By Daniel Hudson, UVM Agronomist
Some timely, serious, and even controversial questions have recently been raised about the efficacy and safety of various “fertilizer enhancers.” Urease inhibitors are one such product, and they are a relevant subject for those who are planning on applying sidedress nitrogen to corn fields in the next few days. The purpose here is not to promote a particular brand of urease inhibitor, but to strongly discourage farmers from expending resources on products that are not effective. As it turns out, only two products are mentioned in this discussion.
A quick review for context:
‘Urease’ is an enzyme that is present in microbes, plants, and throughout the soil. As the name suggests, urease functions to break down urea; the byproducts of the reaction are ammonia and carbon dioxide. If urea or UAN (a mixture of urea and ammonium nitrate) fertilizer is applied to the soil surface and not quickly followed by enough rain to move it into the soil, MUCH of it can be lost by volatilization through the activity of urease. Heat, soil moisture, and wind all promote volatilization.
If the urease molecules local to the droplet or granule of fertilizer are inhibited, these volatilization losses can be reduced. At least one product that claims to be a urease inhibitor has been proven to work; at least one has been shown not to work as claimed. A product that does not work costs you more than just the cost of the product – the urea portion of the fertilizer is still unprotected and vulnerable to volatilization losses.
What the research says…
Getting to the point, I will focus on only two products for which urease inhibiting claims are made. Other products may exist. The trade names of these products are NutriSphere-N® and Agrotain Ultra®. While this is certainly not an exhaustive review of the subject, the studies mentioned are representative of the conversation in the literature from independent researchers.
Research done at Cornell concludes that the active ingredient of Agrotain® (NBPT) does effectively function as a urease inhibitor while the active ingredient of NutriSphere-N® does not. After studying in the laboratory and in wheat and rice systems, researchers from ND, MS, and AR concluded that NutriSphere-N® “. . . has no urea volatilization inhibiting properties at recommended rates . . .” The one source of consistent positive yield results (of which I am aware) from NutriSphere-N® comes from a former faculty member from Kansas State University. On pages 5 and 6 of a document called Nitrogen Extenders and Additives for Field Crops, those findings are described as ‘curious’ in light of the body of contradictory evidence.
Finally, a concern has been raised about the possibility that one of the ingredients of an Agrotain® product could pass through cows and into the milk supply. This concern is based on a situation in New Zealand where an ingredient from one Agrotain® product (Agrotain Plus®) was found in dried milk products. The ingredient of concern, a nitrification inhibitor abbreviated ‘DCD’, is found in Agrotain Plus® but not in other Agrotain® products such as Agrotain Ultra® or ADII® (‘Agrotain® Dry’). Again Agrotain Ultra® and ADII® contain the appropriate urease inhibitors to use with sidedress nitrogen on corn in the Northeast; they do not contain DCD and have not been found to pass through to the milk.
Disclaimer: the purpose of this article is not for UVM or myself to promote the Agrotain® brand. The active ingredient found in Agrotain® (known as NBPT) is the only commercially available product in the U.S. that has been shown to actually function as a urease inhibitor. As far as I know, there are no other brands of fertilizer enhancers that have NBPT as an ingredient.
Agrotain® labels: http://www.agrotain.com/agrotaininfocenter/labels/
NutriSphere-N® label: http://sfp.com/product-labels/Nutrisphere-N-for-Liquid-Nitrogen-Fertilizer-Label.pdf