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December 2015
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January 2016

"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.

"Knowing which soil test results are important can simplify turf management"


Bill Kreuser's guide to soil test interpretation; read it! Here's how he describes it:

"While soil tests can be useful, their results are frequently overanalyzed and overinterpreted. Sometimes soil test results can be more confusing than helpful. It doesn't have to be so difficult. The goal of this publication is to explain which soil test values are important and which values can be ignored."

After reading the publication, I think it achieves that goal.

Presentation slides for my 5 talks at the Northern Green Expo

Here are links to the handout and the presentation slides for the 5 talks I gave at the Northern Green Expo. Topics? I tried to explain how I think of the four factors that influence turfgrass growth: light, water, temperature, and nutrients (of which nitrogen is used in the largest quantities by the grass). Then, I talked about how I would put this understanding to use in the day-to-day management of turfgrass.

First, with all the details, the 31 page PDF handout. If you are interested in these topics, I hope you'll read it.

Then the presentation slides, in the order they were delivered.

The (New) Fundamentals of Turfgrass Nutrition

Nutrient Use by the Grass and Nutrient Supply by the Soil

Calculating the Fertilizer Requirement for Any Turfgrass, Anywhere

Soil Water Management: Timing, Amount, and Syringing

Instead of Shade, Let's Talk About Light

My handouts for the Northern Green Expo

I'm giving five presentations at the Northern Green Expo.

  • The (New) Fundamentals of Turfgrass Nutrition
  • Nutrient Use by the Grass and Nutrient Supply by the Soil
  • Calculating the Fertilizer Requirement for any Turfgrass, Anywhere
  • Soil Water Management: Amount, Timing, and Syringing
  • Instead of Shade, Let's Talk About Light

I combined the handouts for each presentation into this single document for easy reading. I especially like this part:

Selection_060 Selection_061

Monthly Turfgrass Roundup: December 2015

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

“The R&A is proposing a new approach to golf green construction

Estimating daily light integral (DLI) in Tennessee.

Mike Richardson shared this useful chart with monthly DLI for 48 states in the USA.

How many in the turf industry use Twitter?

"One of the best places to study tropical grasses"

Dave Wilber asked, do you have a big "ah ha" agronomy moment?

Temperature and sunshine in the US and China.

An equipment wish list for a high-end facility.

What's a no problem DLI for warm-season grass on putting greens?

Frost and footprints -- coyotes and raccoons damage turf more than I ever imagined.

These two titles get it wrong.

Dave Wilber and Micah Woods talked on The Turfgrass Zealot Project.

That was fast. Before and after of a new bunker.

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 summary of photosynthetically active radiation for 1 year at Tokyo

image from
This chart (download it here) shows the average photosynthetic photon flux density (PPFD) for each hour of 2015 at Tokyo. The daily light integral (DLI) is the number written in black at the top right corner of each facet in this chart.

One can get some idea of how the DLI changes seasonally and with cloudy weather; one can also see how the PPFD changes from sunny to cloudy days at different times of the year.