A chart of PPFD at two locations this year from January 1 through last Friday

The photosynthetically active radiation (PAR) changes through the day and through the year. The PAR is measured instantaneously for a duration of 1 second as the photosynthetic photon flux density (PPFD), and by adding up the PPFD for all the seconds in the day, one gets the daily total of PAR, which is called the daily light integral (DLI).

These charts show the average PPFD on an hour by hour basis. With a look at a chart like this, one can see:

  • how length of the day affects PAR, by looking at what time in the morning and what time in the evening the PPFD goes to 0.
  • how time of the day affects PAR, by looking at the change in PPFD hour by hour through the day.
  • how day of the year, and consequently sun angle, affects the PAR, by looking at the maximum values of PPFD at midday and seeing how they change through the year.
  • how clouds reduce the PAR, by comparing PPFD on sunny hours or days to PPFD on hours or days that don't have full sun. For more about sun and clouds and time of year, see these descriptive slides with data from 4 days in Tokyo this year: a sunny summer day, a very cloudy summer day, a sunny autumn day, and a partly sunny autumn day.

This chart shows, for every hour of this year through last Friday, the average PPFD for that hour at Tokyo (red) and at Watkinsville (blue). Each panel of the chart is a single day, and the DLI in units of mol m-2 d-1 is written on each panel, in red for Tokyo and in blue for Watkinsville.

image from www.flickr.com

There have been 296 days this year, through October 23. On one of these days, February 10, there were erroneous data at Watkinsville, so I don't have a DLI. That leaves 295 days with a DLI for both Tokyo and Watkinsville. These locations have similar temperatures, and similar latitudes. How do they compare for photosynthetically active radiation? There have been 115 days with a higher DLI at Tokyo than at Watkinsville, and 180 days with a higher DLI at Watkinsville than at Tokyo.

I've made a couple other similar charts. This one shows the average PPFD at Tokyo hour by hour this year through October 12. Because the chart shows data for only one location, I've used color to indicate the month.

image from www.flickr.com

And the next one is the same location and dates as the above, with the addition of the DLI written on each panel.

image from www.flickr.com

The Watkinsville data are from the US Climate Reference Network and the Tokyo data are from the Japan Meteorological Agency.

Why light is more important for ultradwarf than for bent: my presentations at the Japan Turf Show

I'm giving two presentations at the Japan Turf Show in Tokyo this week. In the first one, I explain why light, by which I mean photosynthetically active radiation (PAR), is more important for ultradwarf bermudagrass than it is for creeping bentgrass. I use data from Tokyo and from Watkinsville, Georgia, to demonstrate this and to point out the difference in PAR between Japan and the region of the USA with similar temperatures.

The slides for this presentation about light are available in English and in Japanese.

In a second presentation, I talk about management of ultradwarf bermudagrass greens, explaining how this species performs compared to creeping bentgrass in Japan, and how it should be managed.

The slides for this presentation about ultradwarf management are available in English and in Japanese.

"I'd be applying potassium all the time": Part 2

In Part 1, I explained that adding potassium (K) after every precipitation event of 25 mm (1 inch) or more at Minneapolis or Fukuoka would supply from 2 to 13 times more K than the grass could use. Since there is no benefit to adding more K than the grass can use, it doesn't seem that such post-precipitation applications are necessary.

How can one determine how much K the grass will use? This calculator does, predicting how much K is required as fertilizer, all while making sure plenty of K remains in the soil as a buffer even beyond the K that is used by the grass.

And now, this calculator is available in a Japanese version too.


Energy for growth, and weeds

Two things today are kind of related to this topic. One is this -- Jim Brosnan mentioned, and showed photographic evidence, that "weed pressure on Oahu never ceases to amaze."

And I had a conversation with a golf course designer about fine fescue as an infrequently mown rough, in what climates that species can work, and what happens when it is too hot for fine fescue. And I mentioned that one can plant a number of species other than fine fescue in a warmer climate, but the problem becomes one of "how can we find a ball" because there is a lot of energy for growth. Of course there are various techniques turf managers can use to solve that problem, but then the turf will be alive, but thin. It must be if one is going to find a ball in it.

Once there are voids, weeds have an opportunity to grow. Turf managers can solve this problem too, with herbicides, or with manual removal of weeds. But now comes another problem. That is erosion, in locations with substantial rainfall.

Anyway, it must be that the growth of plants (desired species, and weeds) is related to the energy available for the plants to grow. In general the hotter it is, the more energy there will be for weeds, so when one thins a low maintenance rough, the energy for weed growth or invasion is going to be more in a hotter climate than in a cool one. I looked up some data from Japan -- hour by hour data of temperature and global irradiance for 2014 at Sapporo, Tokyo, and Naha. Then I converted the irradiance to photosynthetically active radiation (PAR) using a factor of 2.04.

