Chapter 4 Units of measurement

4.1 Note about units

You’ll find various units of volume in this book. My first serious interest in this topic began at Keya GC in Fukuoka in 2013. At that time, I was thinking, and writing about clipping volume, in terms of liters per green.

That’s fine for a single location; if one knows the green sizes and what a normal or target clippin volume is for a particular green, then that is the easiest way to think about it. In fact, I still think about it this way today, but I don’t communicate it that way anymore. That’s because there are different green sizes, or fairway sizes, or portions of a sports field, or lawn sizes, or whatever one is measuring. For communication about clipping volume to people at another property, or to estimate a dry harvest yield, it is necessary to express the volume in terms of area.

In Japan it is common to express this in terms of liters collected per 100 m2 (L/100 m2).5 This measure works great for monthly totals. It would be common to have a monthly clipping volume from putting greens of 30 to 120 L/100 m2.

For daily clipping volume, however, one ends up using a lot of decimal points when expressing in these units. When I wrote a report about this in 2017, this chart reproduced in Appendix A shows a median clipping volume of 1.2 L/100 m2 and 50% of the measurements in a range from 0.67 to 2.2 L/100 m2. It’s not ideal to try to express the clipping volume and be using so many decimal points. It may be 1.2 today, 0.9 tomorrow, 0.8 the next day, skip a day of mowing because of rain, and then get 1.7.

This past winter I started expressing daily totals in units of mL/m2 which I much prefer, as explained in the next section.

And as for this book? Well, it is a work in progress. I’m going to convert all the units and charts to the units I’m using now. But for now, I’m publishing what I have.

4.2 Something new6

First, the new. I am going to start using a standard unit of mL/m2 to express the clipping volume. This is milliliters per square meter. I have previously used units of L/100 m2. This is an easy change to make. 1 L/100 m2 is 10 mL/m2.

Why the change? Because this gives a number for almost all measurements that will be between 0 and 100. Vigorously growing turf may be from 20 to 50 mL/m2. Haven’t mown for a few days? You may get more than 50 mL/m2. Under tournament conditions, one might have less than 10 mL/m2 from a double cut of the surfaces. Using a unit on a scale from 0 to 100 is easier because it avoids decimal points. And it expresses the volume per square meter, which is the base area unit I prefer.

When I was in graduate school, I read a paper (Monteith 1984) by John Monteith (https://en.wikipedia.org/wiki/John_Monteith)—you’ll recognize that name from the “Penman-Monteith” equation for evapotranspiration—entitled Consistency and convenience in the choice of units for agricultural science. Here’s his advice:

“How should an appropriate multiple or sub-multiple of a unit be chosen? When repeated measurements of a quantity are to be reported, it is worth looking carefully for a unit which will avoid the frequent quotation of unnecessary zeros or decimal points. For example, the mean weight of a cereal grain should obviously be reported as 38.2 mg rather than 0.0382 g or 38200 μg. In general, when a quantity is quoted to two or more significant figures, the choice of unit should preferably allow its numerical component to fall between 1 and 100; but when only one significant figure is available, it should normally lie between 1 and 10.”

I try to work with units that fall in that range, and I intend to start doing so in my discussion of clipping volume.

References

Monteith, J.L. 1984. “Consistency and Convenience in the Choice of Units for Agricultural Science.” Experimental Agriculture 20: 105–17. https://doi.org/https://doi.org/10.1017/S0014479700000946.

  1. The unit of L/100 m2 is roughly equivalent to quarts/1000 ft2.↩

  2. This is from a blog post in March 2018 (https://www.asianturfgrass.com/2018-03-25-clipping-volume-green-speed-and-units/), in which I explained that I would start expressing clipping volume in units of mL/m2 rather than the unit of L/100 m2 that I had used previously.↩