Photosynthetically active radiation: this is what cool season grass may "see"

I've shared a series of charts (links at the bottom of this post) that show the photosynthetically active radiation (PAR) by time of day at Corvallis, Oregon. These charts are based on measurements made on 5 minute increments during 2014.

Those charts show the photosynthetic photo flux density (PPFD) on the y-axis and the time of day on the x-axis. At night, the PPFD is 0, and during the day, the PPFD is > 0, reaching a maximum of about 2000 μmol m-2 s-1 at midday during summer when there are no clouds blocking the sun.

However, cool-season (C3) grasses are considered to have a light saturation point of about 1000 μmol m-2 s-1. That is, the PAR from a PPFD up to about 1000 μmol m-2 s-1 can be used, and at that point the grass can't use any more light. So the PPFD that can be used by the grass may look something like this.

PPFD every 5 minutes in 2014 capped at 1000

When the measurements made every 5 minutes are filtered to include only those time increments in which the temperatures are reasonably suitable for photosynthesis -- that is, not too hot, and not too cold -- and then morning or afternoon shade are imposed, the charts look like this (morning shade, afternoon shade).

PPFD capped at 1000 with morning shade

PPFD capped at 1000 with afternoon shade

These posts show additional charts and calculations of total PAR over the course of a year:

Monthly Turfgrass Roundup: June 2015

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

These articles on turf nutrition.

Mike Richardson shared this photo of large patch on Zoysia matrella:

A large gallery of U.S. Open course maintenance photos by David Phipps.

Comparing photosynthetically active radiation (PAR) and temperature at Corvallis and Ithaca.

Black topdressing sand has a dramatic effect in spring.

Doug Soldat is finally seeing potassium (K) deficiency symptoms on bentgrass in a sand rootzone:

This formula gives an estimate of cation exchange capacity (CEC) in sand rootzones.

Jim Kerns reports on the TurfDiseases blog about pythium and leaf spot on bermudagrass.

Does light or temperature have a more prominent effect on turf growth?

Al Bancroft shows bentgrass nursery plug recovery:

Two short articles on simplifying soil test interpretation.

This is what photosynthetically active radiation (PAR) looks like by time of day.

This is what morning shade does to PAR.

This is what afternoon shade does to PAR.

Frank Rossi and Micah Woods spoke on TurfNet RADIO.

Check Out Science Podcasts at Blog Talk Radio with TurfNet RADIO on BlogTalkRadio with TurfNet RADIO on BlogTalkRadio

Multifunctional golf facilities.

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.

Managing salt by leaching

Selection_010My 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 (ECe) from exceeding a threshold value.

The article is available in both Chinese and 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?

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


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.


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.






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.


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

2015-04-29 11.15.55
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.


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."