The Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) requires that all pesticides sold or distributed in the United States (including imported pesticides) be registered by the U.S. Environmental Protection Agency (EPA) except where exempt from registration requirements. EPA’s registration process and associated requirements are discussed on EPA’s website.

This EPA guidance explains existing statutory and regulatory provisions regarding nitrogen stabilizers. It does not create any new requirements or exemptions from the requirements of FIFRA.

FIFRA Definition of Nitrogen Stabilizer

FIFRA Section 2(u) defines pesticides that must be registered under FIFRA to include “any nitrogen stabilizer.” FIFRA Section 2(hh) defines a nitrogen stabilizer, as follows:

"The term “nitrogen stabilizer” means any substance or mixture of substances intended for preventing or hindering the process of nitrification, denitrification, ammonia volatilization, or urease production through action upon soil bacteria. 

Such term shall not include

  1. dicyandiamide;
  2. ammonium thiosulfate; or 
  3. any substance or mixture of substances:
  • that was not registered pursuant to section 3 prior to January 1, 1992; and
  • that was in commercial agronomic use prior to January 1, 1992, with respect to which after January 1, 1992, the distributor or seller of the substance or mixture has made no specific claim of prevention or hindering of the process of nitrification, denitrification, ammonia volatilization [or] urease production regardless of the actual use or purpose for, or future use or purpose for, the substance or mixture. 

Statements made in materials required to be submitted to any state legislative or regulatory authority, or required by such authority to be included in the labeling or other literature accompanying any such substance or mixture shall not be deemed a specific claim within the meaning of this subsection.”

Discussion of Definition

Nitrogen is one of the primary nutrients for plant growth, development and reproduction; the main inorganic forms of nitrogen in soils are ammonium and nitrate. A nitrogen stabilizer is any substance or mixture of substances intended for preventing or hindering the process of nitrification, denitrification, ammonia volatilization, or urease production through action upon soil bacteria. A brief explanation of each process follows:

  • Nitrification is the part of the nitrogen cycle where soil organisms convert ammonia and ammonium to nitrite and then to nitrate-nitrogen which is available to plants. Nitrate is the form that can be moved out of the soil by leaching or lost by denitrification.
  • Denitrification is the bacterial conversion and loss of nitrate-nitrogen to nitrogen gas.
  • Ammonia volatilization refers to ammonia nitrogen loss.
  • Urease is an enzyme produced by bacteria in the soil and contributes to the conversion of urea to ammonia, which can be lost through volatilization.

Nitrification, denitrification, ammonia volatilization, and urease production denote specific undesirable actions of soil bacteria with the result that nitrogen availability is decreased.

The first item to consider in evaluating whether a product is a nitrogen stabilizer is if such a product accomplishes the purpose of nitrogen stabilization through action upon soil bacteria. The soil bacteria that convert nitrogen nutrients to nitrogen gas are considered to be pests. Substances that prevent or hinder the process of nitrification, denitrification, ammonia volatilization, or urease production through a mechanism other than action on soil bacteria are not nitrogen stabilizers.

Under 40 CFR §152.6(b)(1), living organisms are not considered to be substances. Thus a product cannot be a nitrogen stabilizer if its action depends solely on a living organism. To be subject to FIFRA, the product would also have to contain something other than a living organism that performs those functions.

EPA has identified certain phrases as claims that a product prevents or hinders the process of nitrification, denitrification, ammonia volatilization, or urease production. Under 40 C.F.R. § 152.6(b)(4), these claims include:

  • Improves crop utilization of applied nitrogen.
  • Reduces leaching of applied nitrogen or reduces groundwater nitrogen contamination.
  • Prevents nitrogen loss.
  • Prolongs availability of nitrogen.
  • Increases nitrogen uptake, availability, usage, or efficiency.

Such claims indicate that the substance has a mechanism involving action on soil bacteria. Any product that makes nitrogen stabilizer claims as listed in 40 CFR §152.6 will be presumed in the first instance to be a nitrogen stabilizer. If the producers of such products disagree, they must demonstrate that the product accomplishes its effects without affecting soil bacteria. By considering the product’s claims, composition and mode of action, EPA determines whether a product bearing such claims is a nitrogen stabilizer.

In summary, when a product that includes a substance makes nitrogen stabilizer claims, acts on soil bacteria, and is not otherwise excluded from the statutory definition of a nitrogen stabilizer or exempt under 40 CFR Part 152, then the product is a pesticide and must be registered by EPA.