Have you ever really thought about what is actually in the bag of fertilizer that you are using?

Given, there are 50 pounds of something in every 50 pound bag and most golf course superintendents just assume it is fertilizer. Well I hate to be the bearer of bad news, but that is not always the case. 

Unfortunately, the regulatory agency that is responsible for fertilizers is a group called the American Association of Plant Food Control Officials (AAPFCO) and they do not require fertilizer formulators to put on the fertilizer labels everything that is present in the bag. They require them to put the nutrients that are in the bag, but they do not require any specifics about any “inert” ingredients.

In recent years, as we all know, the economy has not been just “kicking” so industries such as the golf business have fallen victim to this recession. Golf maintenance budgets have been reduced and fertilizer formulators have tried to figure out ways to lower the price points for their fertilizers.

One way of lowering the cost of a fertilizer is to simply take some fertilizer out of the bag and replace it with “filler”. Filler can be anything from corn cob, clay, limestone, etc….. These fillers are not fertilizers but merely occupy space and provide weight.

One of the most expensive components in a bag of fertilizer are the slow release materials. Many of the fertilizer formulators have started promoting and selling these “diluted” blends of fertilizers with more filler as a way of lowering the cost of the fertilizer. This was in reaction to the fact that many golf course superintendents still make fertilizer purchase decisions based on the cost per bag or cost per ton of the fertilizer without taking into account things like what is in the bag, how much slow release, how long the fertilizer will last, etc.

Yes, these “diluted” blends do have a lower price point per bag or per ton, but agronomically you are getting short changed. 

So, how can you determine how much filler is in the fertilizer you are considering? The easiest way is to ask the fertilizer sales person for a print out of the formulation sheet that contains the formula or recipe for making this product. If you add up the fertilizer components and then subtract that from 2,000 pounds, then you will know how many pounds of filler is in the blend or more than likely the formulation sheet will have how many pounds of filler that this particular blend calls for. The only other way is to actually do the formulation on paper yourself which would require knowing the fertilizer components used which is required by AAPFCO to put on the fertilizer label. Then, take these components and using their percent of nutrient they contain to make these calculations. I would ask the sales representative!! If they can’t provide that or do the math for you, then you need a new sales representative.

What would be considered a “diluted” blend? This is a difficult question with many answers. One such opinion may be a fertilizer that contains too much filler. Another answer could be a fertilizer that contains any filler. In my professional opinion, I look more at the amount of slow release components that are in the blend. Since these slow release components are the most expensive components, then superintendents should be sensitive to how much of these are present. More importantly, if there are sufficient amounts of these slow release components present so the slow release can work as designed to provide a consistent turf response over the allocated release time.

From an agronomic point of view, it is easy to tell you what the end results will be from the use and application of these “diluted” blends. Aesthetically when these “diluted” blends are applied the turfgrass will develop this “mottled” appearance where you see spots of different colors of green to yellow turfgrass. The turfgrass remains green where the slow release components are located and releasing while the other turfgrass areas become chlorotic due to the lack of fertility. The filler in these products will produce no turfgrass response. The water soluble or fast release components in the fertilizer will release within a few days of application and provide a turfgrass response for a week or two. Then, the only thing left in the turfgrass to provide a response is the slow release component(s).

If the fertilizer only contains 25% slow release, then you can see that it would be impossible to have the slow release components evenly distributed over the treated area.

My threshold in terms of how much slow release should be utilized in a blend is 70% slow release or more. Anything less than 70% will be a challenge to have sufficient particle distribution that is evenly distributed when applied over the treated turfgrass area to get an even turfgrass response. Why waste money on a “diluted” blend that will not perform any better than a 100% fast release fertilizer? If you are applying a slow release fertilizer to get a slow release of nutrients, then you need to make sure you have sufficient amount(s) of the slow release in the bag to allow these particles to be evenly distributed on the turfgrass when it is applied so the turfgrass response remains consistent over the length of the slow release period. This becomes more of a problem with the larger the particle size of the fertilizer blend due to fewer particles per pound.

Below is an example of a “diluted” fertilizer blend and how much filler is in the blend along with the issues of spread rate of such a product.

24-0-11 with 50% XCU Label

This is the recommended information that AAPFCO requires to be on a fertilizer label. The fertilizer components are given in the “Derived from:” statement which will list all fertilizer components used to make this fertilizer blend. The label also shows you how much slow release component(s) are in the bag with the * footnote “12.0% slow release NITROGEN derived from Polymer Coated Sulfur Coated Urea”. This is the XCU slow release component in this fertilizer blend. If you do the math, the total N content is 24% so if 12% of the N content is from XCU, then that equals a 50% blend.

If you look at the formulation sheet or do the math, you will see that to get a 50% blend with XCU for this product would require 558 pounds of XCU per ton. And, if you do the rest of the math you will find that this fertilizer blend also contains 405 pounds of filler, which is almost as much in terms of pounds as the slow release component itself.

If this product were to be applied at a one pound of nitrogen per 1,000 square feet rate, then the spread rate would be 181 pounds of product per Acre. When you look at the XCU component in this blend, at this spread rate then you are looking at trying to evenly spread 50 pounds of XCU per Acre with this application. That would be impossible to do, so this is what causes the turfgrass “mottling” appearance. This would not be a fertilizer that I would either use or sell to a golf course superintendent even if they ask for it. So what are you buying – fertilizer or filler?