This fertilizer schedule seems strange to me now

A lot of turfgrass nutrition research gets done with fixed rates of fertilizer applied on a fixed time schedule. It always seemed normal for me to fertilize this way.

Here are a few examples.

From some of my PhD research, 20+ years ago: “Potassium fertilizer was applied to the plots as K2SO4 at 6 rates (0, 1, 2, 3, 5, and 6 g K m-2) at 14 day intervals”

From a recently published article by other researchers: “In all locations, putting green plots received urea (46-0-0) on a 14-day interval at a rate of 5 kg ha-1

From another recently published article by other researchers: “K (potassium sulfate) applied at 0, 3.4, 6.9, and 13.8 kg ha-1 every 2 weeks and N (urea) applied at 4.9 kg ha-1 every 7 or 28 days”

Lots of research gets done with fixed rates and fixed application schedules. Then the results of these research projects get taught to students, or communicated through continuing education to industry professionals, as something like “the best-performing treatment was rate X applied every 14 days.”

But the grass demand for nutrients like N and K is not only related to those fixed application rates. How much the grass is actually growing, and the weather the grass is experiencing through the year, that has something to do with the nutrient demand too. Have a look at these charts, for example.

Then there’s the chart above with sand topdressing prediction based on temperature variation, and consequently changes in expected growth, through the year.

If we were looking at flat lines on these charts, that’s what would match to a fixed fertilizer schedule. But the lines aren’t flat. The implication of this is that fertilizer trials to turfgrass supplying a fixed rate on a fixed schedule are applying rates that vary in response to the plants demand for nutrients at the time. Sometimes the rate might be too low, and sometimes the rate might be just right. Or too high. Or way too low. Or all of the above, depending on the time of year.

Turfgrass managers who adjust nutrient supply based on GvX are able to apply, from the plants’ perspective, a much more stable rate of nutrients. I understand the practical difficulties in adjusting rates in research. But there are also practical and logical difficulties in not adjusting rates. I’d like to see more research done in the future with nutrient supply adjusted based on GP or based on how much the grass is growing.

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