It’s a fair question, but the answers can be complicated
It seems like one of the simplest questions that can be asked about any fertilizer product: “How long will it last?” It’s certainly a fair and, quite frankly, rather significant question. However, like the vast majority of seemingly straightforward questions in the world of golf course management, the answers are rarely ever uncomplicated.
When distributors and superintendents ask me this question, their reasons for asking are vastly different. Distributors are looking for the university research that has empirically generated a release curve for the slow-release nitrogen component, which is usually expressed in weeks or months. Superintendents are typically looking for the real-world performance they can expect from the slow-release nitrogen to feed the turf on their golf courses.
At first glance, this release curve information appears to provide the same information, but in reality it does not. Here’s why.
University research done on slow-release nitrogen longevity refers to the time it takes for all the nitrogen in the product to be released from the granule under some constant, standard root zone temperature, usually between 70 and 82 degrees Fahrenheit for most manufacturers. Comprehensive studies will repeat the same protocol with varying constant temperatures in order to provide a better overall picture of how the product performs.
Distributors and their representatives use the information from this type of research for sales and marketing purposes to help organize and categorize the different fertilizer products they offer to superintendents. It allows them to make suggestions based on superintendents’ specific golf course situational needs, which is a valuable resource.
Superintendents probe a little deeper to fully understand the performance capabilities of the fertilizer for several reasons.
One main reason is because golf courses don’t have the luxury of maintaining a constant growing medium temperature. The peaks and valleys of the temperature throughout the growing season directly affect the availability of slow-release nitrogen. In most slow-release nitrogen sources, such as SCU, PCU, PCSCU, methylene urea and methylene urea/ammonium sulfate complexes, nitrogen release is driven by temperature. When the soil temperature rises above the reference temperature in the research study, it results in quicker release and less than expected longevity. The same holds true for the reverse; colder temperatures will delay nitrogen release and extend longevity.
Another reason superintendents investigate fertilizer products is the simple fact that many golf courses don’t have the same root zone material throughout the property. With the inevitable soil profile variations, root zones with higher cation exchange capacity (CEC) and better overall soil properties will react differently than root zones with low CEC and poor soil properties. Sand root zones on putting greens have a much higher leaching rate than root zones with measurable clay content. All of these factors affect fertilizer performance.