Slow Release Nitrogen Comparisons Between Greenview® and Scotts®

Agronomist – Lebanon Seaboard Corporation

Nitrogen fertilizer in lawn nutrition

Nitrogen is considered to be the most important nutrient in turfgrass nutrition. Although many other nutrients are essential for healthy turf, nitrogen is used by turgrass in larger quantities and is therefore more often a limiting factor in turfgrass growth and appearance. The vast majority of nitrogen used by the grass plant is absorbed by the root system and moved through the vascular system of the plant to various sites of metabolic activity. Nitrogen affects many metabolic processes within the turf plant, but the most visible effects of nitrogen in turf are growth and color. Conversely, excess available nitrogen is associated with excessive unwanted top growth, increased susceptibility to fungal disease, and poor hardiness.

The natural levels of nitrogen are not sufficient to meet the growth, health and appearance expectations of many homeowners. For this reason agronomists recommend a fertilization program supplemented with nitrogen for grass plants. Nitrogen in ammonium and nitrate forms are used by the plant. Both of these forms are water-soluble and enter the plant through roots in solution with water. Fertilizers may also use urea and other forms of nitrogen that must be converted for use by the grass plant by reactions in the soil. The reactions of nitrogen in the turfgrass ecosystem can be complex and are affected by soil microbes, enzymes, soil organic matter, texture, moisture and aeration, temperature, pH and other factors.

Environmentally safe nutrient levels

The goal of fertilization is to supplement the available nutrients, specifically nitrogen, so plant health is not limited. To achieve that goal the ideal would be to provide just enough of each nutrient to achieve the desired turf quality, but no more. Excess water-soluble nitrogen can be lost through leaching or volatilization. Obviously the loss of applied nitrogen via leaching and volatilization is inefficient, costly, and can pose negative environmental impacts. One way to avoid leaching and volatilization is to provide very small amounts of nutrients on a frequent basis. An example of this is fertigation where nutrients are applied every few days in a water-soluble form through irrigation systems. This technology is not generally available to homeowners, so the alternative is to use a fertilizer with slow release nutrient (nitrogen) sources that can be applied infrequently yet feed for many weeks.

The Association of American Plant Food Control Officials (AAPFCO), defines slow release as follows:

"Slow or Controlled Release Fertilizer - A fertilizer containing a plant nutrient in a form which delays its availability for plant uptake and use after application, or which extends its availability to the plant significantly longer than a reference "rapidly available nutrient fertilizer" such as ammonium nitrate or urea, ammonium phosphate, or potassium chloride. Such delay of initial availability or extended time of continued availability may occur by a variety of mechanisms. These include controlled water solubility of the material (by semi permeable coating, occlusion, or by inherent water insolubility of polymers, natural nitrogenous organics, protein materials, or other chemical forms), by slow hydrolysis of water-soluble low molecular weight compounds, or by other unknown means. (Official 1985)."

The case for Greenview fertilizer

Most DIY homeowners apply fertilizer in a granular form. Obviously it is not practical to do this on a frequent basis due to the time and labor necessary to spread fertilizer. Therefore, there is an obvious benefit to the consumer if a product can be applied less frequently and still maintain the desired turf quality. If applications are to be made less frequently then more nitrogen must be applied with each application. If turf quality goals are to be achieved with fewer applications much of that nitrogen must be slow release to extend the period of feeding, avoid the pitfalls of excessive available nitrogen, and reduce the loss of nitrogen to leaching and volatilization. Slow release sources of nitrogen are more costly than soluble (quick release) forms. Higher slow release content is generally synonymous with higher quality and higher cost. Higher slow release content makes it less likely that nitrogen will be released before the grass plant needs it, the turf will utilize more of the applied nitrogen, and less will be lost to the environment.

Fertilizer manufacturers attempt to strike a balance between cost and slow release content (quality) to make products that are appealing to the consumer. In general, a higher amount of slow release nitrogen is better for a lawn as long as there is enough readily available nitrogen to meet the immediate needs of the plant. It’s not uncommon for golf courses and sports turf professionals to use fertilizer products that have 70% or more of slow release nitrogen for turf maintenance. Most consumer products use less slow release nitrogen because it is more expensive and the market is very cost sensitive. The Greenview strategy is to provide a fertilizer of much higher quality than those traditionally found in the cost sensitive consumer market. These Greenview fertilizer products are similar to products that have been used for many years in the professional golf and landscape markets.

