December and January DLI in Everglades City, Florida

I've been reading about the rains and clouds in South Florida and how extraordinary the past couple months have been. I saw these charts from Travis Shaddox, and I wondered what the light would be in photosynthetic units.

I downloaded monthly summary data since March 2007 for Everglades City from the NOAA. I use these data because they include global solar radiation, and I converted from energy units of MJ/m2 to photosynthetic units of mol/m2 using the 2.04 conversion factor of Meek et al.

This shows the average daily light integral (DLI) each month. One can see the seasonal changes, and one can also see that December 2015 had the lowest DLI of any December and that January 2016 had the lowest DLI of any January. I plotted all the data I could get, which is since 2007; I don't know what the values would have been before that. In the past decade, though, these were the lowest.

image from farm2.staticflickr.comLooking just at December and January year by year, January 2016 really stands out for having a low DLI. Blue triangles are December DLIs and red circles are January DLIs; the vertical dashed lines (blue for December, red for January) show the averages prior to Dec 2015 and Jan 2016.

image from

In a normal year at Everglades City, January would have more photosynthetic light than December. For seven out of the past eight years, the month of December had a lower DLI than January.  Only 2014 had a lower DLI in January than in December. But January 2016 is a big outlier; not only does January 2016 have the lowest DLI of any of the previous Januaries, but it also has a lower DLI than any of the previous Decembers.

The R&A Seminar on Sustainable Golf Course Design, Renovation and Maintenance in Asia

There are a lot of seminars happening in Asia in early March. Two new events are available this year, one in China and another in Thailand. These are The R&A Seminar on Sustainable Golf Course Design, Renovation and Maintenance in Asia.

The first is on March 3 and 4 in Beijing:

The R&A is to host a free to attend seminar in China that promotes responsible and practical approaches to golf course design, renovation and maintenance - highlighting the ongoing work of the industry in raising the expectations for golf.  This seminar will provide the most comprehensive sustainable education event in Asia across golf developments, renovations and course management.

The R&A Seminar on Sustainable Golf Course Design, Renovation and Maintenance in Asia will be held in Beijing on 3 and 4 March, as part of the China Golf Show at the National Convention Centre.


The second is on March 10 in Thailand, focusing on "golf developments, renovations and course management."

The R&A Seminar on Sustainable Golf Course Design, Renovation and Maintenance in Asia will be held at the Amata Spring Country Club on 10 March.

Both seminars are free to attend.

More information and registration for the China seminar is here: registration closes on February 26.

Details and registration for the Thailand seminar are here: registration closes on March 4.

Monthly Turfgrass Roundup: January 2016

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

Paul Jansen with a top 100 list of courses you may not have heard of but must play:

Edwin Roald on seven health benefits of golf.

Photosynthetically active radiation for 365 days at Tokyo.

Tokyo 2015 avg PPFD by hour and DLI

Handouts from the Northern Green Expo about turf nutrition, water, and light.

Zoysia tennis courts at Kawana:

Kreuser on simplifying soil test interpretation for turf.

Can one calculate how much water is required for a given area? Yes, here's how.

Growth potential (GP) and growing degree days (GDD): are they comparable?

Jason Haines with this report of 2015 pesticide use.

Breeden, Brosnan, and Vargas on how turfgrass herbicides work.

Haines on the best time to irrigate putting greens.

Course conditioning guidelines for PGA TOUR tournaments.

Albert Bancroft using a sandpro to help melt snow on greens:

Water quality for irrigation, questions and answers.

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.

A little more about tournament conditioning guidelines

After I shared my answer to the question about PGA TOUR conditioning guidelines, I received some feedback by email and take this opportunity to share more information on this topic.

First, Jim Prusa wrote:

The Tour course preparation guidelines are updated every few years. And those of the LPGA, Asian Tour are just about verbatum to the Tour's. The PGA Tour was the first to wisely establish guidelines after Dean Beman hired Allan MacCurrach as the first championship agronomist. Prior to, it was a weekly, conditioning crapshoot on the Tour subject to egos of clubs and supers. Here’s a whole piece on the subject FYI:

The guy on your blog was asking for “a rule of PGA tour course setting,” but there are no rules and only the guidelines as you properly provided to him. They are subject to a degree of application by experienced agronomists — and the the agronomists of the professional tours are the most experienced experts in the world ... I get worried when average golf course greenskeeper / supts consider duplicating PGA Tour conditions as hard and fast ‘rules.’ A little bit of information can be dangerously injurious in the wrong hands. Hope you can point this out to this fellow so he can caution others too as they also glean good info from the Tour’s guidelines.

Then, Cal Roth sent some more details:

They are exactly that, "Guidelines". Micah, each week on all six Tours now, we work with the advance team of Agronomist and Rules Official to pre determine set up for that specific course, based on the tournament expectations, course conditions, grass types, weather pattern, staffing level and talent, equipment availability, etc. Although our general efforts are focused on firm, dry playing conditions, this is relative to many factors. As example, we typically play tournaments with green speeds ranging from 10.5' to 13.5' depending on a lot of different factors. We have actually played on 8.5' when the wind is howling.

