## Growth potential (GP) and optimum temperatures

##### 31 July 2014

Mark Hunt's Weatherblog had an interesting statement this week – "why I think the Growth Potential [Optimum] Temperature is wrong for Poa annua." Regarding recent temperatures in Southeast England, he wrote:

For me I think Poa has been under stress for the last two weeks and so the GP model should be showing this with a lowered daily figure, but it’s not and therefore I think the optimum temperature is set too high at 20ºC, it should be more like 18ºC, so that’s what I’m going to change to in 2015.

I think this is a good idea. The objective of the growth potential (GP) model is to generate a number between 0 and 1 that can be an index of potential to grow, or high temperature stress, or low temperature dormancy, and this can be adjusted to fit the conditions and grass species at a particular site.

Jason Haines wrote about his adjustment of the GP to 18ºC for Poa annua greens in Canada. When I was in Iceland last year, I wrote that the 20ºC optimum temperature in the standard GP equation would likely need to be adjusted to fit the observed growth under Icelandic conditions. One of the great things about the GP equation is the ease with which one can adjust it.

Growth potential (GP) curves shift left or right if one changes the optimum temperature in the growth potential equation

Now I don't advise changing this too much if you don't have to. The standard optimum temperatures of 20ºC for cool-season (C3) grass and 31ºC for warm-season (C4) grass work well for most turfgrass species. And it is the simplicity and consistency of the GP concept that makes it so useful.

With C3 grasses, I would consider adjusting the optimum temperature down if looking at Poa annua (as Mark wrote) or fine fescue (pictured above in Iceland). With C4 grasses, the only one I would adjust is kikuyugrass (Pennisetum clandestinum), which will have an optimum temperature somewhere in the mid-20s. Kikuyugrass thrives in temperatures warmer than optimum for C3 grass, but at much cooler temperatures than optimum for other C4 grasses.

For example, kikuyugrass is the dominant grass in the mild climate of Kodaikanal (above) in the Palani Hills of Tamil Nadu, just as it is at Real Club de Golf de Las Palmas (below). One would need to adjust the optimum temperature in the growth potential equation for this species in particular.

## Superintendents discuss the Global Soil Survey

##### 30 July 2014

The first year anniversary of the Global Soil Survey is coming up, and I've been doing a lot of work to analyze the data that has been collected so far. We have received samples from a wide range of soil and grass types. It is interesting to see how the data from these diverse turfgrass growing environments are distributed, and to apply the same analytical procedures that were used to develop the MLSN guidelines to these new data.

Over the next few months, I'll be working with Larry and Wendy from PACE Turf on an annual report with the first year results of the Global Soil Survey (GSS), an update to the MLSN guidelines, a presentation on these results at the 2014 Crop Science Society of America annual meeting, and a technical article about the MLSN guidelines and the supporting GSS.

Empirical cumulative distribution function for soil test phosphorus data from the ATC, Global Soil Survey, PACE Turf, and combined data sets

The process to develop these guidelines can seem a bit complicated, and I was pleased to see a recent article in Golf Course Industry with a simple explanation of the GSS. In the article, Larry Stowell was quoted with a great explanation of this project:

It’s really a common sense approach. We are just trying to develop some tools to make it easier for turfgrass managers to make the applications at the right rates they need to make.

This project is possible because of the many turfgrass managers, golf course superintendents, and golf clubs that have participated in this project by purchasing a kit and submitting data from soils that support good performing turf at their location. I was pleased to see that the article gave a chance for two superintendents who have participated in the survey to speak about this important topic. Here are a few quotes.

Matt Crowther, CGCS from Mink Meadows Golf Club, on fertilizer and one of the reasons he participated in the GSS:

If you’re not being regulated on [nutrients] right now, then you will be soon. It’s sweeping the country. I don’t see how there will be one section that gets away from it. To me, it only seems logical to show an interest in that and try to get ahead of the curve.

Akoni Ganir, from Tokatee Golf Club, on his participation in GSS and philosophy of product application in general:

It’s a very logical approach and aligns with the way I think. I feel like I’m not applying anything to the grass that’s unnecessary. I feel as a turf manager there is a purpose to all of my applications. I’m not putting ‘X’ or ‘Y’ product out there because someone said, ‘Try this because this is great.’ I know why I am putting everything down and for what reason.

This is an ongoing project, and the data collected will benefit everyone in the industry by identifying the nutrient levels that are required for good turf performance. The more sites we collect data from, the more useful the guidelines will be. If you would like to participate, and ensure that data from your growing environment is included in this exciting citizen science project, you can get your survey kit here.

