Buying granular fertilizer can be a dreaded process, particularly with the recent price hikes causing many of us to rethink career choices.
There are several aspects of product usage and performance that come into play when selecting materials for this year’s program. Often, the factor that really sparks the choice is price. The question for me at that point is: what does that price really mean? I have some simple fertilizer math that may open your eyes to actual value and costs.
I know math is not what you really want to read about in terms of agronomic insights, but it is imperative in making wise business decisions. I have examples of two different 50-pound bags of product below. I will also show the math to uncover your actual cost. These calculations are based on application rates at 1 pound of nitrogen per 1,000 square feet and prices are arbitrary.
24-0-8 $30 Per Bag Calculations
- 100/24 will give you the pounds of fertilizer needed to apply 1 pound nitrogen per 1,000= 4.17 Lbs. of fertilizer required
- 50 pounds in a bag divided by the above rate (4.17) will give you the coverage per bag.
- 50/4.17 = 11,990 or 12,000 square feet of coverage per bag
- If you divide $30 by the size of the bag (50 pounds), that will give you the cost per pound of fertilizer
- 30/50 = $0.60 per pound of fertilizer
- Multiply that number by the rate and that will give you the cost per 1,000 square feet.
- 0.60 * 4.17 = Final cost of $2.50 per 1,000 square feet
16-0-8 $22 Per Bag Calculations
This sounds like a better deal already, right? Using the math above, however:
- 100/16 = 6.25 pounds/1,000 square feet
- 50/6.25 = 8,000 square feet
- 22/50 = $0.44 per pound
- $0.44 * 6.25 = Final cost of $2.75 per 1,000 square feet
Just like that, the price per bag theory of smart buying is busted! By taking just a few minutes, you can determine which is the better financial option for granular fertilizer purchases. Not only that, by using the higher nitrogen product, you reduce the application rate, requiring you to carry fewer bags to cover the same amount of square footage.
The next thing to take into consideration is the application rate of readily available nitrogen and slowly available nitrogen based on the analysis. More simply put, how much fast-release and how much slow-release nitrogen are you putting down? This question opens the discussion of why one would select a fertilizer with a slow-release component.
There are several reasons to opt for a product with at least some slow-release nitrogen, including longer-lasting feeding, less burn potential, and extended greening without pushing excess top growth.
Fast-release or readily available sources most often are in the form of urea or ammonium sulfate. These, like the name states, are essentially immediately available to the plant for uptake.
They give you quick, visual greening but also lead to more rapid top growth and can burn the plant if higher rates are applied. The other downside of quick-release sources is that they can move through the soil with some speed due to leaching or runoff, leading to product loss and water contamination.
You may be asking for some clarity regarding slow-release nitrogen. This component is sometimes referred to as SAN (slowly-available nitrogen), CRN (controlled-release nitrogen), SRN (slow-release nitrogen) or WIN (water-insoluble nitrogen).
Many fertilizers have some percentage of SRN, often in the 30% to 50% range. The Association of American Plant Food Control Officials (AAPFCO) is the governing body that regulates all of these and other aspects of fertilizer standards. It only recognizes certain materials as true slow-release sources, including:
- Synthesized products which reduce solubility
- Urea formaldehyde or Urea form
- Methylene urea
- Isobutylidene diurea (IBDU)
- Coated particles which limit contact between water and urea reducing release.
- Sulfur-coated (SCU)
- Polymer-coated (PCU)
- A combination of the above
You may have heard of products listing some of the nitrogen sources as stabilized nitrogen. These are simply granules that have had a material added to them to delay the transformation of the product applied into a usable form. The intended result is to extend the nitrogen availability of the fertilizer in the soil. To date, AAPFCO has not recognized stabilized nitrogen as a true slow-release form. If you check these labels, you will see some of those components below:
- Nitrification inhibitors—reduces bacteria that convert ammonium to eventually nitrate forms
- DCD (dicyandiamide), DMPP, Nitapryn
- UMAXX, UFLEXX, N-Serve and many others
- Urease inhibitors—block the activity of urease which converts urea to ammonium nitrogen
- NBPT (n-butyl) thiophosphoric triamide
- NPPT (n-propyl) thiophosphoric triamide
- Products like Agrotainâ and many others
I know this may be a little bit technical, but the take-home message is: don’t get fooled into thinking that stabilized sources of nitrogen are really slow-release sources. That is myth No. 2.
This is one of my favorites. I often will get the remark when recommending higher nitrogen fertilizers like 32-0-3. The question usually starts like, “isn’t that too much nitrogen?” Sure, 32% of that bag is nitrogen, but these products are labeled and intended to be applied at the rate of 1 pound of nitrogen per 1,000 square feet. That means that the application rate will be lower and the bag will cover more area.
This one surrounds the notion that there is a difference in performance between two products with close but not identical fertilizer analysis. Remember, the guaranteed analysis is the three numbers on the bag, for instance 24-5-11, which refers to the percentage of nitrogen, phosphorus, and potassium guaranteed to be in the bag, in that order. The myth is that a 32-0-4 is better than a 32-0-3, a 33-0-5, or any other example of very similar products. The reality is that these nutrients, when applied correctly, are at a rate so similar that there will be no difference.
There are exceptions to the application rate discussion above and they are especially relevant now. The biggest exception to the 1 pound per 1,000 square feet rule is when you are spreading combination products.
Combos are fertilizers that have had a pesticide applied to the particles so you can provide nutrients as well as a control product at the same time. Many granular combo products being applied right now will have a preemergent herbicide on them. It is typical to find fertilizers with Dimension, Prodiamine, and some even with Oxadiazon designed to prevent annual weeds from becoming established.
These products are perfect for efficiency in that it only takes one trip over the area to both fertilize and apply the herbicide, rather than two separate applications. These products can sometimes be a bit more pricey, but when efficiency and labor shortages enter the equation, they may make more sense.
These products also will have more rates that are dialed into applying the right amount of pesticide with the fertilizer rate being a secondary consideration. There are many other combo products formulated with post emergent herbicides as well as insecticides for ease of application and efficient operations.
Before You Start a Fertility Program
The above is really just scratching the surface of the fertilizer-buying dilemma. Here are some recommendations to follow when building a fertility program:
- Perform a soil test to better understand particular nutrient requirements.
- Always read and follow label instructions.
- Last but not least—make sure to calibrate your spreader for each product that you are using.
A greater discussion regarding enhanced efficiency fertilizers can be found here.
Need More Help with Fertilizers and Other Turf Questions? We’re Here for You
Ewing’s Tech Team, myself and Pat Gross, are here to help you with fertilizer questions and to answer any turf-care questions you have, so lean on us for expertise and product selection.