How to compare a fertilizer's slow release content

By law every fertilizer must have a guaranteed analysis that describes the nutrient content. AAPFCO has set strict standards for the statement of guarantee and the type(s) of nitrogen in the fertilizer. Every manufacturer is legally accountable for providing a fertilizer guarantee on every fertilizer product and products are randomly sampled and tested to verify that those statements are accurate. The nitrogen guarantee of any fertilizer can be compared to any other fertilizer to determine how they compare on the basis of total nitrogen, ammoniacal nitrogen, urea, nitrogen, water insoluble nitrogen, and other soluble nitrogen and so on. When comparing Greenview and Scotts products, the slow release percentage can be calculated by dividing the sum of water insoluble nitrogen and other water soluble nitrogen by the total nitrogen.

Compare Greenview and Scotts slow release nitrogen content

Based on the legal labeling:

• Greenview Fairway Formula Spring Fertilizer 24-2-8 has 74% slow release nitrogen.
• Greenview Fairway Formula Fall Fertilizer 29-2-10 has 41% slow release nitrogen.
• Scotts Turf Builder with Plus 2 Weed Control has an analysis of 28-3-3 and has 31% slow release nitrogen.
• Scotts Turf Builder Lawn Fertilizer has an analysis of 29-3-4 and has 37% slow release nitrogen.
• Scotts Turf Builder With Halts Crabgrass Preventer has an analysis of 30-3-4 with 36% slow release nitrogen.
• Scotts Winterizer has an analysis of 22-3-14 and contains 34% slow release nitrogen.

See labels and guarantees for detailed information.

The following chart summarizes some of these comparisons

Sources of slow release nitrogen (methylene urea and isobutylidene diurea)

In addition to the calculation of slow release nitrogen content, each of these labels must also contain a statement of derivation that describes the components that are used to supply the plant nutrients. This “derived from” statement clearly shows that all of the Scotts products contain methylene ureas as their source of slow release nitrogen. Methylene ureas are commonly used as a source of slow release nitrogen and the primary mechanism of release is microbial breakdown. Soil microbes utilize the carbon found in the methylene urea molecule for a food/energy source and in the process release urea, which is in turn converted to plant available ammonium and nitrate. The rate of release is dependant on both moisture and temperature since these are both factors in the reproduction and metabolic rates of soil microbes.

In comparison Greenview Fairway formula contains both methylene ureas and Isobutylidene diurea (IBDU®). IBDU is recognized in the turf industry as a premium source of slow release nitrogen. The release mechanism for IBDU is a chemical reaction with water, hydrolysis, in which urea is slowly released. Hydrolysis is dependant on moisture, but not microbial populations. Therefore, this source of nitrogen works equally well over a wide range of temperatures. IBDU is particularly advantageous during peak turf growth periods in spring and fall when soil temperatures are cooler and microbial activity is still low. This dual mechanism of controlled release supply makes Greenview fertilizer more versatile under a wider range of temperature and soil conditions.

Comparison summary

The consensus of turfgrass experts is that slow release nitrogen is beneficial in fertilizer supplements, and higher percentages of slow release nitrogen correlate to higher quality of the turf. The market reinforces this where, on a cost per unit basis, slow release nitrogen sources demand higher prices than soluble forms. The labeling and characterization of nutrients on fertilizers is regulated and standardized so fertilizers can be compared based on the stated guarantee. The total analysis as well as the percentage of slow release nitrogen can be accurately derived from the guarantee and used for comparison.

Based upon a comparison of several labels of Greenview and Scotts formulas, the slow release nitrogen content of the Greenview formulas is significantly higher than those found on the Scotts products. Greenview also incorporates two forms of slow release nitrogen, both IBDU and methylene ureas. The Scotts formulas do not contain any IBDU. It is safe to conclude that the Greenview formulas are superior in their slow release nitrogen content. It is also safe to conclude that under most circumstances of application and use where slow release nitrogen offers many advantages over quick release forms, Greenview formulas will provide superior results including longer feeding, less surge growth, and less frequent application, less environmental loss, and more nitrogen utilized as intended by the turf plant.