Chapter 13 “I don’t really need any data for this to be certain”
Paul Robertson started a conversation22 on Twitter in 2017 that eventually touched on the quantity of clippings mown from the turf, how much the grass is growing, and the green speed. I was reminded of a question from a correspondent a few months ago. He wrote with this question:
“Have you correlated yield to speed? I have to assume that as yield changes speed changes also.”
"In the big picture view, yes the clipping volume will be negatively correlated with speed. When clipping volume goes up, the speed has to go down.
I don’t really need to show any data for this to be certain. Take, for example, warm-season greens. Are they faster when growing in August (clipping volume is a positive number), or when dormant in February (clipping volume is 0)? They are lightning in February and of whatever speed they are in August.
I attach a chart with clipping volume in L/100 m2 (same as quarts per 1000 ft2) on the x axis and green speed on the y axis. That’s from a couple years of tournament week measurements in Japan. Speed is affected by other things but the clipping volume is sure to have some effect and I don’t think it will ever be in the direction of more growth = faster speeds.
This is the chart I attached.
Today I looked up the data from 2016 and added it to the chart, and this includes a couple measurements from July 2016 a month before the tournament week.
Here it is without the July measurements.
And here are the data broken down by year.
Bill Kreuser showed data on bentgrass where the quantity of clippings was not related to the previous day’s stimpmeter measurement. Those data (https://twitter.com/UNLturf/status/879015787524104194) are surely correct. But if one thinks about the big picture view, of the range of growth rates one can have over the course of the year, and the range of green speeds, I think it makes sense to think of green speed as being affected by how much the grass is growing.
And this leads me to something else that I can’t help but mention. Bill can show data that demonstrate an interesting point; clipping yield was unrelated to green speed under the conditions of his experiment. I can show data that demonstrate an interesting point; clipping volume in the situation I describe is obviously associated with green speed. These experiments are not that hard to do; one could generate some kind of data about green speed and could make it show whatever one wanted to, if one planned it right, because there are a lot of factors that influence green speed! So why is it so difficult to find data about Si and green speed? I still think it is ridiculous23 that a stiffer leaf would make for a faster green speed.
This chapter is an updated version of this post from 2017 (https://www.blog.asianturfgrass.com/2017/06/i-dont-really-need-to-show-any-data-for-this-to-be-certain.html). The conversation started as a simple inquiry about the Pelzmeter, and somehow ranged all the way to clipping volume.↩