I enjoyed reading the recent paper by Hodges et al. on Quantifying a daily light integral (DLI) for establishment of warm-season cultivars on putting greens. They measured the DLI at Starkville for the duration of this experiment, from 13 June to 29 September 2013 and again from 2 June to 27 September 2014. The mean DLI in full sun, on their test area, was 42.3 mol m^-2 d^-1 when averaged across those dates.

Last year I made some calculations to estimate DLI. You can read about that in Estimating daily light integral in 4 Tennessee cities. I wondered what that calculation method would give for a mean estimated DLI in Starkville. That is, Hodges et al. measured DLI with a quantum light sensor from Spectrum Technologies, and I wanted to check my calculations to see how close the estimated DLI was to the measurement.

The code for the calculations is in the dli_tn repository.

In full sun, Hodges et al. measured an average DLI of 42.3. The mean estimated DLI, using my calculations, for those same dates, was 40.6. Not too far off. To put the error of my estimate into context, that's a difference of 1.7 moles. An hour of midsummer midday sun at that location will have about 7.2 moles of PAR per hour, so 1.7 moles is equivalent to about 15 minutes of midsummer midday sun.

This 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.

After I wrote about no problem DLI levels, Brandon Horvath asked if I could get DLI for some cities in Tennessee.

For a description of how I made the calculations, see Estimating daily light integral (DLI) in 4 Tennessee cities. All the scripts are in this GitHub repository.

In previous posts, I looked at:

• when it is too hot to grow bentgrass
• a more detailed look at this, with better data
• long term temperature time series in Tokyo

In Tokyo, there is quite an increase in average annual temperatures since 1876. I'm expecting this has to do with an urban/concrete heat island effect. I downloaded data for Knoxville, Tennessee (data link and code for charts here) from 1910 to 2014 and plotted it. I wanted to look at three things. Trends in summer duration, trends in temperatures in the hottest month, and trends in overall temperatures.

Creeping bentgrass will not perform well when soil temperatures are high. When the nighttime low temperatures are above 21°C (70°F), we know the soil temperatures will be above that temperature too. I like to estimate the duration of summer that will put heat stress on creeping bentgrass by counting the number of days when the temperature remains above 21°C.

In Knoxville, a cool summer will have less than 20 days with a low above 21°C, and a hot summer will have 40 to 60 days above that temperature. Unlike Tokyo, there is no consistent trend in this summer duration at Knoxville, although it has been gradually increasing since about 1970.

The hottest month in Knoxville, on average since 1910, is July. I plotted the average daily high and low for July in each of the past 105 years. In the hottest month of the year, the temperatures (high and low) are staying pretty consistent.

 For the average annual temperatures in Knoxville, it is much the same.

Average lows are about 10°C and highs 20 or 21°C. Not a whole lot of change in 105 years. The average temperature in Knoxville for the past 105 years is 15.1°C. Tokyo used to be cooler than Knoxville, and now Tokyo is warmer than Knoxville.

Jim Brosnan and Eric Reasor from the Department of Plant Sciences at the University of Tennessee were on WVLT to talk about bermudagrass, crabgrass, white clover, and the Turf and Ornamental Field Day.

Last week I visited three sod farms near Memphis with Dr. Jim Brosnan from the University of Tennessee, where I am an adjunct professor in the Department of Plant Sciences. We saw grass production on a different scale to what I am used to seeing on golf courses and sports fields. The mowers are a lot bigger, and so are the sod cutters and all the other equipment used to plant, maintain, and harvest these huge fields of turf.

The grasses grown on these farms were different varieties of bermudagrass (Cynodon), japanese lawngrass (Zoysia japonica), manilagrass (Zoysia matrella), and tall fescue (Festuca arundinacea).

I got to meet Bobby Winstead of Winstead Turf Farms, current president of Turfgrass Producers International (TPI). His farm is growing some of the popular new varieties such as Celebration and Discovery bermudagrasses and Palisades and Royal zoysiagrasses. 

We also went to Battle Sod Farm in the Mississippi Delta and McCurdy Sod Farms in Dyer, Tennessee. We learned about irrigation and drainage of the huge sod fields, which are often watered by center pivot irrigation. We saw different types of verticutters and sprigging and plugging machines, all of which allow grass to be planted and grown and harvested at a scale I had never seen before.

Dr. Brosnan and I spoke at the monthly meeting of the Midsouth Turfgrass Council, where he introduced a new mobile weed manual and I explained how manilagrass sod is produced near Bangkok. In the United States, turfgrass production in general is very much mechanized, and the growth of manilagrass specifically is slow because of the temperate climate, with it taking more than a year to get a harvestable crop. At Thailand, the situation is almost completely reversed. Turfgrass production in general is almost entirely done manually, and manilagrass sod can be produced in five or six weeks, because it grows so well in the tropical climate.

I made this video a few years ago showing the techniques used in Thailand, and I will be putting together an updated version soon. Whether it is the large scale sod production in the United States or the small scale production in Thailand, it is fascinating to study about the techniques used to produce good turf.

Related articles

Turfgrass Mystery at the sod farm

Manilagrass Tees and Divot Problems, Fact or Fallacy?

Presentation Slides and Handouts from Thailand Conference Available for Download

An article in this month's Golf Course Management magazine focuses on my work with the Asian Turfgrass Center. 

As a longtime reader of this magazine and an 18 year member of GCSAA, it was fun to read this article about the work that I do. 

