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Topdressing SO4 + Urea on Corn

by | Jun 17, 2019 | Ag

Whether you’re responding to nutrient deficiencies or topdressing as planned, applying a blend of urea and SO4 post-emergence is a practice many of our dealers are taking advantage of.

In a cool, wet year, topdressing nitrogen and sulfur helps ensure nutrients are available when the plant needs them. With corn growth stages ranging from not yet planted to V5 across our trade territory, the window to topdress will be wider than normal.

The Do’s and Don’ts
If you’re interested in topdressing a urea and SO4 blend, here are the do’s and don’ts.


  • Apply at growth stages V4 to V7.
  • Apply a rate of SO4 in the range of 100-200 lbs/A.


  • Over-apply nitrogen stabilizer volumes. Excess moisture can cause SO4 pellets to breakdown and result in gumming or buildup on blending and/or application equipment.
  • Let the blend sit over-night.

Why switch topdress sulfur from AMS to SO4?
If you’re already topdressing AMS, you may want to consider the benefits of SO4.

SO4 has a strong and steady sulfur release. AMS is 300x more soluble that SO4 and more prone to leaching. You can count on the sulfur from SO4 being plant available throughout the growing season.

An SO4 and urea blend has less burn potential than AMS. Fertilizers with a high salt index are more prone to burn plants and replacing AMS with SO4 will reduce the overall burn potential of the blend. Click here for more details on salt index.

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