"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.

• Download the article in Chinese
• Download the article in English

My turfgrass talk column in the May-June issue of GCM China explains how to calculate the amount of irrigation water to apply when one is trying to keep the soil salinity (EC_e) from exceeding a threshold value.

The article is available in both Chinese and English.

• Download the article in Chinese
• Download the article in English

If the salt is not leached, and accumulates in the soil, the grass can die. To prevent the accumulation of salt, more water than the grass can use must be applied. This causes leaching as the extra water moves below the rootzone, carrying some salt with it.

Good drainage is essential when salt in the irrigation water requires leaching to be done. In the photo below, there is a low area below the drain, and salt accumulation in the soil at that spot prevents grass from growing.

For more on this topic, see the preceding article in this series: Do you know how much salt is in your irrigation water?

My column in the March-April issue of GCM China is about salt. The salt in water is invisible, so one needs to test the water to find out how much salt is in it.

As I wrote in the article, water with total dissolved solids (TDS) of 800 ppm would add 56 g salt/m² (11.2 pounds salt/1000 ft²) in a 2 week period if irrigation is applied at 5 mm/day. Being aware of how much salt is in the irrigation water is the first step in determining if leaching will be required.

• Download article in Chinese
• Download article in English

The latest issue of GCM China is fresh off the presses, and it includes my article about four ways to optimize the root system on golf course putting greens.

The article is available in both Chinese and English.

• Download Chinese version, PDF
• Download English version, PDF

What did I suggest?

Mow the grass as high as possible, apply the right amount of N at the right time, make sure there is plenty of air in the soil, and avoid P deficiencies. Read the article for full details.

Penn G-2 creeping bentgrass in Shanghai

This chart shows the temperature-based growth potential for cool (C₃) and warm (C₄) season grasses at Beijing and Seoul.

It is too cold in winter for any type of grass to grow, and during the spring, summer, and autumn, C₃ species will grow more than C₄ species. Of course, C₄ species use less water than C₃ species, tend to be more salt tolerant, and in this type of climate, will require less mowing due to the shorter growing season.

Playing golf on a Zoysia japonica fairway near Seoul, March

Zoysia japonica is in common use as a fairway and rough turf around Seoul, more so than it is in Beijing.

Bentgrass greens and Zoysia japonica through the green near Seoul, March

Based on the similar temperatures between Seoul and Beijing, Zoysia japonica would certainly perform well in the summer in Beijing. But with colder winters in Beijing than in Seoul, one would need to be more concerned about potential winterkill. It would seem that Beijing winters would be almost too cold for Zoysia japonica, based on the temperatures at which this species was killed in this experiment by Patton and Reicher.

March golf near Seoul

The best bentgrass, bermudagrass and seashore paspalum playing surfaces will be produced when the soil has just enough water to keep the grass from wilting and the remaining soil pore space will be flled with air.

I wrote about this, and how it can be accomplished, in a column for GCM China. 

Measuring soil water to estimate soil air 

测量土壤水,估算土壤空气

"Sand is a terrible growing medium for plants," I wrote, in a recent article for GCM China. 

But I went on to explain why sand is used for high-traffic turf areas – because of its resistance to compaction and because of a high infiltration rate. However, those characteristics of sand are lost if organic matter, a natural result of grass growth, is not managed. 

The article, available in Chinese or English, gives the details, along with three steps one can take to ensure that the "desirable characteristics of the root zone will be maintained indefinitely."

Some years ago, on a fine December day, I was at this beautiful golf course in southwestern China. The tees, fairways, and greens are creeping bentgrass. From the tee, I had the view above. But when I got to the fairway, I was surprised to look down and see this pattern.

In fact, there were a lot of cup cutter plugs, lined up one by one, on this fairway.

The mystery is this: why are there cup cutter marks in the fairway?

The correct answer was given in quick succession by @GreatManDan and then soon after by @gossturf.

@asianturfgrass Hydraulic oil would be my first option.

— DG (@GreatManDan) August 19, 2014

@asianturfgrass @gord_mckie repairs to a hydro leak?

— Jason Goss (@gossturf) August 19, 2014

What I found especially interesting was just how many plugs it took to make this repair. The diagonal across the fairway was about 175 yards in length. With each plug 4.25 inches in diameter, that would require 1482 individual plugs to make the repair. 

Every turf manager knows that temperature has a huge influence on the growth rate of the grass. Consequently, mowing, fertilizing, overseeding, winter dormancy, heat stress of cool season grasses, and much more are all directly influenced by temperature.