Read the article online here to learn about, among other things, why I decided to be a turfgrass scientist, how I came to work in Asia, what I'm working on now, how many miles I flew in the first half of 2012, what professional tour my dad played, at which university I am an adjunct professor, and what Dr. Frank Rossi, Nicer Landas, CGCS, Vu Minh Son, and Jin Hai Bo have to say about me and my work.

I visited Tennessee this month, speaking at the packed Tennessee Turfgrass Association conference, meeting with faculty in the Plant Sciences Department at the University of Tennessee (of which I am an adjunct faculty member), learning about some of the turfgrass research projects now underway at the University, and teaching this semester's first session of the Turfgrass Rootzone Construction and Management course.

I participated in a panel discussion with Rodney Lingle (Memphis CC), Matt Shaffer (Merion Golf Club), and Chris Hartwiger (USGA Green Section) in which we discussed ultradwarf bermudagrass management, preparation for the 2013 US Open, cold tolerance of bermudagrass, and heat tolerance of creeping bentgrass. I gave three other presentations at the conference, on topics ranging from course preparations for the Open Championship, fertilizer for sand rootzones, and turfgrass management in Asia. The attendance at the conference was superb. In fact, for many of the presentations it was standing room only, and the trade show was bigger than I had expected too.

At the University of Tennessee I saw the now completed Center for Athletic Field Safety with some really great looking synthetic surfaces along with natural turf. This impressive facility is being used for some cutting-edge research about sporting surfaces, biomechanics, and athlete safety.

I saw a lot of other research as well -- zoysia trials, lots of weed control work, many with the new herbicide indaziflam, rooting experiments, seedhead control of zoysia -- suffice it to say that there is a lot of interesting information being developed by the turfgrass team at the University of Tennessee.

We also discussed turfgrass educational programs in Asia and weed control in India for upcoming sessions of the Indian Golf Union's Greenkeeper Education Programme.

At the end of my week in Tennessee, I taught the Plant Science 442 course, Turfgrass Rootzone Construction and Management. I talked about sand rootzones, why we do core aerification (coring, hollow-tine aerification), and what some of the challenges are in managing turf in sand rootzones. I spoke, basically, about these topics:

• Managing the rootzone (handout from Sustainable Turfgrass Management in Asia 2010)
• Managing the rootzone (presentation slides from Sustainable Turfgrass Management in Asia 2010)
• Do fairways need a sandcap? (article from Asian Golf Business)

Last week at the Tennessee Turfgrass Association conference I gave a 30 minute presentation with the title Chemical Fertilizer Programs for Sand Based Rootzones. But this topic doesn't always require 30 minutes to explain - I like to distill this topic into the most important principles. There is plenty of experimental and empirical evidence to show that these four principles, if followed, will give excellent results.

1. Apply the right amount of nitrogen
2. Ensure soil pH is more than 5.5 and less than 8.3
3. Ensure soil potassium (as measured by the Mehlich 3 extractant) is kept above 35 ppm
4. Ensure soil phosphorus (as measured by the Mehlich 3 extractant) is kept above 18 ppm

The End (of the 1 minute version of this topic)

If you are especially interested in mineral nutrition for turfgrass or soil nutrient analysis for sand rootzones, you may want to read or watch some of these more lengthy expositions.

Simple Fertilization: Use the Nutrients Already in the Soil, from the Hawaii GCSA newsletter

Minimum Levels for Sustainable Nutrition (MLSN) with PACE Turf

PACE Turf Potassium Sufficiency Video, on Youtube

Soil Testing: It Does Not Have to be Difficult, on Youtube

Creating an Excellent Playing Surface: Managing the Plant, especially section 2 regarding nitrogen application

Does Potassium Fertilizer Really Increase Roots?, from TurfNet Monthly

And for those who really want to reduce P and K, consider the implications of The Park Grass Experiment and the Fight Against Dogma, written with Dr. Frank Rossi and published in the USGA Green Section Record

I visited the East Tennessee Ag Research and Education Center in Knoxville yesterday to see many of the turfgrass experiments now underway. This large facility has vast swaths of turfgrass plots sweeping down to the Tennessee River.

What really caught my eye, and is now under construction and nearly ready for planting, is an exciting new research center. The Center for Safer Athletic Fields is a partnership between Astroturf® and the University of Tennessee. Dr. Jim Brosnan explained how these 60 miniature athletic fields and other research plots at the Center have been designed for many interesting experiments. From the press release announcing this Center:

The unique outdoor research facility will comprise 60 small-scale athletic research fields constructed from a variety of playing surfaces. UT turfgrass scientists will compare the safety and performance of synthetic playing surfaces to natural grass surfaces. Field qualities will range from those employed for professional-level sports to surfaces used by schools, public parks and recreation fields. 

Some of the other research trials I saw included:

• Bluegrass evaluation plots
• Zoysiagrass variety evalution
• A multitude of weed control plots, including some really interesting pre-emergent product results, Poa annua control trials, and innovative combinations of herbicides with cultural practices to optimize weed control
• Seedhead and disease control trials
• Ultradwarf bermudagrass and seashore paspalum and zoysiagrass on putting greens

The UT Turfgrass Field Day will be held on September 15, 2011. I wish I could be there for that. Seeing the various grasses right at the end of summer, when we might expect warm-season grasses to be at their best, and cool-season grasses to be at their worst, would be an ideal time to see which grasses perform best and which maintenance practices and products perform well to create the desired playing surfaces.