Combining temperature and light to compare location effect on turfgrass growth

The daily light integral (DLI) is the total amount of photosynthetically active radiation (PAR) at a location in one day. The DLI in an open (full sun) area changes with the latitude, time of the year, and cloud cover. There will be further reductions in DLI if there is shade from trees, structures, or mounds/mountains.

Nitrogen supply, plant water status, the DLI, and temperature all influence turfgrass growth, or even the ability of a particular species of grass to provide the desired surface conditions at a given location. With professionally-managed turf, the nitrogen and the water are controlled by the manager, so it is the DLI and the temperature left as the major factors, outside of the manager's control, that will influence the turfgrass growth.

I showed the distribution of DLI and how it differs from place to place. The implication of that, for ultradwarf bermudagrass, is that the place with higher DLI will be more suitable for the grass, and the place with lower DLI will require more actions to improve turf performance in shade, such as increasing the mowing height and reducing the N rate.

I was curious about the combined effect of temperature and DLI, so I looked up data for a few more locations. I'll make a series of posts about this, in each one describing what I've done. The previous distribution of DLI looked at Tokyo, and then Tokyo and Watkinsville, Georgia (near Athens), on the days in 2014 when the mean daily temperature was greater than or equal to 20°C (68°F). I pick that temperature because I expect ultradwarf bermudagrass can grow relatively well above that temperature, and will grow quite slowly below that temperature.

This chart shows Fukuoka, Tokyo, and Watkinsville, which had a similar number of days above that temperature in 2014 -- 150, 150, and 151 respectively. 3cityDensity

The distributions of DLI at each of these locations show that Fukuoka and Tokyo have more days with DLI less than 20, and Watkinsville has more days with DLI above 40. The median DLI at Watkinsville was 42.1, at Tokyo it was 35.8, and at Fukuoka it was 31.8.

What about the total DLI over the year? Rather than my arbitrary cutoff at 20°C, one can also add the DLI through the year. This chart shows the cumulative daily sum of DLI at these same 3 locations.


The cumulative sum of DLI was 9,139 at Fukuoka, 10,135 at Tokyo, and 11,736 at Watkinsville. Over the course of the year, there was more PAR at Watkinsville than at Tokyo, and more at Tokyo than at Fukuoka. This will have some impact on how ultradwarf bermudagrass would grow, and also on how the grass should be managed at each location.

What about temperature? I added together the temperature for each day at these same three locations, and the temperature doesn't vary as much between locations as the DLI did.


By adding together the temperature for each day, by the end of the year, Fukuoka has the highest total, then Tokyo, and then Watkinsville. The median annual temperature was 17.8 at Tokyo, 17.7 at Fukuoka, and 16.6 at Watkinsville.

With PAR, as represented by DLI, Watkinsville was highest, and Fukuoka was lowest. With temperature, as represented by the cumulative sum of daily mean temperatures, Fukuoka was highest, and Watkinsville was lowest. Can these be combined to get an index of growth, or an index of light and temperature affect on growth? I think so, and I will share some more calculations, and add in data for some other representative locations, in future posts on this topic.


An easy technique for monitoring the growth rate

Selection_017"Greenkeeping, at its core, is about controlling the growth rate of the grass. To get the desired green speed, or the maximum disease resistance, or the fastest divot recovery without too much thatch production, one must adjust the growth rate of the grass. An easy technique to monitor the growth rate is to measure the clipping yield from golf course putting greens."

That's what I wrote at the start of my turfgrass talk column in the July/August issue of GCM China. And I went on to explain just how easy this is, and more about why having a measurement of yield can be so useful.

"Beware! These topics are misleading and irrelevant"

Last week I led a seminar entitled "A discussion mostly about the principles of turfgrass nutrition, with a focus on soil nutrient analyses and their use in modern turf management." The slides for this seminar are available in English and in Japanese.

I usually talk about how one should do things, but in this presentation, I spoke for a while about how not to do things, with the list on this slide:

Why are each of these misleading and irrelevant?

The concept of locked-up nutrients
Nutrients in the soil may be relatively more or less available, but that is what a soil test evaluates. After a soil test (and a technical term for that is a nutrient availability analysis) has been conducted, one compares the test result to a guideline level. I recommend using the MLSN guidelines. Once the test is done, and the results are compared to the guideline, one knows the availability. That is all one needs to know. If nutrients are locked-up to the extent that the plant can't use them, that will be evident on the soil test result.

Focusing on what an element does, rather than how much is present
Phosphorus is crucial for root development, potassium is key to stomatal regulation, magnesium is at the center of the chlorophyll molecule, and calcium is essential for cell wall structure. All true, but also beside the point. What is important is that there is enough of each of those elements, not what those elements do. If there is enough phosphorus, all the root development benefits will proceed as they should. And so it goes for the other elements. The important thing to focus on is the quantity of elements available. Soil testing, and comparing the results to the MLSN guidelines, does just that.