I find it especially convenient to make use of the turfgrass growth potential (GP), a number between 0 and 1 that represents the proximity of the actual temperature to the optimum temperature for growth. The turfgrass GP was developed by Wendy Gelernter and Larry Stowell at PACE Turf, and their 2005 GCM article about GP is on my list of 5 articles every greenkeeper should read.

The turfgrass GP was the topic of my (turfgrass talk) column in the July/August issue of GCM China. In the article, I explained what GP is:

By expressing the temperature as a number between 0 and 1, we can get an idea of how much the grass has the potential to grow based on how close the actual temperature is to the optimum temperatures for growth ... At frst glance it might look complicated, but it is actually quite simple. There is a minimum value of 0 if the actual temperature is very different from the optimum growth temperature. A maximum value of 1 means the actual temperature is the same as the optimum growth temperature. The GP value, then, is simply a number that says how close the actual temperature is to the optimum temperature.

Download Turf growth and temperatures in Chinese or English.

The growth potential (GP) of cool-season (C3) and warm-season (C4) grasses varies between 0 and 1 based on the optimum growth temperatures.

If you would like to read more about GP, see:

• Turfgrass Nitrogen Requirement and Growth Potential
• Using temperature to predict turfgrass growth potential and to estimate turfgrass nitrogen use
• Growth Potential, Inflection Points, and an Optimum Temperature for Overseeding
• PACE Turf climate appraisal form (metric) with GP equation embedded
• PACE Turf climate appraisal form (US standard units) with GP equation embedded
• Understanding turfgrass nutrient requirements
• Are your greens reaching their full potential?, by Greg Evans
• Growth potential fertility: after 2 years, by Jason Haines

You can get the equation to calculate GP from temperature by downloading the climate appraisal forms above, or make the calculation yourself using the growth potential equation.

\[GP = e^{-0.5(\frac{t-t_o}{var})^2}\]

or, in an alternative formula to generate the same result,

\[GP = \frac{1}{e^{{0.5}(\frac{t-t_o}{var})^2}}\]

where,

GP is growth potential, a value from 0 to 1
e is the base of the natural logarithm, approximately 2.71828
t is the actual mean temperature
t_o is the optimum temperature, 20°C for C₃ grass, 31°C for C₄ grass
var is the variance which adjusts the shape of the curve, 5.5 for C₃ species and 7 for C₄ species when using °C.

If you want these equations already embedded in a spreadsheet, or want to use the Fahrenheit temperature scale, see the climate appraisal forms at the PACE Turf IPM planning tools. 

Related articles

Explaining the Turfgrass Growth Potential

Turfgrass Growth Potential: 4 cities, 472 days

Update 4 August 2014: In the latest announcement e-mail, Darry informs us that "You won’t want to miss this great opportunity to learn about turf, water and fitness ... never before has a program like this been assembled for our industry." I'll be speaking about the subjects mentioned below, David Paterson will be speaking about irrigation, and Mr. Antonio Barrias, the owner and head coach of CrossFit Cotai and CrossFit XVI, will be speaking about fitness and nutrition. And then, after the seminar, we will be in Macau, after all.

I'll be speaking about sustainability and leaves of grass at the South China Turf Managers Association (SCTMA) Educational Seminar on 15 August. This seminar, with a theme of Green Sustainability/Environment, will be held at the Sheraton Macau Cotai Central. If you would like to attend, please RSVP with Darry Koster, the SCTMA President. 

Last time I attended an SCTMA seminar, with Dr. John Kaminski and SCTMA President Darry Koster at Clearwater Bay GC

I'm excited to discuss these topics, first by explaining how sustainability can be more than just a word with a vague meaning. In turfgrass management, we have a certain area of managed turf, we apply some amount of water, pesticides, and fertilizer, and we use fuel and electricity in some amount. Documenting these inputs is the first step in measuring sustainability, and once these inputs are known, and tracked, it is often possible to reduce these inputs. Those reductions, if tracked on a facility by facility and year by year basis, will be more sustainable, by any definition of that term. 

The December 2013 GCM article by Gelernter, Stowell, and Woods will set the framework for my talk on Measuring Sustainability

In my second presentation, I will talk about turfgrass nutrient use, and will explain how we can look at the nutrients in the leaves to estimate the maximum amount of any nutrient that the grass can use. Once we have the estimate of that maximum amount, it is a straightforward calculation to determine how much of that nutrient needs to be supplied as fertilizer. This process is the foundation of the minimum levels for sustainable nutrition (MLSN) guidelines, which are designed to ensure that any turfgrass, in any location, will be supplied with all the nutrients it requires.