Turf[TECH]Report - Controlled/Slow Release Fertilizers  [Part 2]

April 17, 2018

Understanding CRN/SRN Release Label Language and Product Review

This segment of Turf[TECH]Report, is the second of a two-part series. Part 1 focused on how controlled/slow release fertilizers work, and how to compare the various technologies. This series, Part 2 takes the time to teach you how to read and understand controlled/slow release label language and review the different kinds of products on the market. This article will supply you with all the important information you need to determine which slow/controlled release fertilizer is best for you.

How to Read and Understand a Slow Release Nitrogen Fertilizer Label 
Every label containing SRN will show the total amount of nitrogen, the form(s) and percentage(s) of nitrogen, the raw ingredient(s) nitrogen is derived from, and the percent of slow release nitrogen in the bag (as well as the source of the SRN). Let’s break down what these numbers mean. 

This fertilizer mix contains 8% nitrogen in the bag and contains Polymer Coated Sulfur Coated Urea.  7.2% of the total bag is urea nitrogen. This means that 90% of all the nitrogen in the bag is slow release urea nitrogen (7.2%/8.0% = 90%). This does NOT mean that 90% of the bag is slow release nitrogen, only that 90% of the total nitrogen is slow release. The remaining nitrogen (.8% of the total bag by content) is ammoniacal nitrogen. Understand that the asterisk at the bottom says *7.2% slowly available nitrogen from polymer coated urea. Because this 7.2% value is the same as the 7.2% urea nitrogen value at the top, we can infer that 100% of all the urea in this fertilizer is in the form of slow release.  In other words, there is no “straight urea” floating around in this mix. 100% of the urea is coated. Remember, all percentage values on labels are always based on the total amount of that specific ingredient in the entire bag, NOT the percentage of an ingredient within an elemental subsection. 

This fertilizer mix contains 20% total nitrogen in the bag. 10% of the entire bag is ammoniacal nitrogen.  Only 1% of the bag is straight urea nitrogen. 4.8% of the bag is water insoluble nitrogen (WIN) (from MU). This means that 4.8% of the nitrogen is not readily accessible and cannot be used by plants until is converted into a usable form (such as straight urea). It takes time for WIN to become accessible (hence WIN is a form of slow-release). Also note that 4.2% of the bag is water soluble nitrogen (WSN) (also from MU). This means that while this nitrogen is still not ready for use by plants, 4.2% of nitrogen is readily dissolvable in water and is ready to be acted on by the environment (in this case, microbes) for conversion into straight urea, which can then be converted once more into usable nitrogen for plants. In the case of this example, the WIN and WSN add up to 9%. The statement at the bottom indicates that 9% of the entire content of the bag is slow release nitrogen (sometime called “slowly available nitrogen”) and is derived from methylene urea. (Remember, the release of MU nitrogen is based on the activity of soil microbes). If the total amount of nitrogen in the bag is 20%, and 9% is slow release nitrogen, then 11% must be the total amount of immediate release nitrogen in the bag.   

Brining It All Together – Reviewing the Benefits of SRNs 
The math and science behind how the guaranteed analysis of an SRN label is calculated can become confusing, especially when terms such as “controlled release,” “slow release,” “water soluble nitrogen,” and “water insoluble nitrogen” are often used interchangeably and/or misapplied. Regardless of what something is called, all that matters is understanding the mode-of-action behind the type of slow release nitrogen inside your bag of fertilizer. It is also important to remember that some fertilizers contain 100% SRN, while others contain a mix of both slow and immediate release nitrogen. If you are unsure as to exactly what you are purchasing, always ask the manufacturer or retailer questions so that you don’t end up purchasing the wrong product for your situation. 

Summary of Slow Release Nitrogen Specs and Benefits: 

  • SRN comes in two forms: coated and reacted 
  • Coated: encapsulated urea granule; coated with sulfur, polymer, wax, or any combination thereof 
  • Reacted: chemically or biologically converted by microbes; this slow release is highly influenced by temperature and moisture 
  • Each SRN has a different release profile based on the chemistry and physical science of the fertilizer granule 
  • Release curves report the nitrogen release profile of a SRN and can be used to compare different products 
  • SRNs help deter leaching and volatilization 
  • SRNs are safer for plants; they shift the pH of the ground significantly less than IRNs (burning plants is virtually impossible, even if accidently overapplying fertilizer) 
  • SRNs help reduce the number of fertilizer applications in a growing season resulting in significant labor and energy cost savings.
  • SRNs are biodegradable and environmentally friendly 

What Slow/Controlled Release Nitrogen products does Turf Care offer? 
TurfCare™ Supply offers a wide variety of premium SRNs with a well-established reputation for quality and reliability in the turf and ornamental industry. All of our products are available in standard size granules, with some offerings in mini (smaller) and elite (smallest) sizes. 

Featured Products:   

  • SCU 
  • PCU (featuring Duration CR® with 45, 90, 120, and 180-day release times) 
  • PSCSU (featuring XCU®) 
  • MU (featuring Nutraline®) 

To view TurfCare's Slow Release Nitrogen options on different fertilizer analyses download our Product Catalog for details.  
CLICK HERE for more information on locating your local distributor to order.   

For further questions about controlled/slow release nitrogen technology, email info@turfcaresupply.com or call TurfCare™ Supply  at (877) 220-1014. For technical questions, contact TurfCare’s Agronomist, Joe Marchinchin at jmarchinchin@tcscusa.com 







Publication:  Controlled Release Fertilizers – AgIndustries Research & Consulting 

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