Fertilizers: the stories keep growing

Anecdotes about fertilizers sometimes acquire a life of their own. They can achieve mythic proportions as stories are passed on that relate astonishing rates of growth, blooms that never seem to quit, or perhaps more tomatoes than you ever thought possible to get from one plant. The one I've always found the most amusing is the myth of the urea-based product that would eat through hard pan, thereby improving drainage as well as providing nitrogen to the plant. (This was explained to me with utmost seriousness by someone who had used the product when he planted a tree. How he determined that the hard pan beneath the tree had disappeared is not clear to me.)

Like many myths, anecdotes of miraculous fertilizers often stem from ignorance. This was all too apparent when I worked for a retail nursery. The typical customer's level of knowledge approached zero. Most had little more than a vague notion that nitrogen was important to plants in some way or another. Fortunately, most turf and landscape managers possess enough knowledge to shield them from ridiculous claims, which often are initiated by unscrupulous marketers.

As is often the case, research presents us with a relatively mundane picture of plant fertility. A fair number of studies suggests that many reports of dramatic responses from fertilizer applications simply point to a pre-existing deficiency. Applying additional nutrients when adequate levels already are present often yields little or no benefit. More is not necessarily better. It can even be harmful.

Additionally, despite the many available fertilizer products for turf and ornamentals, plants actually are able to use primarily just two forms of nitrogen: nitrate and ammonium. It would be erroneous to believe that the nitrogen in a particular product, once taken up by a plant, provides some unique advantage relative to other nitrogen fertilizers.

Am I suggesting there's no difference between fertilizer products? Of course not. Tremendous differences exist. But it might be more useful to focus on the "how" rather than the "what." How does the product release its nitrogen? How consistent is the release pattern? How is it formulated, and how does that formulation fit your needs? Does the plant actually need what you're giving it?

These are crucial questions that we address in this issue, which focuses on fertilization. Dr. Elizabeth Guertal, an Auburn University soil-fertility specialist, gives us a look at nitrogen sources and their pluses and minuses in "Nitrogen: finding the form that fits" (page 14).

Finding the right fertilizer is important, but applying it accurately is just as critical. And for that, you need a spreader and the knowledge to use it properly. Find out about both in this month's "Equipment Options" on large-area broadcast spreaders (page 40).

Contrasted to turf fertility, tree fertility has remained an enigmatic subject. South Dakota State's Dr. John Ball discusses how the new ANSI 300 fertility guidelines address this topic in Prescription fertilization: ] for trees (page 32).

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