## A Fertilizer Miscellany: cost, phosphite, and nutritionism

##### 06 December 2012

Fertilizer cost

In a series of posts listed below, I've written about the most affordable nutrient sources that can be used to fertilize greens and get excellent results. The important thing is supplying the right amount of the necessary elements. The bermudagrass putting green at right was fertilized exclusively with urea and potassium chloride to supply just the right amount of N and K, and the good result is evident.

The implication is this: every turfgrass manager should be aware of what the minimum cost is, and any difference in cost between the minimum and the actual cost of fertilizer should be justified.

Then, in this post on Facebook by a fertilizer distributor, it was mentioned that “Let’s hope the financial controllers at each club don’t read it.” Actually, I think everyone involved in the management of clubs, greenkeepers, general managers, and yes, even financial controllers, should have some idea of how much the costs are. I don’t expect that any financial controllers would read this, but why greenkeepers would need to hide anything about how much money they spend on fertilizer is beyond me.

Let’s look at estimated nutrient costs in a few more cities, making the same assumptions as before: 18 holes of greens occupy one hectare, we will use the temperature-based growth potential developed by PACE Turf to estimate nitrogen requirement (shown in Figure 1 below), and we will use a maximum of 4 g N/m2/month for bermudagrass greens and 3.5 g N/m2/month for cool-season greens when growth potential is at an optimum. Let's consider estimated nitrogen requirements for bermudagrass greens at Mumbai, bentgrass greens at Madrid, and bent/Poa greens at London, England and Portland, Oregon.

Figure 1. Estimated nitrogen requirement through the year for bermudagrass greens at Mumbai and bentgrass greens in London, Madrid, and Portland, based on the temperature-based growth potential of PACE Turf.

This model predicts an annual N requirement at London, Mumbai, Madrid, and Portland of 12, 43, 19, and 18 g N/m2/year, respectively. We are using the MLSN guidelines combined with a temperature-based growth potential to estimate nutrient requirements, and for each of these soils let’s assume we have the fairly typical situation for a sand rootzone of pH at 6, P at 40 ppm, and K at 50 ppm. In this case, we will apply N based on the estimates shown in Figure 1, no P is required, and we will apply K at half the N rate to meet the full grass requirement. Using urea and potassium sulfate to supply these nutrients, how much does it cost?

Figure 2 shows the accumulated fertilizer cost for each city through the year, using local fertilizer prices from the fourth quarter of 2012 at current exchange rates, with all prices expressed in USD for convenience.

Figure 2. A step chart showing the cost for nitrogen and potassium to fertilize 18 greens for one year with urea as the N source and potassium sulfate as the K source.

Portland is the most expensive, with an annual cost of about $700. Mumbai, although it is the location using the most fertilizer, has the cheapest cost, at less than$500 per year, because of government subsidies for these fertilizers. These prices are similar to those estimated previously for Thailand, Vietnam, Japan, and Canada.

These are the baseline costs, then one can spend more, but one should be able to justify the added expense in fertilizer by whatever improvement one can get over the results one gets with urea and potassium sulfate.

Phosphite is not a fertilizer

I'm sometimes asked if phosphite is a fertilizer or a source of P to grass. Some people claim that phosphite is a nutrient. In plain terms, we can say that phosphite is not a fertilizer.

Phosphite does not provide plant P nutrition and thus cannot complement or substitute phosphate at any rate.

Phosphite does not have any beneficial effect on the growth of healthy plants.

Indirectly providing P by phosphite to phosphate oxidation is not an effective means of supplying P to plants compared with phosphate fertilizer.

These quotes are all from Soil Science and Plant Nutrition in an article by Thao and Yamakawa entitled Phosphite (phosphorous acid): Fungicide, fertilizer, or bio-stimulator

To prevent pythium, yes, phosphite is an effective fungicide. But as a fertilizer? It is not effective at all. And as a broad spectrum fungicide? It's not that either.

Nutritionism

John Foy, director of the USGA Green Section’s Florida Region, recently wrote an article about nutritionism. When such a knowledgable and well-respected figure writes about this topic, we have a great chance to learn from his sage advice.

For me, there are three key points in the article. First, Foy explains nutritionism and then cautions against “focusing on individual nutrients far and beyond what is practical or necessary.”

Second, he discusses products that go beyond supplying the basic macro- and micronutrients and that are reported to enhance turf health, noting “there is still not enough unbiased research to support most of the claims being made. Also, there are questions about whether or not the increased costs are justified.”

Third, he concludes by stating that a reliance on nutritionism “is not the answer or even a proven approach in sustainable turfgrass and golf course management.”

This is excellent advice. The fact is, turfgrasses are deliberately and rightly maintained to be deficient in nitrogen. If all the nitrogen the grass could use was applied, the grass would grow much too fast. For this reason, it is almost unheard of to have a deficiency of any other element, and that is why the MLSN guidelines are so effective, why applying the right amount of nitrogen is so important in producing good turfgrass conditions, and why we can create such fine turfgrass surfaces, as pictured here, by using the very basic nutrient sources.