I looked only at day time, when the sun was above the horizon. And I arbitrarily cut the data to look only at those hours when the temperature was greater than or equal to 20°C. Then I added up all the light, and all the hours. This is a very rough index of how much energy there is for growth, especially for the weeds that will grow when it is hot. And it is a conservative estimate, because the night temperatures influence growth too, and so does the actual temperature. This is just a quick way to note the differences between locations.

At Sapporo in 2014, the cumulative sum of PAR for hours when the temperature was greater than or equal to 20°C was 3,781 mol m-2. Tokyo has 5,844, and Naha was 9,124. Oahu is considerably warmer than Naha, so it almost certainly would have more PAR than Naha at this cutoff value.

Just looking at the time, how many hours were there for weeds to grow well in these different locations, by looking at how many hours there were with a temperature at or above 20°C? At Sapporo, there were 1,365 of these hours; at Tokyo there were 2,503; and at Naha it was 3,805. Again, locations in Oahu would almost certainly be more than Naha.

That is a real quick estimate of how much energy there is for weeds to grow, or more specifically how the energy is likely to differ in magnitude from location to location.

And one more thing -- in Scotland where a fine fescue rough actually works well, how much energy would there be for weeds? I don't have the exact irradiance data for Scotland, so I won't try to compare it to exact measurements. But I can give some idea of just how much lower the energy is, or how much lower the duration of time would be for weeds to grow rapidly. Huge disclaimer is necessary here, because the species are different, so a C3 weed like Poa annua might grow relatively rapidly in Dornoch but I am considering more the C4 weeds like Paspalum dilatatum or Cyperus rotundus.

It still makes an interesting comparison. Of Naha, Tokyo, and Sapporo, Sapporo is by far the coldest. And in the hottest month of the year in Sapporo, the average low temperature is 19.1°C, and the average high temperature is 26.4°C. How about somewhere in Scotland where fine fescue grows well? I picked Leuchars, just north of St. Andrews. In the hottest month of the year in Leuchars, the average low is 10.8°C, and the average high is 19.2°C.

A turfgrass recipe, with ingredients

Today I have two seminars at the 北海道グリーン研究会 autumn meeting. That's the Hokkaidō gurīn kenkyūkai -- the Hokkaido green research association. You can view or download the presentations and handouts at the links below.

The first presentation is called If turfgrass growth were a recipe, these are the ingredients.

There are four main factors (ingredients) that influence growth. These are temperature, water, light, and nitrogen. And one can either measure or control each of them.

Adjusting the growth rate of the grass is what greenkeeping is all about. And being able to measure and control the "ingredients" allows one to compare maintenance at one site to another, compare differences from year to year at the same site, and adjust inputs for different species. This provides a template for improvement of the turf through adjustments to the growth rate.

The second presentation is called How I would manage bentgrass greens today.

I explain how I would measure and control the ingredients of growth, and explain how I would do it differently today than I did 15 years ago when I was a greenkeeper managing bentgrass greens in Japan.

'Tis the season

Autumn is when one can find one of my favorite turf diseases -- elephant's footprint. Or at least this is my favorite name for a turf disease. It is found most often on unmown Zoysia japonica.

Al Bancroft shared a photo last week of what looks like early development of elephant's footprint.

 This is what the classic symptoms look like, further into autumn:


I was also reminded this week that real elephant footprints can be a turf problem too:

That's in Tamil Nadu, where one must beware of elephants.



For more about real elephant footprints on turf, see this turfgrass mystery.

A DLI Index

I've shown the sum of the mean daily temperature over 2014 for four locations: Fukuoka and Tokyo in Japan, Holly Springs in Mississippi, and Watkinsville in Georgia. Fukuoka had the highest accumulated temperature, then Tokyo, then Watkinsville, and the coolest of those four locations was Holly Springs.

Temperature2014If one were wanting to rank these transition zone locations for suitability of ultradwarf bermudagrass, the temperature is an important factor. Looking at temperature alone, it would seem that in 2014, Holly Springs would have been the worst of those locations for bermudagrass, and Fukuoka would have been the best for bermudagrass.

But the light available for photosynthesis needs to be considered too. The photosynthetically active radiation (PAR) is reported as the daily light integral (DLI). For these same four cities, the cumulative DLI in 2014 has Watkinsville the highest, then Holly Springs, then Tokyo, and last is Fukuoka.

RplotSo now, if one were ranking the locations by light, it would seem that Watkinsville would have been the best location in 2014 for ultradwarf bermudagrass, and Fukuoka would have been the worst.