I've had a chance to visit some of the courses that have joined this project, including beautiful Tama Hills GC in Japan (picture of the unique two green system, below). It is really cool to be able to make use of the data that are stored in the soils of every golf course or other turfgrass soil, to combine those data, summarize them, and from those data at actual sites with good-performing turf, to be able to generate guidelines and fertilizer recommendations that can be used by the entire industry. This is really an exciting project, many thanks are due to everyone who has participated so far, and I hope you will join this project so that data from your site can be represented as well.

Manilagrass and creeping bentgrass at Tama Hills GC near Tokyo

## A number between 0 and 1: using the turfgrass growth potential

##### 29 July 2014

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.

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

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
to 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

## Measuring Sustainability and Leaves of Grass

##### 27 July 2014

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.

## Tropical carpetgrass part 2: ugly duckling or swan?

##### 26 July 2014

When I wrote about tropical carpetgrass being an unappreciated grass, the conversations (1 & 2 & 3) that ensued showed a mixed response. Some people really like tropical carptegrass (Axonopus compressus), and others have no use for it.

Tropical carpetgrass on a golf course fairway in Singapore

It was rightly pointed out that in a a subtropical environment, tropical carpetgrass will not be ideal throughout the year, especially when it is cool. And like other grasses, there will be issues with drought tolerance, and traffic damage, and so on. Where this species is really well-adapted is in tropical climates that receive more than 1,000 mm annual precipitation; one wouldn't want this grass where precipitation is less than 800 mm. It is not a perfect grass, even in the tropics, but no grass is.

Tropical carpetgrass through the green at Chumpon, Thailand

So why do I persist in writing about tropical carpetgrass? Because for many tropical sites, this is the grass that should be used, and it has some very attractive characteristics that are especially relevant to the way I think about turfgrass management. When possible, I think we should manage turf with a minimum amount of inputs. Tropical carpetgrass, more than other species, can be maintained as a multipurpose turfgrass with the fewest inputs.

Last year I was interviewed by Matt Adams on the Fairways of Life radio show. You can listen to the interview here.

07.09.13 INT ARCHIVE Fairways Of LIfe Micah Woods_3592772

I was expecting Matt to talk with me about tournament preparation and golf and grasses around the world. Instead, he started by asking about maintenance inputs and grass selection:

Today more and more, there is pressure upon every golf facility in terms of how they maintain the golf course – the general line that we're hearing is that golf courses need to embrace more of the brown because water is at such a premium anywhere and everywhere around the world.

Then he asked, how can the type of grass chosen help us out in terms of maintainenance cost and availability of water? Rather than talking about using more resources and spending more money, the focus at the global level is to use less resources in turfgrass maintenance.

This was also a prominent theme of Don Mahaffey's recent conversations at Golf Club Atlas (first interview, second interview). These are really good discussions about what golf course maintenance should be about, and I highly recommend taking the time to watch both of them in their entirety. In the second video, Don said something that is very applicable to turf management:

We cut our maintenance expenses greatly, because we just focused on what's good for golf, and interestingly, no one complained.

Tropical carpetgrass fairway at Phuket, Thailand

With tropical carpetgrass, in a tropical climate with annual precipitation of at least 800 mm, and preferably with 1,000 mm or more, this grass requires only mowing. It can be maintained without fertilizer or pesticides, and irrigation is only required if one wants to make the grass green, or if the turf is to be heavily trafficked with golf carts.

There will be many golf courses or turf managers that prefer to grow and manage a grass that has different characteristics. But let's not forget about the many good characteristics of the multipurpose tropical carpetgrass. As the recent research from Trinidad and Nigeria demonstrates, this species has a number of advantages compared to other turf species in a tropical environment.

Tropical carpetgrass lawn in Ayutthaya, Thailand

## Baker Street Botany

##### 21 July 2014

I'll retire to my usual haunt to ponder this one. Let me set the scene.

Mid-July, Saitama prefecture, Japanese lawngrass (Zoysia japonica) at the back of a driving range, infrequent mowing, no recent drought, and no recent frosts. Looking down at the grass – for one must be observant – I saw horizontal bleaching or striping on the leaves.

"Aha," I said, "I've seen this before. At Okayama prefecture on the same grass species, in the same season. And I've seen this picture with almost identical symptoms on the same species grown in Florida."

Bleached bands on Zoysia japonica near Tokyo

I inquired about recent weather and drought and herbicide applications. Temperatures have been relatively mild. There has been enough rainfall to keep the grass from experiencing drought stress. The hottest day of the year so far was 1 June, with a temperature of 34°C. That was more than 6 weeks ago, and since then the temperatures have been mild.

