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  • Modern high-yielding corn hybrids and soybean varieties require large amounts of nitrogen late into the growing season for maximum yields.
  • Conventional nitrogen fertilizer sources applied at pre-plant timing can be subject to environmental losses under certain conditions.
  • Nitrogen loss increases the risk of falling short of late-season plant nitrogen requirements. 
  • Slow-release nitrogen fertilizers based on methylene urea provide an option to manage risk and ensure late-season nitrogen availability.
  • The FlexN™ lineup from GROWMARK provides several formulations of slow-release nitrogen.

Modern corn hybrids produce more plant biomass and greater yields, which require larger amounts of total nitrogen.  The majority of nitrogen uptake still occurs during the vegetative growth stage, and this accumulated nitrogen remobilizes into corn grain during grain-fill.  As yield potential has increased, the modern hybrids tend to acquire a higher proportion of their required nitrogen after flowering than in the past, by as much as 31%. 


Modern soybean varieties, coupled with the progressive use of insecticides and fungicides, have also resulted in larger biomass production and higher yield trends in recent years.  Many people fail to appreciate that total nutrient uptake in soybeans can actually exceed that of a corn crop.  The soybean plant acquires nutrients at the greatest rate during the reproductive stages between R2 (full bloom) and R5 (beginning seed formation).  The soybean seed is a more nutrient-dense sink than corn grain, requiring extensive mobilization of nutrients during pod fill.  As yields have increased with modern practices, the relative proportion of nutrients acquired during the pod fill stage has also increased, by an average of 18% for nitrogen.  Historically, growers relied exclusively on nitrogen-fixation nodules and mineralized nitrogen from soil organic matter to meet the soybean nitrogen needs, but supplemental fertilizer nitrogen now may be required to break through current ceilings into new yield territory.      

Clearly, having adequate nitrogen available for both corn and soybean plants during maximum uptake and grain fill periods is critically important for driving top-end yields.  The potential problem that growers face is the inherently leaky nature of the nitrogen cycle.  Conventional nitrogen fertilizers applied pre-plant may be subject to significant environmental losses under certain environmental conditions, which can limit the amount of nitrogen available to the plant during critical growth stages.  Several different solutions can help manage this risk, but one option is slow-release nitrogen.


Methylene urea, which is formed by a reaction of urea and formaldehyde, is an excellent form of uncoated slow-release nitrogen.  Methylene urea contains a combination of stable intermediate-chain-length urea polymers and 15-30% unreacted urea nitrogen.  The resulting product is a blend of immediately available nitrogen and slow-release nitrogen, the latter of which is made available over time through microbial activity and reactions with water.  The rate of conversion to available nitrogen depends on the rate of microbial activity and is driven by soil temperature, moisture, pH, and oxygen.  In a typical growing season, the slow-release fraction will be made available over a period of 8-12 weeks.  Optimal timing of application affords enough time for release and uptake by the crop.  The best timing for corn is early vegetative as a partial side-dress replacement or up to the late vegetative stage as a foliar application.  Optimal timing for soybeans is mid-vegetative to early pod stage. 

The FS System offers a full lineup of slow-release nitrogen products under the brand name FlexN™.  These products are clear liquids that can be applied via irrigation, aerial, and ground systems.  The products are generally compatible as a tank mix with other pesticides and bring a high level of crop safety when applied as a foliar.  Some formulations also include Boron, a nutrient associated with reproductive efficiency.  Please see your FS PARTNERS Crop Specialist to determine which FlexN™ product is right for your farm. Always read and follow label directions.

Image 1.  Nitrogen uptake and partitioning curve in corn yielding 230 bu/ac (Bender et al., 2013).
Image 2.  Nitrogen uptake and partitioning curve in soybeans.  Note: 1 kg/ha equals 0.89 lbs/ac, or 275 kg N/ha equals approximately 245 lbs N/ac.  (Adapted from Bender et al., 2015).

Modern Corn Hybrids' Nutrient Uptake Patterns. (Bender et al, 2013)
Nutrient Uptake, Partitioning, and Remobilization in Modern Soybean Varieties.  (Bender et al, 2015)

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