The daily mean temperature can be represented as a value between 0 and 1 -- the temperature-based growth potential (GP). Plotting the cumulative sum of the C4 GP, one gets the same ranking of the locations at the end of the year, but on a different scale. Note another difference between the cumulative temperature and the cumulative GP plots.

GpThe slope of the GP plot is 0 (flat) when the temperatures are too cold for the grass to grow. This cumulative GP plot makes it easier to distinguish seasonal influence on growth than on the chart showing accumulated temperature.

Can the DLI also be expressed as a value with a minimum of 0 and a maximum of 1, like the GP? Yes. One can express the actual DLI ($DLI_{actual}$) as a fraction of the maximum DLI ($DLI_{max}$) for that day and location. I'll call that the DLI index, and it will be expressed on a scale of 0 to 1.

\[\text{DLI index} = \frac{DLI_{actual}}{DLI_{max}}\]

The $DLI_{max}$ varies based on latitude and day of the year. I've calculated a maximum DLI as 75% of the global solar radiation, as described here. The actual DLI will be the same $DLI_{max}$ on a perfectly clear day with no clouds. When there are clouds or other particles in the air that block some of the light from reaching the surface, the DLI will be lower than $DLI_{max}$.

HollyDLIRather than plotting the cumulative sum of DLI, one can plot the cumulative sum of the DLI index.


The cumulative DLI index plot gives the same separation at the end of the year as in the cumulative DLI plot, just on a different scale. Unlike the cumulative GP plot, the DLI index doesn't have times of the year with a slope of 0.

If it gets cold enough, grass will go dormant. That's what it means when the GP plot has a flat stretch. But DLI never gets that low. I've often been asked how to adjust the GP for light. And I usually respond that by explaining that temperature has more of an effect on turf growth than does light. So I usually prefer to just use the GP as an estimate of the potential for grass to grow.

But if one wants to make an adjustment to GP for DLI, a reasonable way to do it is to multiply the GP by the DLI index. For C3 grass, one may adjust the DLI index to account for the light saturation point. If we call the GP multiplied by the DLI index a growth index, it allows us to combine the light and temperature for a location to estimate their influence on growth.

Remember that by cumulative temperature, Fukuoka was highest, and Holly Springs was lowest. By cumulative DLI, Watkinsville was highest, and Fukuoka was lowest. By plotting the cumulative growth index, which combines temperature and light, Watkinsville is highest, then Tokyo, Holly Springs, and Fukuoka.

GrowthIndexThis plot is essentially taking the effect of temperature on growth and adjusting it for light, or conversely taking the light effect on growth and adjusting it for temperature.

One can easily compare relative differences between locations on a daily, weekly, monthly, or annual basis. With the ease of measuring DLI at different locations on a property using quantum meters, one can also use this growth index to demonstrate the effect of tree or structural shade.

Tournament week clipping volume

The KBC Augusta golf tournament is held the last week of August at Keya Golf Club near Fukuoka. The greens are korai (Zoysia matrella) and when the greens are mown, the volume of clippings is noted.


These data are collected not only during the tournament week, but throughout the year when the greens are mown.


I wrote more about this process in these posts:

Andrew McDaniel, the greenkeeper at Keya GC, shared the clipping yield data with me and I've summarized it in these charts.

The average daily clipping yield, plotted week by week through the year, shows that the grass starts growing at the end of March, reaches a peak in the hottest weather of July and August, before dropping down due to tournament preparations. This reduction in clipping volume is achieved by reducing the N rate, only adding irrigation to prevent dry spots, and applying trinexapac-ethyl.

WeekLooking just at August of 2015, one sees there were 4 days when the greens could not be cut due to heavy rain. One of those days was 25 August, the Tuesday of tournament week, when a typhoon came through. Not surprisingly, the clipping volume is larger on the day after a missed mowing.

AugOnlyThere was a downward trend through August, with the maintenance being done in a way that targets a clipping yield during tournament week of less than 1 liter per 100 m2 of green area.

Looking at clipping volume every day in 2015, it is even more clear when the grass starts growing in the spring, and also that the korai doesn't really grow until after the rainy season, when the temperatures increase. It is only in July and August when the grass is growing quickly. This chart also shows the days during the season when the greens could not be mown.

2015Looking at clipping volume for the 2013, 2014, and 2015 KBC August tournaments, one can see the 2014 and 2015 tournaments had less than 1 liter per 100 m2 from Thursday through Sunday. Based on measurements of green speed and evaluation of ball roll, the goal in 2016 will be to get the clipping yield down to the 1 liter level by the start of tournament week.

3yearsThese measurements don't take much time to collect and they can be useful in evaluating how the maintenance work should be adjusted to achieve the desired green conditions.


What about the work that was done to get this clipping volume, and the conditions produced?

