Not All Nitrogen Sources Are Created Equal: Insights from The Mill’s 2025 Crop Showcase

Timing and form of nitrogen application can make or break a corn crop. Even with a solid pre-plant program, the crop’s nitrogen needs evolve rapidly through vegetative growth and into reproduction. Managing in-season nitrogen isn’t just about how much you apply; it’s about what form of nitrogen you use and how efficiently it feeds the crop. 

At The Mill’s 2025 Crop Showcase, we examined how different nitrogen sources performed in a real-world topdress application, evaluating their impact on yield and nitrogen-use efficiency (NUE). 

The Objective: Comparing In-Season Nitrogen Sources in Corn 

This trial was designed to determine the effectiveness of a homogeneous nitrogen and sulfur fertilizer compared to a traditional Urea + AMS topdress. The study looked at whether a blended N+S source could maintain or improve yield potential while reducing cost and logistical challenges. 

Trial Design 

Field Trial 10: In-Season Nitrogen Source Study, The Mill 2025 Crop Showcase. 

Why Nitrogen Source Matters

Nitrogen is highly mobile in the soil, and its efficiency depends on both form and timing. At The Mill, we’ve tested and refined in-season nitrogen programs for more than a decade, learning that how nitrogen is delivered can make as much difference as how much is applied.

Urea + AMS

The Urea + AMS blend has been our go-to topdress source for roughly ten years, and for good reason. This combination offers readily available nitrogen along with a reliable source of sulfur, supporting crop color and chlorophyll production through critical growth stages.

While volatilization risk is a real concern with untreated urea, especially on hot, sunny days without rain in the forecast, we proactively manage this by pre-treating all urea in our bins with a nitrogen stabilizer. This extra step provides protection well beyond industry standards, ensuring that applied nitrogen stays where the crop can use it.

An additional advantage of the Urea + AMS system is flexibility. Because nitrogen and sulfur are applied as separate products, variable rate technology allows us to adjust each independently based on crop needs, soil zones, and yield potential. That adaptability has proven valuable for growers looking to fine-tune nutrient delivery within each field.

Homogeneous N+S Products

Homogeneous N+S fertilizers combine nitrogen and sulfur in every prill, creating a uniform nutrient blend that promotes even feeding and reduces the potential for striping. These products can simplify logistics and ensure consistent nutrient distribution across the field.

However, one drawback is that their nutrient ratio is fixed, for example, a 40-0-0-5.5S product always delivers that exact ratio per 100 lb of material. If an agronomist or grower determines that a field requires more or less sulfur relative to nitrogen, they must spike or blend another product to reach the desired N:S ratio.

Both systems have their place; the choice ultimately depends on management goals, equipment setup, and the level of precision a grower wants to achieve.