Bleached band in the center of a Zoysia japonica leaf near Tokyo

Glyphosate was applied about a month ago, not to this grass directly, but in an immediately adjacent area less than 1 meter away.

Have you seen these symptoms on Zoysia japonica? If so, under what conditions do they appear?

Bleached bands on Zoysia japonica at Okayama

## "I noticed something crazy"

##### 17 July 2014

Jason Haines shared an interesting report about clover (or actually, the lack of it) on tees at Pender Harbour GC in Canada.

I noticed something crazy. All the clover on the tees had disappeared ... until 2005 we would spot spray these areas with Killex [2-4-D, MCPP, Dicamba] but haven't applied any type of herbicide since then. Today I could only find one small patch less than 1 m2 on my tee boxes. Crazy!

So what the heck happened to the clover? ... I was not trying to rid the tees of clover in any way. This was an indirect consequence of something that I did ...

Since 2012 I have really only applied nitrogen and wetting agents to the tees. This combined with the lack of liming has, in my opinion, led to the disappearance of the clover ... and the tees have never been better in the 13 years I have been here. Just nitrogen, wetting agents, and some aeration every now and again. No "weeds." Super quick divot recovery. As close to perfect as I can expect.

I was pleased and pleasantly surprised to find that this result had happened so quickly at Pender Harbour, and it reminded me of the results at the Park Grass experiment in 1857 and 1858, as reported by John Bennet Lawes and Henry Gilbert in their Report of Experiments with different Manures [fertilizers] on Permanent Meadow Land in 1859.

Different species growing on plots at the Park Grass experiment in 2006 as a result of different fertilizer and liming treatments; the plot in the foreground has received ammonium sulfate applications since 1856. Clover does not grow in this plot, but grasses do.

At Park Grass, the differential fertilizer treatments were applied to the meadow for the first time in 1856. The experiment continues to this day The purpose at the start was to evaluate the effect of fertilizer treatments on hay yield and nutritive value of the hay. But what they noticed, almost immediately, was something unexpected (very similar to that "crazy" disappearance of clover at Pender Harbour). Remember, this is what they noticed immediately, at the very start of the experiment:

Perhaps the most remarkable and interesting of the effects of the different descriptions [types] of manure [fertilizer], upon the complex herbage of which the experimental meadow was composed, was the very varying degree in which they respectively developed the different kinds of plants ... the experimental ground looked almost as much as if it were devoted to trials with different seeds as with different manures [fertilizers].

In the second year of the experiment, 1857, and again in 1858, the proportion of different plant species were measured in the different plots immediately after cutting the field. They reported the 1858 results as I quote below – note that I have changed the word manure to fertilizer for clarity in modern usage.

Perennial red clover [Trifolium pratense] amounted to little more than 1 per cent. of the total produce on the unfertilized land, but to nearly 18 per cent. of that grown by mineral fertilizers alone. Not any of it was found in the produce by either ammoniacal salts alone, or ammoniacal salts in conjunction with mineral fertilizers. There was little more than 1½ per cent. of it in the produce by farmyard manure alone, and less than ½ per cent. in that by farmyard manure and ammoniacal salts.

That is, in the second year of the experiment, there was 18 times more clover where mineral fertilizers were supplied in the absence of nitrogen. Adding ammonium sulfate, or ammonium sulfate with other minerals, eliminated the clover.

At the same rate of N, but applied in the nitrate form, and with P, K, and Mg added as well, many "weeds" including clover grow along with the grasses.

The implications of this for turf managers are pretty obvious. Fertilizer applications have an effect on what grasses and weeds will grow. Judicious selection of fertilizer can help to reduce weed populations. Herbicide use can be reduced or eliminated in some situations by adjusting the fertilizer applications. For more on this, see:

## Park Grass experiment video

##### 16 July 2014

Last week I was browsing the Sir John Bennet Lawes timeline and discovered this excellent video with plant ecologist Jonathan Storkey introducing the Park Grass Experiment.

The Park Grass experiment at Rothamsted was started in 1856 and has been continuously monitored ever since. That makes it the oldest experiment on permanent grassland in the world

The experiment was designed to investigate the effects of fertilizer application on hay yields. But what was quickly seen, within the first years of the experiment, was that application of the different fertilizers caused different species to grow. Lawes and Gilbert, in their first report on the experiment, remarked that:

The plots had each so distinctive a character in regard to the prevalence of different plants that the experimental ground looked almost as much as if it were devoted to trials with different seeds as with different manures [fertilizers].

