Update from the Field: Where Have All the Sulfates Gone?
Posted by Dave Dyson, Agronomist on January 22, 2019
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When Peter, Paul, and Mary sing “Where Have All the Flowers Gone?”, I think of all the sulfate that used to be in the soil. In the past, atmospheric deposition of sulfur from the burning of high-sulfur coal and diesel provided enough sulfur to satisfy crop needs. Pollution controls and conversion of power plants from coal to natural gas have greatly reduced sulfur deposition, increasing the possibility of sulfur deficiency in crops. I continue to see an increasing amount of sulfur deficiency in corn, soybeans, wheat, and alfalfa every year around the Cornbelt. Sulfur is immobile in the plant, meaning deficiency symptoms will appear on younger leaves. Visual symptoms of sulfur deficiency in corn include striping or yellowing of corn leaves. In soybeans, the deficiency appears as overall yellowing of leaves. (Figure 1)
Figure 1: Sulfur deficiency visual symptoms in corn and soybeans
In the past, the solution to our sulfur needs was literally “Blowin’ in the Wind”. With the pollution source of sulfur all but cleaned up, we now have to rely on organic matter to release a free source of sulfur. According to Purdue University, in 2001, areas of Indiana received as much as 18 pounds per acre of sulfur from atmospheric deposition. In 2015, sulfur deposition was less than 10 pounds per acre in much of Indiana (Figure 2). Each percent of organic matter your soil contains in the plow layer will yield about 100 pounds of sulfur per acre, according to Dr. Jim Camberato at Purdue. This sounds great until you realize the organic sulfur must be mineralized to sulfate to be taken up by the crop. At most, only a small percentage of the organic sulfur is made available to the crop annually.
Figure 2: Total atmospheric deposition of sulfur in 2001 compared to 2015.
Only a few pounds of organic sulfur is available to the crop every year, and the research of Dr. Shaun Casteel (Purdue University College of Agronomy) has shown we need at least 20 pounds of sulfate prior to planting to reach our optimum yield. So how do we make up the balance? The answer, my friend, is not “blowin’ in the wind”; the answer is applying NutraSoft® DG pelletized gypsum.
NutraSoft DG pelletized gypsum is made with mined gypsum that is ground to a flour-like powder, then granulated into fertilizer-sized granules. These granules will disperse on contact with moisture and release calcium and sulfur into the soil. If we apply 125 pounds per acre of NutraSoft DG right before planting, we will achieve the 20 pounds of sulfate for this year’s crop. We will not achieve this by applying elemental sulfur prior to planting.
Elemental sulfur (SO2) has the same plant uptake issue as organic sulfur; it has to be oxidized by the soil to the sulfate form before the plant can utilize it. Warm temperatures, good moisture, and aeration are required for sulfur oxidizing bacteria to function. Sulfur oxidation is minimal at soil temperatures between 50° F and 75° F, so peak rates of sulfur oxidation do not occur until late spring to early summer.
In conclusion, we are seeing more and more acres suffering from sulfur deficiency every spring. Whether the cause is the lack of atmospheric sulfur being deposited to the soil or low organic matter supplying the needed sulfate to the crops, the solution is to apply 20 pounds of sulfate prior to planting. NutraSoft DG pelletized gypsum will not only supply that sulfate to the crops but also help build calcium in the soil, while not distorting the pH.
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Dave Dyson is a regional agronomist for The Andersons’ Farm Centers which are located throughout Ohio, Michigan, and Indiana. He is an Indiana native and grew up on a dairy farm in Miami County. A graduate of Purdue University with a degree in Crop & Soil Science, Dave has a deep knowledge of various agronomic topics and is committed to helping growers improve their crops. If you have any questions, Dave can be reached at david_dyson@andersonsinc.com.
NutraSoft is a registered trademark of The Andersons, Inc.
