Top-dress/Side-dress Sulfur in corn and soybeans

Sulfur is a vital nutrient for high-yielding crops.  I call it the fourth major element.  To understand why sulfur is needed in a top-dress/side-dress application, we first need to know why it is important to the plant, what is the best timing of application, and what fertilizer products to use.

Why is Sulfur so important?

• Leguminous plants such as soybeans and peas will fix nitrogen more efficiently.
• Help produce grain by increasing oil and protein content. 
• Chlorophyll formation is produced by an enzyme that sulfur plays a big role in producing. 
• Improves winter hardiness by enhancing root growth and vigor. 
• Is in every living cell to synthesize amino acids and proteins.

Timing?

The timing of nutrient uptake within the plant may require multiple applications, sulfur is no exception.  Sulfur deficiency is visually more evident in new growth when corn is around V5 and soybeans around V3.  But more than 50% of the crop’s sulfur uptake occurs after the R1 stage in both corn and soybeans. Sulfur is a great partner to nitrogen and helps corn metabolize it more efficiently.  So, apply sulfur when nitrogen is applied to your corn crop.  Just like with nitrogen we need to ensure that there is an ample amount of sulfur available for the plant during the R stages of the plant’s development.  Top-dress or side-dress applications from V4-V7 will help push out nutrient availability during the R stages.  Fertigation is also a great option before VT.

Sources of Sulfur?

Ammonium sulfate (AMS) is made up of nitrogen and sulfur with a guaranteed analysis of 21-0-0-24.  It is a great source to be applied pre-plant through V7.  Ammonium thiosulfate (ATS) is made up of nitrogen and sulfur with a guaranteed analysis of 12-0-0-26. It is a great source to be applied pre-emerge through VT.  Gypsum (SO4) is made up of soluble calcium and sulfate sulfur with a guaranteed analysis of 0-0-0-21Ca-17S.  It is a great source to be applied pre-plant through V7 and in soybeans because of the lack of nitrogen in its analysis.  There are also many nutrient packs for foliar applications that work well to spoon-feed the plant.

Summary:

Sulfur is an important part of the plant’s internal workings from fixing nitrogen to chlorophyll to photosynthesis.  Topdressing/Side-dressing sulfur with nitrogen applications in corn pushes the availability past R1 when most of the sulfur is used.  One of the ways sulfur helps increase yield is by increasing oil and protein in the grain.  Sulfur comes in many different forms to fit your crop type needs and application timings.

Sources

• Calcium Products 98G for topdressing application by Glen Howell
• Mosaic, nutrient knowledge, sulfur