  • On the greens at Keya GC, 8.5 g N and 3.5 g K/m2 since the start of 2015.
  • Mowing height for the tournament was 2.6 mm with the Shibaura 22 inch GEXE.
  • Except when adjusted due to weather, the greens were mown 2x each morning, then rolled with a Toro lightweight roller, and then were mown 1x at the end of the day.
  • Primo Maxx and soil surfactants applied to the greens.
  • Irrigation added as necessary to prevent dry spots.
  • Morning green speed during the tournament rounds ranged from 10.7 to 11.2 feet.

4 cities, 2 continents, and 1 year of light and temperature

I've added data for one more location -- Holly Springs, Mississippi -- to this analysis of light and temperature in 2014. Holly Springs in 2014 was a little cooler than Fukuoka, Tokyo, and Watkinsville, with 136 days at a mean temperature of 20°C or above. Fukuoka and Tokyo both had 150 such days in 2014, and Watkinsville had 151.

Previous posts on this topic include:

By adding together the mean daily temperature for each day of the year at these locations, one can see how much the total temperature is.

4temperatureThe temperature will have some effect on the grass. If we are thinking of ultradwarf bermudagrass, for example, it is expected that the locations with the higher temperatures will generally be better for the grass.

One can also look at the cumulative sum of the DLI.

4dliWatkinsville had a higher cumulative temperature than Holly Springs, but the cumulative DLI was similar at those locations in 2014. And Tokyo and Fukuoka, which had higher cumulative temperatures than either Watkinsville or Holly Springs, didn't have so much DLI.

Looking only at those days with a mean temperature greater than or equal to 20°C, one sees that the distribution of DLI for Watkinsville and Holly Springs have a lot more days with DLI > 40 than do Tokyo or Fukuoka, while Tokyo and Fukuoka have a lot more days with DLI < 20 than do Watkinsville or Holly Springs.

4densityThe next calculation I'll make is the development of a DLI index, which I'll calculate as the actual DLI divided by the maximum the DLI could be on that day at that location. From this, I'll be able to express both temperature (by calculating the growth potential) and DLI on a scale of 0 to 1. Then if I multiply those two values, will I have a useful growth index?

Temperature and light data from Fairbanks and Hilo for illustrative purposes

Temperature and light have a major influence on how ultradwarf bermudagrass will grow. I've shown the distribution of DLI at Tokyo and Watkinsville, and the DLI and temperature at Fukuoka, Tokyo, and Watkinsville.

Before going any further with calculations and combinations of light and temperature from transition zone locations, I thought it might be illustrative to show how these charts look for a couple non-transition zone locations -- Fairbanks, Alaska, and Hilo, Hawaii.

First, the temperatures. I've included Tokyo as a reference. Remember, Tokyo had an annual temperature, as represented by the cumulative sum of daily mean temperature in 2014, slightly more than Watkinsville, and slightly less than Fukuoka. All those cities, however, were pretty similar. Not so with Fairbanks and Hilo.

Temperature_3_disparateHilo has a tropical rainforest climate, and because the daily mean temperature is almost the same throughout the year, adding them together produces a straight line. Tokyo is the same as what was shown previously. And Fairbanks, where we won't be growing ultradwarf bermudagrass, has a cumulative daily mean temperature in 2014 that just barely stays above 0. The point of showing Hilo and Fairbanks is to point out what these charts would look like in a tropical situation, and in a subarctic one.

As an aside, one sometimes hears of ultradwarf bermudagrass being a big thatch producer, and requiring a lot of work for organic matter management. I would look at it differently, noting that any grass is going to grow at a different rate based first on the temperature and PAR at a location, and secondly based on the nitrogen and water supplied. Clearly, based on temperature alone, an ultradwarf bermudagrass would require no organic matter management in Fairbanks, because there would be no thatch production.

So Hilo is looking pretty good for ultradwarf bermudagrass, by temperature, and how does it look for light? Hilo is 19.7°N, Tokyo is 35.7°N, and Fairbanks is 64.8°N.

Hilo_disparate_dliInteresting. Fairbanks looks about like I would expect. That far north the DLI in winter is negligible. But how is it that Hilo just barely tops Tokyo for cumulative DLI? That's the effect of clouds, and it is why bermudagrass grows so poorly in Hilo. In fact, Watkinsville in 2014 had cumulative DLI of almost 12,000 -- more than the cumulative DLI in tropical Hilo.

I've mentioned previously the importance of light (DLI) when temperatures are close to an optimum for warm-season grass growth. The climate.asianturfgrass.com website has lots of charts and videos about that. 

In these recent posts, I've shown the temperature and the DLI separately. Coming up, I'll add one more transition zone location, and then see what happens when various combinations of DLI and temperature are made.