Over the past two weeks, I've had multiple conversations about the way I think of turfgrass management. It all starts with a definition of greenkeeping as managing the growth rate of the grass. I wrote about this in A Short Grammar of Greenkeeping. You can get your copy here.
Application of the grammar allows for easy communication among turfgrass managers about the work they are doing. I'll use the creeping bentgrass greens at Hazeltine National GC as an example. Volunteers from near and far were at Hazeltine during the Ryder Cup.
Let's say that I was from Madrid, or San Francisco, or Sydney, and I wanted to get green conditions that were more like those at Hazeltine. One of the ways I would try to do that would be to apply a similar quantity of nitrogen. But how to compare locations?
I would use the temperature-based growth potential (GP). For Minneapolis, the GP looks like this.
If I set the maximum monthly N at 3 g/m2, and multiply by the GP, I get a maximum annual N of 13.3 g/m2 for that location (Minneapolis). Now I'll make up a number, because I don't know exactly what it is, but let's say the actual quantity of N applied at Hazeltine was 9 g/m2.
I'll use the log percentage (L%) difference for consistency. The L% is the natural logarithm of the ratio of two numbers, multiplied by 100:
If 9 g N were applied at Hazeltine, and the value calculated using GP as described above is 13.3 g, that is a 39 L% reduction.
If I want to apply proportionally the same amount of N at another location, I can calculate the GP amount, which I'll call a standard value, and then take a 39 L% reduction.
The standard using these calculations comes to 16.7 g at Madrid, 20.1 at San Francisco, and 28.9 at Sydney. Knowing that there was a 39 L% reduction at Hazeltine, my starting point for Madrid, after applying the same reduction, would be 11.3 g N/m2. At San Francisco, the N would go from the standard calculation of 20.1 down to 13.6 g, and at Sydney the 39 L% reduction takes N from 28.9 to 19.6.
This grammar facilitates the rapid sharing of relative inputs used to produce turf surfaces all over the world. Let's say we know there are amazing bentgrass greens in Sydney with N inputs of 10 g/m2/year. A corresponding quantity of N in Minneapolis would be 4.6 g.
This same approach can be applied for the quantity of water supplied in comparison to evapotranspiration (ET), to frequency of mowing, to evaluation of the growth rate, to assessment of the photosynthetic light, and so on. I find this approach quite useful in rapid implementation of maintenance practices that work well at location A, applied to location B. One then has a site specific starting point that can be further adjusted at location B, based on turfgrass response at that location.