This is what afternoon shade looks like

The photosynthetically active radiation (PAR) varies by time of day, season, and the presence -- or absence -- of clouds. If shade is imposed, the PAR is reduced for the duration of the shaded period.

This is what afternoon shade looks like, when shade that blocks 80% of PAR is imposed from 2 hours after solar noon until sunset.

PPFD by time of day in 2014 at Corvallis when shade blocking 80% of PAR is imposed from 2 h after solar noon until sunset

For more about PAR and shade, see these posts:


This is what morning shade looks like

The PPFD (photosynthetic photon flux density) every 5 minutes for a day, week, month, and year at Corvallis looks like this. I'm not so interested in the PPFD when the temperatures are too cold or too hot for photosynthesis. I selected only those times in 2014 when the C3 growth potential (GP) was greater than or equal to 0.5 (on a scale of 0 to 1), and the PPFD by time of day looks like this:

PPFD in 2014 when GP >= 0.5

What happens when there is shade in the morning that blocks 80% of the PPFD, from sunrise until 2 hours before solar noon? What does the PPFD by time of day look like then?

PPFD in 2014 when GP >= 0.5 and 80% shade is imposed until 2 h before solar noon


Course maintenance photos from the U.S. Open at Chambers Bay

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David Phipps, Northwest regional representative for the GCSAA, took photos of the course maintenance activities during the U.S. Open.

If you are interested in seeing photos of the people, place, and greenkeeping work, the more than 1000 photos taken by Phipps tell the story of the week.

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To see all the photos, view the Chambers Bay Agronomy 2015 album on Flickr. The photos shown here are examples of what you will find.

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This is what PAR looks like

I downloaded NOAA quality-controlled data for Corvallis on 5 minute intervals. An analysis of these data, and a comparison to Ithaca, are in this report.

These charts show the photosynthetically active radiation (PAR) by time of day, using the 2014 data.

This is the photosynthetic photon flux density (PPFD) every 5 minutes on 13 June 2014.

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It was cloudy for most of 13 June, with only a few of the 5 minute intervals having maximum potential PAR.

On a sunny day, like 10 August 2014, shown here, the PPFD increases from sunrise until a peak at solar noon, then decreases until sunset.

10 August 2014 PPFD at Corvallis

In these charts, the times shown are standard time, and the morning and afternoon separation is made based on the time being before (morning) or after (afternoon) solar noon.

That same week that contains 13 June is the 24th week of 2014, and all the measurements from that week are shown in the next chart.

PPFD for a week in June

For the entire month of June, the PPFD looks like this.

PPFD for June 2014

Then for an entire year, the PAR looks like this.

PPFD at Corvallis in 2014


On multifunctional golf facilities, the environment, and health

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I attended a seminar in Garðabær by golf course architect Edwin Roald about golf, Iceland, sustainable golf courses, land use, life expectancy, multifunctional golf courses, and much more.

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Roald is on the STERF (Scandanavian Turfgrass and Environment Research Foundation) board, and one of the main projects of STERF is the research and promotion of multifunctional golf facilities.

STERF have funded a number of projects about grass varieties, fertilizer, irrigation, plant growth regulators -- interesting as they are applicable to the Nordic region, but not so different from the topics studied elsewhere. What I find most interesting is the research into multifunctional golf facilities, and the business, societal, environmental, and health benefits of such. Read more about these projects here.

Don Mahaffey spoke in some ways about these topics in interviews with GCA (part 1, part 2) last year. I was reminded, in Roald's seminar, of the 40% mortality reduction measured in Sweden among golf players.

Interesting topics, and ones not always at the forefront in other parts of the world. For more images of golf in Iceland, many of which are multifunctional facilities, see this photo gallery. Below is a photo of the Geysir Golf Club, designed by Roald.

Geysir GC with erupting Strokkur

Two short articles on simplifying fertilization and soil test interpretation

I hope you will read both of these articles. They put put soil testing in context and explain an easy way to think about turf nutrition.

In 2008, I wrote this article for the Hawaii GCSA: Use the nutrients already in the soil -- simple fertilization. Here's an excerpt:

"If we look specifically at fertilization, I have a simple approach, yet it seems that many golf course superintendents doubt that my approach to fertilization can work at their facility. At most courses, I think this approach will work better than you might expect. Of the 14 essential mineral elements, nitrogen, phosphorus, and potassium are usually found in the highest concentrations in turfgrass leaves. We can test the soil to determine how much of each element is present in the soil and available for plant uptake. In most soils, even in sand rootzones such as USGA putting greens, there are adequate supplies of micronutrients and of elements such as calcium, magnesium, and phosphorus. This can all be confirmed by a soil test. Once there are adequate levels of a nutrient in the soil, adding more as fertilizer will have no affect on turfgrass performance.

