Topdress for Your Crops’ Bottom Line

Whether it's corn or soybeans, fertilizing is essential for a successful harvest, and topdressing helps growers deliver timely nitrogen and sulfur during the growing season.

The recent heavy rainfall in parts of the country has likely led to nitrogen and sulfur losses below the root zone, as well as nitrogen loss as gas from ponded areas. Growers may see their corn leaves yellowing, and soybean crops could be negatively impacted.

Topdressing with ammonium sulfate fertilizer can be effectively used as a rescue treatment. Blends of urea and ammonium sulfate fertilizer once a corn field is fit can make a difference at harvest time, and simply topdressing with ammonium sulfate fertilizer for soybeans is a proven solution.

Read below to learn why topdressing with ammonium sulfate fertilizer is the right way to give your crops a much-needed boost.

Tailorable to the Crop and Growth Stage

As with most things in farming, timing is everything, and it's important to gauge the "when" by looking at the plant stage and field conditions rather than a calendar date.

For corn: Even if some sulfur was applied to your corn crop pre-plant (alongside phosphorus and potassium), ammonium sulfate fertilizer is recommended as a topdress with urea (or stabilized urea). It's preferable that this topdress take place by the V6 growth stage and no later than V8 for maximum benefit. By doing so, these nutrients will not be limiting factors during the following high-demand growth stages.

For soybeans: Topdressing should preferably occur by the V4 growth stage (four fully unfolded trifoliate leaves) to ensure sufficient sulfur for nodulation (the process that secures free atmospheric nitrogen for the soybean crop).

No Need for Mechanical Incorporation

Ammonium sulfate fertilizer resists volatilization loss due to its non-volatile nature in neutral and acidic soils. Simply spread the ammonium sulfate fertilizer over the field and let the rain do the rest. If possible, time your application right before a light rain shower, as the granules readily dissolve in water, delivering immediately available nitrogen and sulfur to the crops' roots.

Fun fact: Compared with other nitrogen sources, ammonium sulfate fertilizer has been shown to be less prone to leaching and denitrification losses.

The Business Case

Growers have long used ammonium sulfate for topdressing corn with demonstrated benefits. However, topdressing soybeans with ammonium sulfate fertilizer is a more recent practice, prompted by reduced atmospheric sulfur depositions from air quality regulations and earlier planting dates, both of which result in less sulfur available at crop establishment.

Independent crop consultant Missy Bauer of B&M Crop Consulting recently added important context to this conversation by sharing the results of a three-year field trial comparing soybean crops with topdressing of ammonium sulfate to those without it.

Based on observations, ammonium sulfate fertilizer increased branching and pod counts and produced larger, darker leaves.

But the evidence goes beyond observation-the numbers add up, too.

When you break it down, ammonium sulfate fertilizer costs about $30-40 per acre. In Bauer's trials, the average soybean yield response to ammonium sulfate fertilizer topdressing was 4.7 bushels per acre. At the soybean price of $10.70 per bushel, that extra yield brings in about $50.30 per acre. After accounting for application costs, this leaves a net return of roughly $10 per acre.

Therefore, Bauer concludes, "…the cost of applying ammonium sulfate is worth the investment. It's evident from the yields, the soil and the numbers-even if you run them conservatively."

Boost in Nutrients Equals a Boost in Yields

Whether you grow corn or soybeans, this second application gives you an undeniable edge, and ammonium sulfate fertilizer delivers immediate sulfur and nitrogen exactly when crops demand them most to maximize grain-fill.

Want the Sulf-N® ammonium sulfate advantage this season? Contact your AdvanSix sales representative or visit soybeans.advansix.com.