C.V. Piper wrote in 1924, after a visit to Rothamsted, that the Park Grass experiment results "carry lessons of high importance in the growing of golf turf." These lessons extend to any kind of turf, including lawns. I wrote about this with Frank Rossi in The Park Grass Experiment and the Fight Against Dogma. The fertilizers that you apply will influence the species that grow, and the Park Grass experiment is the archetype of this effect.

The types and rates of fertilizer and lime applied to the Park Grass experiment result in dramatic differences in species composition and plot appearance

## An unfortunately underused and usually unappreciated grass

##### 15 July 2014

What is this underused and unappreciated grass? It is tropical carpetgrass (Axonopus compressus), the species that C.V. Piper, the first chairman of the USGA Green Section, wrote about as "the best of all grasses in the South for fairways." Piper added that:

It makes a dense, uniform turf even on pure sands and the leaves are stiff enough so that the ball is always well off the ground. The only other grass to compete with it is Bermuda; but under conditions where both will grow, carpetgrass makes far superior turf.

Tropical carpetgrass is the climax species as a managed turf in humid tropical climates. But it is barely mentioned in turfgrass textbooks, probably because the authors have focused primarily on the grasses in common use in the United States.

This is unfortunate, because tropical carpetgrass has a number of advantages as a turfgrass compared to species such as bermudagrass (Cynodon) or seashore paspalum (Paspalum vaginatum) that are sometimes planted in tropical environments. For example, it is possible to maintain tropical carpetgrass with no supplemental fertilizer, no irrigation, and no pesticides. In fact, that would be standard maintenance for tropical carpetgrass in many places – mowing, and not much else.

With these advantages compared to other grasses, it is encouraging to see two recent papers that have investigated some characteristics and performance of tropical carpetgrass.

Springer et al. compared bermudagrass, zoysiagrass, and tropical carpetgrass (they use the name savannahgrass for Axonopus compressus) at the University of the West Indies. They measured how much these grasses grew, and what quality they produced, when subjected to drought stress, waterlogging, and soil compaction. This was done in soil and in soil profiles with a surface sand layer to simulate the effects of sand topdressing.

Tropical carpetgrass through the green on the East Course at Wack Wack Golf and Country Club in Manila, Philippines

The full paper, Comparative Evaluation of Common Savannahgrass on a Range of Soils Subjected to Different Stresses I: Productivity and Quality, shows that tropical carpetgrass (savannahgrass) generally performed better in the growing environment of Trinidad than did the bermudagrass or the zoysiagrass. Averaged across all the stress treatments, tropical carpetgrass had the greatest clipping yield and the highest chlorophyll index. Zoysiagrass had the highest visual quality averaged across all stress treatments, with carpetgrass just behind, and then bermudagrass having the lowest visual quality.

Springer et al. concluded that tropical carpetgrass "showed a higher level of tolerance to applied stresses and warrants greater attention as a potential turfgrass under tropical conditions."

Tropical carpetgrass provides a full turf cover in heavy tree and structural shade at Bali, Indonesia

In Nigeria, Oyedeji et al. investigated tropical carpetgrass and other local grasses. Their paper, Performance of Some Local Nigerian Turfgrasses in Sole and Mixed Stands, shows data that again make a strong case for tropical carpetgrass as a turf in that climate. Compared to other grasses, tropical carpetgrass performed well, especially in the recovery after 2 weeks of daily trampling with soccer boots.

Unirrigated carpetgrass during the dry season at Hua Hin, Thailand

In a tropical climate, it is hard to find a grass that outperforms tropical carpetgrass. One of its advantages as a turfgrass is its adaptability to a range of mowing heights. Tropical carpetgrass can be maintained with almost no inputs, except for mowing, and in addition to that, it can be mown at heights from 3 mm to more than 100 mm.

A patch of tropical carpetgrass on a manilagrass green maintained at 4 mm in Chumpon, Thailand

## Helicopter spraying

##### 14 July 2014

Pine wilt can kill infected trees within a few weeks. The pine wood nematode does the damage, but it is the pine sawyer beetle that spreads the deadly nematode.

Thus, disease measures for pine wilt involve control of the pine sawyer beetle. I learned about this today at Keya Golf Club in Fukuoka. There are approximately 25,000 pine trees at Keya, and helicopter application of insecticide can be completed on all these trees within one hour. 400 L of spray solution are added to the tank, the helicopter sprays that out, and then the process is repeated 3 more times. In total, the helicopter will make 4 runs, each time with 400 L of spray solution.

After observing the spraying from the ground, I got to take a ride in the helicopter and enjoyed a fine view of this classic golf course.