The argument about what is adequate or not is one that we could have a day-long discussion about. Some fertilizer companies or soil testing services will set the target levels for nutrients in the soil to be much higher than what is required for good turfgrass growth. The base cation saturation theory is particularly notable for trying to “balance” elements in the soil, so even if there are adequate amounts of calcium and magnesium and potassium in the soil, there can still be recommendations to apply more of an element to try to “balance” the soil. This sounds good, but it costs money to purchase and apply unnecessary products.

I will list here, for golf course turfgrass conditions, what I consider to be minimum levels of adequacy for some of the essential elements ..."

You can download the article to read what those levels are. Or as an alternative, look at the MLSN guidelines.

The University of Nebraska-Lincoln Turfgrass Science Program recently released their guide to Simplifying Soil Test Interpretations for Turfgrass Professionals. Here's an excerpt from that article:

"While soil tests can be useful, their results are frequently over-analyzed and over-interpreted. 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."


Which affects growth more? Light or temperature?

I think temperature has more of an influence on turf growth, and I will use some data from Iceland to show why. This concerns the situation when there is not shade from buildings or trees, and looks at a situation when the light is more than sufficient for growth, but the grass does not grow.

I measured the photosynthetic photon flux density (PPFD), obtained temperature data, and observed turf conditions on some sunny days in Iceland.

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The turf was not growing and did not require mowing.

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There was a lot of photosynthetically active radiation (PAR).

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On sunny days, the PPFD was > 1000 µmol m-2 s-1 from about 09:30 to 17:30. That is 8 hours a day with PPFD at or above the light saturation point for C3 grasses.

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Each blue point is a single measurement of PPFD, and the red vertical line marks the mean time of solar noon on those dates

The light was pretty good, but the grass wasn't growing at all.

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On those sunny days, the daily light integral (DLI) was about 53 mol m-2 d-1.

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The evapotranspiration (ET) was about 1.5 mm d-1, and irrigation was being applied. But the grass only turned green where black sand had been applied. It wasn't growing.

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What is going on with irrigation being supplied and PAR reaching the turf in large amounts, but the grass not growing at all? The reason for that was the temperature, which was too cold for grass growth.

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There wasn't a single day in that two week period with a mean temperature reaching 5°C. In fact, the mean temperature over that period was 1.4°C.

The temperature based growth potential (GP) shows that the GP was close to 0 every day.

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Even though the light was close to an optimum, the temperatures were too cold for growth.

Excluding cases of shade from buildings, shade, or landscape features, I struggle to imagine the inverse of the situation described above. That is, when is there ever a situation in which the temperature is close to an optimum for growth, but the PAR is such that grass can't grow?

This controlling effect of temperature on the ability of grass to grow is one of the reasons I find the GP so useful.


What empirical formula do you use for determining CEC in sandy soils with no clay particles?

A correspondent wrote with that question about CEC (cation exchange capacity) calculations.

Sand is inert. It doesn't have structural negative charge, and even if it did, the surface area of sand is small. One can consider the CEC of sand to be nil.

But soil organic matter (OM) has a pH-dependent negative charge. One can estimate the CEC based on OM and soil pH. This equation is based on Contribution of organic matter and clay to soil cation-exchange capacity as affected by the pH of the saturating solution by Helling et al..

Express OM in units of g/kg. Then $OM(-311 + 268(pH)) = CEC$ with the CEC in units of mmolc/kg (millimoles of charge per kg of soil).

A sand with OM of 2% (20 g/kg) and a pH of 7 would have a CEC of 31 mmolc/kg. Keep the OM the same, but let the pH be 5.8, and the CEC will now be 25 mmolc/kg.

For more about this, see:


Turfgrass Mystery: the case of the greens with the greener grass

I'm changing the format of the #TurfMystery posts. Rather than ask for guesses, I'll just present the mystery and the answer together. I expect this will be just as interesting, and will avoid cluttered Twitter timelines.

Here's a mystery about green patterns in straight lines on greens in Iceland. This mystery is similar, at least in appearance, to these previous ones:

This is Iceland in early May. There was still snow on the mountains around Reykjavik.

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The greens in question are primarily fine fescue. I noticed straight lines where turf was greener in one section and less green in another.

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Was this caused by fertilizer?

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Or was it a different variety of fescue, with a darker green color? Or perhaps the remnants of a pigment application from the autumn?

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Maybe a nitrogen or iron application and only applied to a portion of the green?

The answer is not fertilizer, and not a greener variety of grass. What caused this was the application of dark topdressing sand.

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Topdressing in the spring with dark sand is a great way to smooth out the green surface after a long winter, and it makes a big difference in the color of the grass due to the slight increase in temperature.

The areas in green received more sand. The areas that were less green had less sand applied, or were skipped, due to irregularities in the distribution pattern from the topdresser.

You'll see the difference in color from a closer look at a skip.

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With such a short growing season, and cool temperatures, the practice of topdressing with black sand in the spring makes a lot of sense, and makes a big improvement in the turf. This is done on football pitches too.

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For more turfgrass mysteries, see the archive here.