The purpose of this article is to provide an overview of three often-asked questions related to slow-release nitrogen: (1) what are slow-release fertilizers, (2) why should I use slow-release fertilizers and (3) when should I use slow-release fertilizers? It is important to note that products mentioned in this paper do not reflect an endorsement of the product, but simply to inform which products are currently available for crop production in WI. Likewise, a lack of mention of specific products does not imply that a product is not recommended or available for use.

What Are Slow-Release Fertilizers?

Slow-release is an often overused term that encompasses several N fertilizer products which include: uncoated slow-release fertilizers (SRF), coated SRF, and bio-inhibitors. The term “controlled-release” is often used synonymously with slow-release, but has also been used to identify coated SRF or more specifically, polymer-coated urea (PCU, often referred to as poly-coated) products. Thus, a more appropriate nomenclature that encompasses all of these products is fertilizer technologies. The debate will continue for some time regarding how much “control” each technology has on releasing N to the plant.