after disassociating from a sulfate ion. In the case of adding ammonium sulfate to alkaline soils, the sulfur just comes along for the ride.
Sulfur Deficiencies in Turf – What to Look for
Unfortunately, nitrogen and sulfur deficiency symptoms often mimic each other, so it can be difficult to discern the two. In general, turf suffering from a sulfur deficiency exhibits light-green/yellowing blades. Lack of sulfur may also result in decreased turf growth rate. Sandy soils tend to suffer from low-sulfur content more so than organic rich soils due to sulfur’s relatively high leaching potential. Because sulfur is immobile in plant tissues, once it becomes depleted in the soil, newly developing leaves are the first to show deficiency symptoms.
Of all the different forms of sulfur fertilizers and soil amendments available on the market, ammonium sulfate is by far the most popular. In addition to providing turf with a strong nitrogen component and helping to mitigate pH shifts, ammonium sulfate is used an adjuvant to increase the efficacy of herbicides, insecticides, and fungicides.
When and How to Apply Sulfur
While elemental sulfur (88% pure) is occasionally used to decrease soil pH, most applicators prefer ammonium sulfate. If using ammonium sulfate or any other sulfur-based fertilizer or soil amendment, perform a soil pH test first, then follow the application instructions on the label. Applying too much ammonium sulfate can burn your lawn. Once applied, wait at least 60 days before performing another soil test to determine if more ammonium sulfate should be added. Ammonium sulfate is most effective and safest on turf when applied in the spring, then summer if conditions warrant an additional application. Avoid fall applications due to increased risk of disease and dead patches. Ammonium sulfate is non-flammable and does not clump under high-humidity, making it easy to store and use across multiple seasons.