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June 2016

Checking my calculations

Selection_072I 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.

Six turfgrass Shiny apps

These Shiny applications make calculations related to turfgrass management.

Evapotranspiration (ET) calculator

Returns the reference and crop evapotranspiration for a day given inputs of latitude, maximum and minimum air temperatures, and crop coefficient. Based on the Hargreaves equation.

Sustainability index

Returns the sustainability index (SI) based on soil test inputs. This is a direct comparison of input soil test results to the MLSN data.


PPFD by time, date, and location

Returns the expected photosynthetic photon flux density (PPFD) for a second within any specified minute, given inputs of latitude, longitude, date, and time. Also returns expected daily light integral (DLI) at that location if it is sunny all day.

MLSN K fertilizer calculator

Calculates the fertilizer K requirement given inputs of grass species, soil test K, and annual N rate.

ET(蒸発散値: 標準 ETと特定作物 ET)計算機

このプログラムは、標準蒸発散値(ETo) を、年月日、緯度、その日の最高気温と最低気温を基にしてmm 単位で計算します。算出された ETo に、作物係数を乗算すると、 その作物の蒸発散値(ETc)が求められます。これらの計算はHargreaves の ETo

MLSN ガイドラインからK要求量を求める

ここでの計算は、持続可能な最低栄養 (MLSNガイドライン) をベースとしています。

The MLSN guidelines, data, and reproducible research

Our preprint on the MLSN guidelines is now available. It was published today at PeerJ Preprints, as Minimum soil nutrient guidelines for turfgrass developed from Mehlich 3 soil test results. We wanted to share what we have done so far, make this paper available for citation in case anyone needs to cite something more technical than our 2014 GCM paper, and also solicit feedback about this paper before we submit it for peer review.

If you are interested in this, you probably care just about the article. Maybe just the abstract of the article. Maybe the abstract and a glance at the introduction and then a skip to the discussion and conclusions. That's fine. We'll be glad if you read any of it.

Beyond the article itself, I want to share what I'm most interested in with this project. That's the reproducibility of it. And the openness of it. We are sharing the results, and also the data and the code to generate the results and the code to generate the paper itself.



We  want to make sure that anyone who wants to read it can do so, so we share it as a preprint, and will make sure if a later version is published, that it is open access. You won't have to worry about clicking to read the article and hitting a paywall. I hit a couple paywalls this afternoon in my own research, and snapped these screenshots.



Those type of paywalls won't happen with this project.

Beyond that, however, the paper is reproducible*. That is, we are sharing all the data, all the code, and all the text; you can run the files and generate the exact same results -- in fact, the exact same pdf. You probably don't have all the software on your computer to do that, but you could. It is all open source and free. R, LaTeX, and some R libraries. We used knitr, VGAM, xtable, and dplyr in this project. You can check our files and see which libraries we used. You can check the code to see how we made the figures. How the values in the tables were calculated. You can see what functions we wrote to calculate the MLSN guidelines.

With this type of work, you can see what we did, and you can also see how we did it.

Furthermore, we've made the data, as we did with the Global Soil Survey data, freely available with no copyright. You want to study soil test results and have a need for more than 16,000 samples, or a subset of them? Have at it!

*reproducible research -- if you are interested in this, I suggest reading this post at Simply Statistics:

The Real Reason Reproducible Research is Important

High quality turfgrass is often produced in soils that don't have enough nutrients to produce high quality turfgrass.

That's the first sentence of our article about the development of the MLSN guidelines, published today as a preprint at PeerJ Preprints. You can read the article there and find out how (and why) we developed the guidelines.

We have also shared all the data used to develop the guidelines, and you can find the code used to calculate the guidelines in the 2016_mlsn_paper folder on GitHub.



99 article titles


I've been writing a monthly article for ゴルフ場セミナー (Golf Course Seminar) magazine since May 2008. That's 99 articles so far, and 118,518 words. The best of these will be published in English, sometime; for now they are only available in Japanese.

Starting in May 2008 (#1) and going up to July 2016 (#99), these are the article titles in English.