Is the leaking barrel analogy irrelevant?

I don't see how it helps in turfgrass maintenance, and I said so at the Northern Green Expo.

Liebig's law of the minimum says that growth is controlled by the level of the most limiting nutrient. Because there are 14 essential mineral nutrients, one could think that any of those elements might be limiting. But in practice, nitrogen (N) supply controls growth.

For more about N and growth, nutrient uptake, and nutrient demand, see Kussow et al. on Evidence, regulation, and consequences of nitrogen-driven nutrient demand by turfgrass.

After recognizing that N supply controls growth and nutrient demand, it follows that one can ensure the grass has enough of each element by keeping each above a minimum level and then adjusting growth as required with nitrogen.

These three articles explain how this approach can be implemented:

"What would you advise is the best course of action"

Another inquiry:

What would you advise is the best course of action with;

1) Bicarbonates in irrigation water
2) Ca, Mg etc in water that makes the water hard??
3) How do you soften the water?

Bicarbonate is not a problem. Don't worry about it. For more, see this or this.

Hard and soft water is not how one should think about irrigation water for turfgrass. Rather, I would look at this, this, or this. The main things to check are the salt content of the water (given as the ECw or the TDS) and the sodium adsorption ratio (SAR).

"I need a rule of PGA Tour course setting"

A greenkeeper sent me this inquiry:

I have a favor to ask of you. I need a rule of PGA tour course setting. Because I will presentation  PGA tour course setting in my office. So I search for rule .. but i didn't find clear reference.

I think the references in question are on this informative PGA Tour Agronomy page. Specifically, click the Tournament Prep tab, and then the PGA TOUR tab, and then download the Course Conditioning Guidelines document. A couple years old, but should be good enough for making a presentation in the office about PGA Tour conditions.


Understanding how turfgrass herbicides work

Selection_067This is a fine guide from Breeden, Brosnan, and Vargas at the University of Tennessee: Understanding how turfgrass herbicides work. It's about herbicide active ingredients and the associated mechanism of action class for those herbicides. It's important to know this so herbicide mechanism of action can be rotated. This is something you want to do before a problem develops. From the guide:

"Developing weed management programs utilizing herbicides that employ different mechanisms of action is critical to both preventing and managing herbicide resistant weeds. It is recommended to rotate herbicides that employ different mechanisms of action as often as possible, as well as implementing cultural practices that maximize turf competition and limit weed encroachment."

This guide lists the mechanisms of action and tells you how to do it. One to add to the #TurfReads list and to keep handy as a reference.

GP and GDD: are they comparable?

Someone asked me at the Northern Green Expo if the temperature-based growth potential (GP) and temperature-based growing degree days (GDD) are comparable. They sort of are, with a couple of exceptions. Comparable, yeah, kind of. But they are not interchangeable.

I downloaded the weather data for every day in 2015 from the international airports at London (Heathrow), Minneapolis, Sydney, and Tokyo (Haneda). Then I calculated the GP, and the GDD, and I made the charts shown in this post. The script to download the data and produce the charts is here . I’ll try to explain this, but I think it is easiest to see how GP and GDD are similar, and how they differ, by making some comparisons yourself.

First, here are the mean daily temperatures in 2015. The points are daily mean temperatures for each day of the year, and the lines are a moving average. Sydney and Tokyo are both hot in the summer, Minneapolis is coldest in the winter and hotter than London in the summer, and London is coolest in the summer but has winter temperatures close to those of Tokyo.

4 cities, temperature in 2015

Those cities have fairly diverse temperature ranges and variation in temperature from winter to summer. One expects a different growing environment in each. The GP3 is a value with a minimum of 0 and a maximum of 1, showing the expected limitation (or potential) of temperature on growth.

4 cities, GP in 2015

What do we see there? It’s a bit different than the temperature. Looking at the moving average for each city, we see Tokyo has a big drop in mid-summer because it is too hot, and Sydney has a substantial drop too, and Minneapolis has a slight drop in GP during the hottest summer temperatures, and London has peak GP in mid-summer because the average temperature rarely exceeds the optimum growth temperatures.

In the winter, the GP3 drops to almost 0 at Minneapolis, London, and Tokyo, but at Sydney it drops just below 0.5 in mid-winter, indicating that C3 grasses should still be able to grow, albeit slowly.

That was GP through the year. Now we can look at GDD0 . That is, for each day with an average temperature above 0°C (32°F), I take that temperature and call that the GDD. In this case, I would be using a base temperature of 0°C. This is the basis for the growing degree day model of Kreuser for the reapplication of plant growth regulators.

4 cities, GDD0 in 2015

That’s not exactly like the GP plot above. It is like zooming in on the temperature chart, but only showing the portion of the chart with temperatures above 0°C. Compared to the GP chart, one notices that with GDD 0 there is no drop in mid-summer when it is too hot, and the GDD0 does not drop all the way to 0 in winter at Tokyo and London.

