Release Factors
Release Factors

Release Factors

Factors Affecting Enhanced Efficiency Fertilizer Nutrient Release

For any fertilizer—including enhanced efficiency fertilizers (EEFs)—these environmental factors contribute to how and when each releases nutrients, and the rate of that release.

In water soluble or quick-release fertilizers such as urea and ammonium nitrate, water dissolves the source and nutrient release is immediate. Although turfgrass response is rapid with these fertilizers, too much water makes nitrogen (N) prone to leaching and runoff.

Stabilized nitrogen is based on urea, so water is important in solubilizing the fertilizer. The presence of inhibitors retains N in plant-available forms longer than non-amended urea though, making the N less prone to loss.

In controlled-release and slow-release fertilizers, water is utilized to dissolve the nutrient inside the granules. Although it does serve as an activator, water may impact the release rate of sulfur-coated products, but does not impact the rate for polymer-coated fertilizers.

Both ambient and soil temperature can affect the release of nutrients to the plant. High temperatures can also increase the potential for ammonia volatilization.

In the case of controlled-release fertilizers, temperature impacts the rate of diffusion, the primary control on nutrient release. Controlled-release fertilizer release rates therefore increase with rising temperatures, and vice versa.

Microbial Activity
Soil microorganisms also impact how and when some EEFs release. Methylene urea (MU) and urea-formaldehyde (UF) fertilizers, as well as natural organics, rely on microbes to break down the fertilizer, releasing nutrients through mineralization.

Microbes can also degrade the coatings of sulfur-coated fertilizers, enabling nutrient release. Microbial activity is generally higher in warmer soil temperatures and less active in colder conditions, so temperature impacts the release rates of these EEFs.