Looking at percentages of elements rather than quantities
The quantity of an element available is what is important, and that will be expressed as either a concentration in the soil (for example as parts of element per million parts of soil -- ppm) or as a mass of element per surface area (for example as g m-2). Percentages of elements, or ratios of elements, don't provide the necessary information, and are not how one should look at soil test results. For more, see Nutritionism by John Foy and this review on cation ratios.

Water or saturated paste extracts to look at availability
The information in a water extract of soil is already contained in the standard (for example, Mehlich 3 or ammonium acetate extractant) test result. Take the same identical soil, divide into two sub-samples, modify the water soluble nutrients in one, and not the other, and then perform a regular soil test. The test results will show how the water soluble nutrients differ from one sub-sample to the next. A regular soil test already provides all this information. Water (or saturated paste) tests are good for research or for assessing soil salinity. They are not useful for determining how much fertilizer to apply. Carrow et al. wrote about this and offer this advice: "SPE [a saturated paste extract] is not the best method for determining soil fertility levels and can be very misleading."

The idea that an element can be exchangeable but not available
This is an insidious combination of 2 errors listed above: thinking of locked-up nutrients and the misuse of water extracts.

That's enough about how not to do it. For more about how to do soil testing, determine nutrient availability, and calculate how much fertilizer to apply, see:

Seeking input: GEO's proposed international voluntary sustainability standard for 'New Golf Developments'

The Golf Environment Organization (GEO) are seeking input from interested parties on their new golf development criteria. This is an exciting project, and you can read all the details here.

I encourage you to review the draft criteria for new developments and then send your comments to GEO. All the background and scoping information, the draft criteria, and the comments form are available at the new developments public consultation page on the GEO website.

Is ________ an essential practice, or a waste of time?

That's the question Bill Kreuser asked about syringing to reduce the temperature of cool-season turf during periods of extreme heat stress.

He prepared this document with a nice summary of the topic. Spoiler alert: "Does syringing help? Unfortunately, the answer is most typically no."

For more about syringing and irrigation, see:

How windy was it in St. Andrews yesterday?

It was exceptionally windy. I don't have data specifically for St. Andrews, but I was able to find data from RAF Leuchars, just across the Eden Estuary from the Old Course at St. Andrews.

I downloaded (from Weather Underground, as described here), the daily wind speed data for every July day since 1 July 1996. That is, 607 July days from the start of July in 1996 through 18 July 2015. Twenty years of July days.

In these 607 days, yesterday had the highest mean daily wind speed, 42 km/h, by a wide margin. In fact, the next closest day had average wind speed of 32 km/h.

MeanDailyFor the maximum sustained wind speed, which I think is the average across a 2 minute period, there were only three July days, out of the past 607, which exceeded the 55 km/h of yesterday.

MaxSustainedFor the maximum wind gust, not every day has a record for that. For the days with a maximum wind gust record, there was only a single July day exceeding the 80 km/h gust of yesterday.

MaxGustThese box plots below show all the data. The mean wind speed, maximum sustained wind speed, and maximum wind gust speed for 18 July 2015 are shown as red triangles.


These data, from the most recent twenty years, show that the wind speeds of 18 July 2015 were extraordinary.


Distribution of daily light integral (DLI) at Tokyo and Watkinsville in 2014

I discussed photosynthetically active radiation during a seminar this week in Tokyo.

This slide showed the distribution of the daily light integral (DLI) in Tokyo during 2014 on days with an average temperature greater than or equal to 20°C.

I mentioned that one could make an overlay of the distribution of DLI at other locations, and that a distinctive feature of the Tokyo-area climate is that there will be more days with a low DLI than at locations with a similar temperature in the southeastern USA.

In this plot, I show the density of DLI in 2014 for Tokyo and Watkinsville.


The temperatures in these locations were similar in 2014; the mean of the mean daily temperatures was 16°C in Watkinsville and 16.8°C in Tokyo. There were 151 days in 2014 with mean daily temperature >= 20°C in Watkinsville; Tokyo had 150 such days.

For the DLI on those days, however, there is quite a difference. The median DLI for those 150 days in Tokyo was 35.8, compared to 42.1 in Watkinsville.

Seminar on the fundamentals of turfgrass maintenance

Yesterday I gave a private seminar in Tokyo on the fundamentals of turfgrass maintenance.

I spoke about how I define greenkeeping, the four factors that influence growth, some specific challenges of turf maintenance related to the climate of Japan, and the fescue playing surfaces at the recent U.S. Open at Chambers Bay.

The slides for this seminar are available in Japanese or English.