## Energy for growth, and weeds

##### 29 September 2015

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

##### 28 September 2015

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.

## An easy PAR

##### 24 September 2015

That's the title of my column in the September/October issue of GCM China. I wrote about light:

"It isn’t that difficult once one understands the terminology and the units of measurement. There are just three technical terms to learn, and after that, it is all quite clear."

Those terms are:

• the light grass can use is photosynthetically active radiation (PAR)
• to find out what PAR is at any moment, one measures the photosynethetic photon flux density (PPFD)
• to measure PAR for a day, add up all the PPFD from sunrise to sunset to get the daily light integral (DLI)

## Multifunctional golf facilities: a handbook and an article

##### 22 September 2015

"During the spring of 2015, the multifunctionality of two golf courses in the Stockholm region were studied. 30 different activities were identified on and around the two golf courses!"

If that sounds interesting, check out these two new documents from STERF explaining more about their multifunctional facilities project:

## 'Tis the season

##### 19 September 2015

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.

## Indices of temperature and light and their relative effect on turfgrass

##### 18 September 2015

These values are calculated from the daily weather data in 2014 at Holly Springs, Mississippi:

• the temperature-based growth potential for cool-season (C3) grass, labeled here as gpC3
• the temperature-based growth potential for warm-season (C4) grass, labeled here as gpC4
• the daily light integral (DLI) divided by the maximum possible DLI on that day, labeled here as dli_index

Each of the three values have been calculated for each day of 2014. That gives 365 values for gpC3, 365 for gpC4, and 365 for the dli_index.

These histograms, with the breakdown of what values were for these three calculations,  show why I say that variations in temperature affect growth more than variations in light.

For the DLI index, there are few values around 0, and many above 0.75. There are about 90 days for C3, and more than 150 for C4, with a growth potential of about 0.

## A DLI Index

##### 16 September 2015

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.

If 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.

So 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.

The 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 $DLI_{max}$.

Rather 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.

This 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

##### 13 September 2015

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.

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.

Looking 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.

There 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.

Looking 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.

These 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

##### 10 September 2015

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.

The 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.

Watkinsville 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.

The 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?

## Monthly Turfgrass Roundup: August 2015

##### 09 September 2015

Here's a roundup of turfgrass articles and links from the past month:

Jim Brosnan wrote in the Green Section Record about Golf's most common weed control challenges.

From an award-winning superintendent blogger, a summary of everything that's interesting.

Typhoon damage on the Tuesday of tournament week at the KBC Augusta tournament in Japan:

Typhoon Goni has arrived in full force. Winds still very strong. Hope to start clean up this afternoon. #KBCAugusta

Posted by Keya Golf Club Turfgrass Maintenance on Monday, August 24, 2015

Video of typhoon and cleanup on KBC News:

Posted by Yuka Takagi McDaniel on Tuesday, September 1, 2015

After a prodigious effort by the maintenance staff and volunteers, the course was ready:

A list of MLSN articles in Chinese, English, and Spanish.

I wrote about soluble salts and K.

This is what a sod plugger looks like:

Temperature and light data from Alaska and Hawaii to show two extremes.

I put together a photo album of turf and animals, which I'll add to periodically.

Video of iron and soil pH layers from Glen Obear:

For more about turfgrass management, browse articles available for download on the ATC Turfgrass Information page, subscribe to this blog by e-mail or with an RSS reader - I use Feedly, or follow asianturfgrass on Twitter. Link and article roundups from previous months are here.