Sulfur Management

The same year that Earth Day began, the Clean Air Act came into effect. The impact the Clean Air Act had on air pollution was enormous; with decreases in air pollutants – specifically, the sulfur dioxide emissions from coal burning facilities. This lead to a decrease in acid rain, which in turn, decreased the amount of atmospheric sulfur available for plant uptake.

Sulfur has become the fourth major plant nutrient for crop production. Sulfur (S) in the plant increases nitrogen (N) efficiency, increases protein in forage and grain, boosts yield, helps develop enzymes and vitamins, promotes N fixation in legumes, aids in seed production, controls nitrate build up in plants, and is necessary in the formation process of chlorophyll. There is a strong relationship between Nitrogen and Sulfur in the plant ratios – varying between N/S 15/1 – 7/1. When fertilizing with N, the addition of S will increase N Use Efficiency. The addition of S to N fertility has an environmental effect of reducing nitrate leaching potential.

The soil organic matter contains the largest amount of the soils S. For this S to be converted to the plant available Sulfate (SO4), bacterial oxidation must occur. The sulfate form is soluble, moves through the soil with the soil water, and is readily leached under high rainfall events. Soil texture will affect S opportunity. Sandy soils present the biggest challenge maintaining high organic matter (OM) levels and their high leaching potential.

The intensification of agriculture with improved crop varieties pushing higher yield potentials, improved air quality, low sulfur fuels, and sulfur free plant protection materials have increased the need for the addition of sulfur in crop production. Increasing organic materials in the soil by using animal wastes and cover crops will help stabilize soil S. Along with the addition of S through the growing season, paying close attention to high protein crops and crops using large amounts of N is important in sulfur management.

Measuring S in crop production systems is challenging. Testing for OM levels through soil testing, knowledge of cropping systems, and tissue analysis will provide some of the best indicators. Forage samples may also give some insight into S use by the crops  by observing % protein and S containing amino acids. The soil test for S without additional information may be misleading depending on time of year the sample is taken and the soil temperature.

Again, it is best to look at other soil and crop needs before choosing a source, but S can be added to fertility programs with several products.   Crop type, soil information, and yield goals should be used to determine crop needs and sources.

Ammonium Sulfate will supply readily available S along with N

K-Mag or SPM will provide S, Potassium (K), and Magnesium (Mg)

Ammonium Thiosulfate (ATS) with UAN liquids

Gypsum, which is Calcium Sulfate, will provide Calcium if needed

MgSo4, or Epsom Salt, can provide Mg and be used as a foliar

Sulfate of Potash can provide a low salt source of K along with S

Take a look at the attached newsletter for more information on Earth Day, Sulfur, or Spreader Calibration.

CaroVail Newsletter 04202018