Have you ever looked at a fertilizer label and wondered what it all really means? Or why it’s formatted the way it’s formatted?
Fertilizer labels and their respective guaranteed analyses can often seem confusing, but there are rhyme and reason to them. While each state has its own fertilizer regulatory program and fertilizer label requirements, the Association of American Plant Food Control Officials (AAPFCO) “strives to gain uniformity among each of these entities without compromising the needs of the consumers, protection of the environment, or fair competition among the industry.” So, while states don’t technically have to follow the AAPFCO guidelines, most states do. Each year AAPFCO publishes an updated Laws and Regulations Handbook that includes (among other things) official terms and definitions for fertilizer programs broken down by each element (N, P, K, etc.) along with approved beneficial substances that could be included on labels.
Nitrogen in Fertilizer
Nitrogen is an interesting element on a label as the form of nitrogen matters when it comes to its use in the plant and overall availability. As of 2017, there were 57 different nitrogen-based products in the AAPFCO handbook. These products ranged from “acidulated fish tankage” to “wheat middlings” and everything in between. Obviously, if you’re running a program and trying to calculate the lbs. of N per thousand you’re applying, it’s nice to know if the N is available, when it’s available, and how the plant will treat that particular form of N. Hopefully this article will help clear things up a little!
When looking at a fertilizer label, there should always be a section called “Guaranteed Analysis.” This section will show the amount of each nutrient as a percent by weight. For nitrogen, it will show a breakdown of the specific type of nitrogen content.
The Solubility of Nitrogen Content
From an applicator’s standpoint, it’s perhaps most important to note the solubility of the nitrogen content first. If it’s insoluble, it will say “x.x% Water Insoluble Nitrogen” under the total nitrogen content (listed as Total Nitrogen (N)……………………..x.x%). If the nitrogen is insoluble, it will take some time for the nitrogen to become soluble (therefore available). If you’re applying every week, every other week, etc., it’s going to be important to take this in account. Water insoluble nitrogen sources are often organic (carbon-containing) nitrogen sources that are usually larger in molecular weight. It takes time for the biology in the soil, and the organic acids exuded from the plants at the rhizosphere to work on these molecules, and make them water soluble, and plant available.
Amount of Slowly Available Nitrogen
The second item to note in regard to nitrogen would be the amount of slowly available nitrogen. If there’s slowly available nitrogen, there will be a breakdown under the total nitrogen that states, “x.x% Slowly Available Water Soluble Nitrogen*.” The asterisk will show up again under the derived-from list of ingredients and will state the source of the slowly available nitrogen.
Two of the most common sources you’ll see listed there will be methylene urea(s) and urea triazone. These are produced from the reaction of urea and formaldehyde. While they are recognized as being slow-release nitrogen sources, I think it’s important to point out that these types of products are applied in agriculture via foliar application at spray rates of 10 gallons per acre at times out of airplanes. When one considers the canopy density of the crops on which the applications are made (corn and soybeans for example), it’s doubtful that much of the product ever reaches the soil. In many cases, these compounds can be relatively low in molecular weight, and as such, should be foliarly available. In the world of turf, when using these products with these compounds, it’s a safe bet to assume that a good portion of the material is being taken up foliarly. The portion that isn’t will be worked on by biology over time and will become available for uptake via the roots after some time.
Percentages of Ammoniacal, Nitrate, and Urea
Once you’ve sorted out whether the total nitrogen is comprised of soluble or insoluble nitrogen sources and the percentage of each, the next job is to study the ammoniacal, nitrate, and urea percentages. These should all be listed out separately under the total nitrogen as “x.x% Ammoniacal Nitrogen,” “x.x% Nitrate Nitrogen,” and “x.x.% Urea Nitrogen” in that order and format. Ammoniacal and nitrate nitrogen are available for immediate uptake into the plant through the roots. Urea, depending on the type of plant, is either immediately available or isn’t.
Plants that grow in areas where the soil is often wet and lower in oxygen (and therefore lower in nitrogen-fixing bacteria) can take up nitrogen in the form of urea (river birches and pecan trees are both excellent examples). On the other hand, turf does not. As such, the urea must be converted into ammonium before it can be available through the roots. All of these nitrogen sources can theoretically be taken up through the foliage, with perhaps urea (as a neutrally-charged molecule), and nitrate (as a negatively-charged molecule) having better foliar uptake than ammonium.
Other Water Soluble Nitrogen
You may see another category of nitrogen listed under total nitrogen as “Other Water Soluble Nitrogen.” This where things get interesting! Up until this point in time, we’ve operated under the assumption that the nitrogen listed on the label will either be taken up as urea, modified urea, ammonium, or nitrate through the foliage or through the roots. The category of other water soluble nitrogen is a catch-all for all other forms of nitrogen that may be in the mix. This could be a plethora of molecules because there are 57 different types of nitrogen-based products that are approved to be listed on a label.
On many Foliar-Pak labels, you’ll likely see protein hydrolysate, and more specifically, soy protein hydrolysate. AAPFCO lists the definition of protein hydrolysate as “The organic material obtained by the hydrolysis of proteins to their constituent amino acids and short polypeptides. They are a source of nitrogen. The definition is used by prefixing the term with the name of the protein from which the hydrolysate is derived. Examples include Fish Protein Hydrolysate or Soy Protein Hydrolysate.”
While AAPFCO lists amino acids as a nitrogen source (and others may agree), it is the belief of the team here at Foliar-Pak that when taken up as an amino acid, they’re used differently than just a raw form of nitrogen in the form of ammonium, nitrate, or urea. Research has readily shown the ability of an amino acid to be taken up through the roots and through the foliage (stay tuned for Foliar-Pak’s own proprietary research on this subject in the future). If one recognizes this, then it’s important to recognize that as a downstream nitrogen source, these amino acids are going to provide a different effect from a plant metabolomics perspective than ammonium, nitrate, or urea in the plant. As such, I believe that when it comes to this category of “Other Water Soluble Nitrogen” that applicators must hold this category separate from their total nitrogen goals. It’s likely that amino acids will make one’s program more efficient and that historically acceptable levels of nitrogen in a program can likely be reduced to account for the increased efficiency of the plant’s metabolic processes. That’s a different subject for another day though.
What is important to understand today is that not all nitrogen sources are treated equally by the plant and not all of them are available at the same time or in the same way. As such, when looking at a label and calculating the respective N that the particular product supplies, I hope that this article provides you with a better understanding of what is and is not in the product from a nitrogen perspective. Understanding this can make the difference between running the appropriate amount of total nitrogen for the job or not. While it’s simple to just look at the total nitrogen content on a label and plug it into a program on Excel, plant physiology, soil ecology, and plant metabolomics demand that we take a closer look and that we understand the nuances of different nitrogen forms in a product.