1. What is Greenkeeping? The 6 Basic Principles
2. Soil Water: How to Manage it in the Summer
3. Fertilizer for Grass: Soil, Leaves, and Growth Potential
4. 5 Maintenance Activities That May Increase Roots
5. Coring: Do it Right, and Get Better Greens
6. Simple is Better: An Amazing Experiment at Rothamsted
7. Sand Topdressing by Numbers
8. 2008 International Turfgrass Science Quiz
9. Why is Grass Green?
10. 2008 International Turfgrass Science Quiz - Answers & Discussion
11. Golf Course Maintenance Expenditures in 2009
12. Putting It All Together: summarizing the six points of greenkeeping
13. The most important thing to know about creeping bentgrass
14. The 2009 US Open, Bethpage Black, and Integrated Pest Management
15. Effective spraying: nozzles, water volume, and droplet size
16. The Critical Component of Putting Green Management
17. The Critical Moisture Content of Soils
18. Some New Turfgrass Research Results
19. The Optimum Level of Plant Nutrients in the Soil
20. A Christmas Gift List for the Turfgrass Scientist
21. Two Equations for the New Year
22. Old and New, from Scotland to China
23. Roll Three Times a Week for Better Greens
24. Turfgrass Maintenance by the Numbers
25. Current Trends in GC Maintenance
26. Thatch: Definition & Management
27. Does Phosphorus Cause Algae on Putting Greens?
28. Pebble Beach Putting Greens: Playing Condition vs. Appearance
29. One Good Thing About the Summer
30. The Foundation for a System of Golf Course Maintenance
31. Practical Application of Turfgrass Science Principles
32. Labor Analysis and Priority of Maintenance Work
33. A Scientific Guide to Turfgrass Maintenance this Year: Part 1
34. A Scientific Guide to Turfgrass Maintenance this Year: Part 2
35. A Scientific Guide to Turfgrass Maintenance this Year: Part 3
36. Data + Science + Technique = Better Grass Conditions
37. How Poor Greens Became Excellent Greens at Vietnam: a case study
38. Tublamu Navy Golf Course & the 2004 Indian Ocean Tsunami
39. Thai Country Club: Great greens with terrible water
40. An Almost Insurmountable Problem: nematodes
41. What’s in the irrigation water at the Home of Golf?
42. Converting to Ultradwarf Bermudagrass: why and how
43. Choosing Soil Moisture Meters
44. Using Soil Moisture Meters
45. Firm Putting Greens at Australia
46. Fertilizing Greens in the West Coast Style
47. Using Soil Test Data to Improve Turfgrass Conditions
48. A Common Cause for Putting Green Problems
49. Rolling Greens: What do the Data Show?
50. Green Speed and the Brede Equation
51. Cooling the Soil
52. Soil Moisture Content of Putting Greens in Japan
53. The Clegg Hammer and the “Hardness” of Putting Greens
54. Cooling the Soil at Night
55. Measuring Photosynthetically Active Radiation
56. Green Speed Variability
57. Green Hardness: Yamanaka Tester vs. Clegg Hammer
58. The Surface and Soil Temperatures of Putting Greens
59. The pH, N, P, and K of Putting Green Soils in 2012
60. The Ca, Mg, S, and Micronutrients of Putting Green Soils in 2012
61. Measuring the Reliability of Putting Greens
62. Putting Green Soil Moisture Content and Management in Summer
63. The Effect of Rolling on Green Speed and Green Hardness
64. Putting green surface temperatures and syringing
65. Fertilizer planning and nutrient mass balance
66. Green Speed Summary
67. Temperature-based growth potential: a study in 3 seasons
68. What is the effect of day length on turfgrass growth and nitrogen requirement?
69. Organic Matter Management in Putting Greens
70. When is the best time to core aerify putting greens?
71. A new way to look at turf nutrient requirements
72. A Method to Predict the Optimum Time for Overseeding
73. A counterintuitive approach to irrigation
74. An important note on the timing of growth regulator and nitrogen applications
75. Anthracnose and healthy greens in summer
76. New research about management of thatch and organic matter on putting greens
77. How many nutrient cations can a green hold?
78. Fertilizer, leaching, and cation exchange capacity
79. What do wetting agents really do?
80. Nitrogen fertilizer — when it is used by the grass?
81. Does nitrogen fertilizer increase or decrease roots?
82. Temperature, humidity, and combining them for summertime heat indices
83. Mowing and the 1/3 rule
84. Timing of nitrogen application to greens
85. Putting green performance tests: professional estimates
86. A new summary of putting green stimpmeter, surface hardness, and soil water measurements
87. Are summer nights getting hotter?
88. Fine fescue putting greens and tournament golf
89. Wind, tournament golf, and the 5 day Open Championship
90. Some useful things to understand about light
91. An analysis of three years of tournament green hardness data
92. An analysis of three years of tournament green speed data
93. What do P and K mean, exactly?
94. Two methods for precision water management
95. Course conditioning guidelines for PGA Tour tournaments
96. How much does water use vary from green to green?
97. The combination of temperature and sunshine to compare locations
98. What’s the irrigation water requirement?
99. Green speed, pace of play, and more green speed

Monthly Turfgrass Roundup: May 2016

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

An ET calculator for any location, now in a Japanese version.

From Andrew McDaniel, images of earthquake damage on Kumamoto golf courses:

From Bhupendra Singh, Tifdwarf roots, growth potential, and fertilizer.

Dave Wilber and Mike Young on the TurfNet Renovation Report.

Sharing slides. Why isn't this more common?

Megan Kennelly on spray nozzles and water quality.

Guide from the USGA Green Section on Turfgrass Fertilization.

How to save 82% on fertilizer cost.

Achim Dobermann with Park Grass videos.

Avoiding nutrient deficiencies from GCM China.

More from the air: view from the helicopter at Keya GC.

Shade and sun.

From Scott McElroy, is there an upper limit to how firm and fast a surface should be.

An interesting technique for introducing Cynodon to Agrostis fairways.

Alan Windham with images of pythium blight on ultradwarf:

A new Pace of Play Manual from the R&A.

Soil organic matter decreased with concurrent reductions in coring and topdressing; data to support the anecdote.


More data to support an anecdote; clipping amounts.


Water quality and pesticide performance.

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.