Sulfur

The article below has been reprinted from 2016. The importance of Sulfur has not diminished over the last year, nor will it in the coming years. The reduction of atmospheric deposition (acid rain) in the Northeast has greatly reduced the amount of S in the soil. That fact, combined with the increased demand for efficient use of N (the level of S in the soil is critical in ensuring efficient use of available N), means that monitoring S levels is an activity that is here to stay. The information below remains very relevant.
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, boost yields, helps to 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 N and S in the plant. Ratios vary between N/S 15/1-7/1, but whatever the relationship when fertilizing with N the addition of S will increase N use efficiency. The addition of S to the N fertility has a side environmental effect, reducing nitrate leaching potential.

The soil organic matter contains the largest amount of the soil’s S. For this S to be converted to the plant as available Sulfate (SO4), bacterial oxidation must occur. The sulfate forms are soluble and move through the soil with the soil water and are readily leached under high rainfall events. Soil texture will affect S opportunity. Sandy soils present the biggest challenge both in 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 (see attached map for variances in sulfate deposition), low sulfur fuels, and sulfur free plant protection materials have increase 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. Supplement animal wastes and cover crops with additional S through the growing season while also paying close attention to high protein crops and crops using large amounts of N.

Measuring S in the crop production systems is challenging. Testing for OM levels through soil testing can provide helpful 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 observing % protein and S containing amino acids. The soil test for S without additional information may be misleading depending on time of year that the sample is taken and by the soil temperature. S can be added to fertility programs with several products. Again it is best to look at other soil and crop needs before choosing a source. 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 is another liquid source. Gypsum, which is Calcium Sulfate, will provide Calcium if needed. Epsom salt or MgSo4 can provide Mg and be used as a foliar. Also, Sulfate of Potash can provide a low salt source of K along with the S. These are just a sampling of the potential sources of S. Crop type, soil information, and yield goals should be used to determine needs and identify the appropriate source.

By Frank Flis