So far it seems the GP and GDD are sort of the same, and sort of different. Both are based on temperature. But GDD is a measure of heat accumulation. GP is generating a value with a minimum of 0 when temperatures are far from an optimum for photosynthesis, and then generating a value that gets closer to 1 as the temperatures get progressively closer to 1.

There are various ways to calculate the heat accumulation through growing degree days. The GDD10 only counts the degrees on those days when the average temperature is above 10°C (50°F). This is GDD with a base temperature of 10°C. That makes sense for some things, and this chart of GDD10 is similar to the GDD0 chart in that it is as if the temperature chart were cropped to omit all values less than 10°C.

4 cities, GDD10 in 2015

That’s what GDD10 is showing. Now we are looking only at the days in the year when the average temperature was above 10°C, and we can see how much heat accumulation there would be each day.

The big difference between GP and GDD is evident, because Sydney and Tokyo are peaking in GDD when temperatures are at their hottest, but GP would produce a value less than 1 when GDD was highest in those places, because the temperatures are considered too hot for optimum growth of C3 grass.

GDD is heat accumulation. GP is optimum growth temperature accumulation. Let’s look at the accumulation explicitly, by adding together the GP for every day of the year in order to get these lines showing the cumulative sum of GP in 2015.

4 cities, cumulative sum of GP in 2015

Sydney with the year-round growth, although with a dip in winter and also a dip in summer, has the highest sum of GP. Then Tokyo, and Minneapolis and London are similar.

We can do the same type of chart for GDD0 .

4 cities, cumulative sum of GDD0 in 2015

Sydney still has the highest sum, then Tokyo, but there is less of a distance between these two cities than with GP, because GDD is using all of Tokyo’s hot summer days, but GP in Tokyo drops when it is hot. London and Minneapolis are similar again, but notice that Minneapolis accumulates almost all its GDD0 from April to October, while the milder winter in London allows the GDD0 to accumulate slowly year-round.

The cumulative sum of GDD50 is just a little different.

4 cities,cumulative sum of GDD10 in 2015

Now Tokyo catches and exceeds Sydney in the northern hemisphere autumn, but Sydney catches up quickly as summer approaches. And when counting the heat accumulation now only above 10°C, Minneapolis now has a lot more of that than does London.

The GP and GDD with various base temperatures (0 and 10°C are two of the standard ones) can be used for different things. GDD is good for things that are heat dependent. Growth regulators, insects, diseases, weeds – certainly the growth of certain plants in the range of temperatures from the minimum temperature required for growth up to the optimum temperature for growth. The GP is formulated in a different way, where it decreases when it is too cold or too hot for optimum growth.

We can look at that a little more closely. Now let’s just look at 2 cities to reduce the overlap: London and Minneapolis. Here is the GDD0 for every day of 2015.

2 cities, temperature vs GDD0 2015

That’s a linear increase in GDD0 for every increase in temperature above 0°C. If we would plot GDD10 , there would also be a linear increase with temperature, but the line would start going up at a mean daily temperature of 10 rather than at 0.

The GP for that same range of temperatures at London and Minneapolis looks completely different.

4 cities, temperature vs GP in 2015

That’s because the GP has a minimum of 1 and a maximum of 0, and the value is dependent on how close the temperature is to the optimum temperatures for photosynthesis.

Now to get back to the original question, after all those examples, are GDD and GP comparable? For them to be comparable, there would have to be a linear relationship (or almost linear relationship) between the accumulated GP and the accumulated GDD through the year.

Here I’ve plotted just that; the cumulative sum of GP for 2015 is on the x-axis, and the cumulative sum of GDD0 is on the y-axis.

4 cities, gp vs GDD0 in 2015

Well, that is sort of linear, but has a few weird curves or shifts. London’s GDD goes up in winter when the GP is still low, and Tokyo’s GDD goes way up in mid-summer when the accumulated GP is increasing slowly. And the line for Sydney looks pretty straight by comparison, but we can take a closer look at that by checking GP vs GDD10 .

4 cities, gp vs GDD10 2015

Now we are looking at how GP accumulates through the year, and comparing that to how GDD10 accumulates. At some times of the year it is linear, but as temperatures get low or high, the slope of that line changes.

If you would make these calculations for data at your location, I think you would see the same thing and would see how GP and GDD are similar and how they are different.

For more information, see:

"How do you calculate how much water is needed for a given area?"

I received this inquiry last week:

"When looking at water quantity for a new golf course, you have to determine how much water is needed obviously so what I want to know is.
1) How do you calculate how much water is needed for a given area (the whole golf course?)
2)  I know you have to look at the driest year data and base it on that but I understand you have to measure how much a grass plant and soil will lose via Evapotranspiration so you know what you have to replace so what methods do you use to find this out?"

I suggest calculating a water budget for the location using the method described by Gelernter et al. with this supplement providing the details for the calculations.