3/28/2023 - By Dr. Jeff Atkinson

Fertilizer labeling can be inconsistent from manufacturer to manufacturer. Harrell’s sticks to state regulations and guidance as described by the Association of American Plant Food Control Officials. To ensure a fertilizer blend matches an agronomic objective, a few important pieces of information should be considered on each fertilizer label before application.

When purchasing a pesticide, it is immediately clear what is included in the bag or jug. Percent active ingredient, formulation type, and manufacturer are easily determined by referencing information required by the Environmental Protection Agency (EPA) to be included on every pesticide label. Unfortunately, fertilizer labels often do not provide the same level of clarity.

Understanding the Fertilizer Label

While pesticides are regulated on both a federal and state level, to date, fertilizer regulations are left to just the states. Without guidance from the federal government, inconsistency in labeling between manufacturers is common. The Association of American Plant Food Control Officials (AAPFCO) is an organization made up of members from state regulatory agencies, with the objective to develop uniformity among state fertilizer regulatory agencies. The definitions and label recommendations formulated by AAPFCO bring clarity and consistency to fertilizer labels, providing enhanced protection and information for the consumer. A fertilizer label that follows AAPFCO guidelines is rich in information of agronomic importance.

Here are 7 pieces of information to consider on a fertilizer label before application:

#1 N-P-K Analysis | Understanding a Fertilizer Label

Every fertilizer, regardless of ingredients, will include three numbers separated by a dash and often placed in a prominent location. In the example below these numbers are 24-8-12 and indicate the blend includes 24% nitrogen, 8% P2O5, and 12% K2O.

For example, a 50 lb bag would contain 12 lbs of N, 4 lbs of P₂O_5, and 6 lbs of K₂O. If the desired nitrogen application rate is 1 lb nitrogen per 1000 square feet, this bag will cover 12,000 sq. ft. It’s important to note that P₂O₅ and K₂O percent are different than elemental P and K. To calculate elemental P and K, the P₂O₅ and K₂O percent must be multiplied by 66% and 83%, respectively.

Figure 1. N-P-K analysis is a key component of every fertilizer label.

#2 Guaranteed Analysis | Understanding a Fertilizer Label

While the N-P-K analysis describes the total percent of nitrogen, phosphorus, and potassium in a blend, the ‘Guaranteed Analysis’ includes this information in greater detail, along with the percent of other macro and micronutrients included in the blend (Figure 2). Information such as the percent of soluble and insoluble nutrients (aka immediate plant available vs. unavailable) and form(s) of nitrogen is also described here.

Figure 2. The Guaranteed Analysis provides more detail about the forms of nitrogen and the percent of other macro and micronutrients in the blend.

#3 Derived from Statement | Understanding a Fertilizer Label

Using the example above, a variety of ingredients can be included to formulate a 24-8-12 fertilizer blend. If only looking at the N-P-K analysis or Guaranteed Analysis, an applicator may not be able to determine how long the fertilizer will feed, its burn potential, or if the ingredients are appropriate for the agronomic situation. This information can be found in the ‘Derived From’ statement. The ‘Derived From’ statement is typically located directly below the fertilizer guaranteed analysis and includes the recipe list of the fertilizer blend.

For example, a ‘Derived From’ statement for two unique 24-8-12 blends are included in Figure 3 and Figure 4. The blend in Figure 3 is comprised of nitrogen and potassium ingredients which each have a high salt index or increased likelihood of causing fertilizer burn. Alternatively, the blend in Figure 4 is comprised of POLYON® fertilizer coated nitrogen and potassium ingredients, which have an extremely low salt index and low likelihood of causing fertilizer burn.

Note - This information is not accessible by only looking at the N-P-K or guaranteed analysis.

Figure 3. This 24-8-12 blend has a high salt index and a high potential to cause fertilizer burn.

Figure 4. this 24-8-12 blend has a low salt index and very low potential to cause fertilizer burn.

#4 Bulk Density | Understanding a Fertilizer Label

The efficacy of a granular fertilizer blend is limited by the calibration of the spreader that applies it, regardless of the quality of the ingredients. The bulk density of a fertilizer blend, or pounds of fertilizer per cubic foot, is an important piece of information when beginning the calibration process. Unfortunately, bulk density is not listed on all fertilizer labels; however, bulk density can be found below the Guaranteed Analysis on all of Harrell’s fertilizer labels (Figure 5).

Along with application rate, particle size, and spreader type, bulk density can be entered into Harrell’s Spreader Calculator to determine the spreader setting start point for spreader calibration. Due to manufacturing variation, wear, and tear, walking speed, etc., every spreader is different, so the setting suggested by Harrell’s Spreader Calculator should be confirmed for accuracy before full-scale application.

Figure 5. Bulk Density is included on all Harrell's fertilizer labels and is an important piece of information for accurate spreader calibration.

#5 Active Ingredient(s) | Understanding a Fertilizer Label

In today’s tight labor market, everyone is looking for ways to be operationally efficient. Sparging pesticides on a fertilizer carrier is a great way to accomplish two tasks at once. The process allows for the application of fertilizer and a pesticide, such as a preemergence herbicide, in a single application. If a fertilizer blend is sparged with a pesticide, it should be described on the fertilizer label as illustrated in Figure 6. Some blends may include more than one active ingredient.

Figure 6. If a fertilizer blend is sparged with a pesticide, the sparge ingredients and concentration should be described on the fertilizer label.

#6 Controlled-Release Statement | Understanding a Fertilizer Label

If a fertilizer blend contains controlled-release fertilizer, the label should describe how much of the nitrogen included in the blend is controlled-release. Buyer beware, there is no minimum amount of controlled-release fertilizer required to claim ‘Controlled-Release’ in fertilizer marketing materials. All Harrell’s blends that include a controlled-release POLYON fertilizer include a controlled-release statement below the Guaranteed Analysis, which describes exactly how much controlled-release fertilizer is included in the blend. In Figure 7, the blend contains 20.87 units of controlled-release nitrogen, or 87% of all nitrogen in the blend.

Figure 7. All Harrell's POLYON blends include a controlled-release statement that describes the amount of controlled-release fertilizer in the blend.

#7 Manufacturer | Understanding a Fertilizer Label

Harrell’s takes pride in the selection, processing, and blending of raw materials. The cumulative effect of these efforts is high-quality blends and guaranteed performance for POLYON fertilizer blends. Reach out to your local Harrell’s rep for more information, or to understand how a fertilizer blend matches up with specific agronomic objectives.