Some Thoughts on Sulfur for Turfgrass

Some Thoughts on Sulfur for Turfgrass

turfgrass managementSulfur is one of those elements that seems simple enough, but I often have conversations about it. Some clients worry about too much, some clients want more. There are a couple of “lanes” people choose on sulfur and once they are in the lane it is hard to get out! I hope this summary on sulfur will help clarify some misconceptions.


With many places that I work, the soils are high pH and often calcareous. I have seen sulfur on soils tests that are so high, you would think it was a sample from a bag of elemental sulfur. Take a look and as I see you in the upcoming weeks, we will have something to chat about.

4 Comments on Sulfur from Brookside Labs

Sulfur is a highly reactive chemical element, in fact, it readily reacts with most known elements, save for the noble gases. It even has a bit of the Midas Touch and will surprisingly react with the usually inert gold! Sulfur usually exists in nature as sulfide (S2- ) and sulfate (SO4 2- ) minerals or bound within soil organic matter, though it is sometimes found in its elemental (S) form. Most sulfur in commercial use today is derived from cleaning the contaminants from hydrocarbon energy sources. The elemental form is most often derived from natural gas and petroleum processing and the gypsum form from coal.

Sulfur in Plants

Sulfur is almost exclusively taken up by plant roots in the sulfate form. I say ‘almost,’ because there can be some sulfur dioxide (SO2) gas absorbed by the leaf. Once sulfate is taken in by the plant, it is reduced into sulfite and then sulfide before being assimilated into the amino acids: cysteine, cystine, and methionine and the vitamins: biotin, thiamine, and B1. Other vital roles S serves in plants is related to the oxidation of fatty acids and intermediates in the citric acid cycle.

Sulfur on average, constitutes around 0.15 – 0.45 % total dry tissue in healthy plants, or approximately 1/10th that of nitrogen, though this value can be as high a 1% in some plants. Sulfur deficiency often presents as slow growth and maturity of leaves. These plants may also appear spindly and have thin stems. Yellowing and pale green leaves are typical, which can look similar to N deficiency. Furthermore, plants suffering from S deficiency can struggle with protein production leading to accumulation of nitrate (NO3 ) in the tissue negatively impacting quality and plant health. Sulfur is particularly important to the legume, cabbage, and onion families.

Sulfur in Soil

Sulfur in the soil can be in several forms including sulfate in the soil solution, sulfate adsorbed on minerals, sulfate minerals, and sulfur within soil organic matter. Sulfur cycling is somewhat similar to that of nitrogen in that there is a gaseous phase and it is firmly connected to the soil organic matter. Deficiencies are most likely to be found in sandy soils with low levels of organic matter.

Solution SO4 2- : Sulfate in soil solution is immediately available for plant uptake and plants generally rely on mass flow, though some diffusion also takes place. Large seasonal fluctuations of availability are related to weather impacts on mineralization rates and leaching. As a general rule of thumb, I have seen suggestions that SO4 2- leaches at about half the rate of NO3 . The leaching of SO4 2- has also been shown to be more prominent when single charge cations (K+ and Na+) are predominant. Leaching tends to be the least from acidic soils with substantial exchangeable Al3+.

Adsorbed SO4 2- : Sulfate adsorption can be significant in highly weathered soils containing high levels of iron and aluminum or kaolinitic clay. Adsorption also tends to be more prevalent in the lower horizons of the subsoil. Which also makes sense, when we think about the tendencies of sulfate to move down through the soil profile. Organic matter can also adsorb sulfate under certain conditions. Adsorbed sulfate has been shown to be desorbed by phosphate. Conversely, phosphate has not been shown to be desorbed by sulfate. The take-home of this point – adding SO4 2- will not release plant available P.

Sulfate Minerals: Though sulfate may form precipitated complexes with Ca, Mg (Epsom salt), and Na (Glauber’s salt), many of these are so highly soluble that they are not commonly found in the solid-phase in soils. Only solid CaSO4 (mineral gypsum) is really commonly found in nature. Calcium sulfate can also occur as an impurity of calcium carbonate and is an important fraction in calcareous soils. This is something to keep in mind when interpreting soil test results. This S in not plant available but may be extracted and represented on a soil report.

Organic S: Sulfur contained within organic matter can represent 90 – 98% of the surface S pool in humid and sub-humid climates. On average SOM contains 0.5% sulfur. So, a “typi*cal” silt loam soil containing 3% SOM has about 30 lbs of organic sulfur in the surface 6 inches. Therefore, sulfur mineralization rate and timing should be an important consideration in a nutrient management context. Some estimates suggest mineralization rates between 5 – 15 lbs SO4 2- per acre per year. The release of organic sulfur into the plant available pool is controlled by similar factors that control nitrogen mineralization. Such as temperature, moisture, aeration, and pH. With sulfur mineralization being negligible below 50° F and increasing along with temperatures. Also similar to nitrogen, there seems to be a burst of sulfur mineralization following wetting and drying events. The window of critical C:S ratios that dictate sulfur mineralization/immobilization is much larger than that of C:N. I’ve seen critical C:N ratios from 15:1 – 25:1, however, the range of values for C:S ratios stretches from 200:1 – 400:1.*

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*4 Comments on Sulfur written by Chris Eidson, Agronomist