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May 2015

Morning and afternoon shade with PPFD capped at 1000

I've made some more calculations of morning and afternoon shade effects, this time with the maximum PPFD capped at 1000 μmol m-2 s-1. That is, if the full sun PPFD were more than 1000 at the time, I have set it to 1000. I've posted the full analysis here.

I downloaded hourly temperature data for seven locations, then estimated the PPFD and what the relative effects of morning and afternoon shade would be, during the hours when the temperature was close to an optimum for photosynthesis.

Here's a look at temperatures for a few locations.




And this is a summary of what these calculations predict.


The full report has a lot more data and details, including a monthly breakdown of estimated PAR in sun and in AM and PM shade. Thanks to @insaneturf for suggesting this.

Visits to this site by day of the week

Daily_virid_visitsI've been writing many of the posts on this site in advance, and scheduling them to post at a later date. I would like as many people to see these as possible. So which days, recently, get the most visitors? In the chart above, I show a boxplot for each day of the week, with the y-axis showing the total daily visits to the site from 1 January 2014 to 2 May 2015.

These are days as they are in Bangkok -- a visit from New York at 17:00 on a Sunday registers as Monday -- and the range for any day is wide, from a minimum of about 25 visits to a maximum of more than 300. Monday gets the most, then Tuesday, then Thursday, then Wednesday. The days with the fewest visits are Friday, then Saturday, then Sunday. I'm going to adjust the schedule for new posts based on these data.

Morning vs. Afternoon Shade for Cool Season Grass

Some months ago, we discussed morning sun and its importance for cool season grass.

I mentioned that I have a hypothesis about timing of light, one that goes something like this:

The most important time for full sunlight to reach a turfgrass surface corresponds to the optimum temperatures for photosynthesis for that species. More specifically, the longer the duration of time at which the PPFD on the turf surface is near the maximum the grass can use, while at the same time the air temperature is close to an optimum for photosynthesis, will optimize turf performance.

For cool season (C3) grass, I expect morning sun to be relatively more important than afternoon sun, because the temperatures in the morning will tend to be more suitable for photosynthesis than afternoon temperatures when it may be too hot. Note that this will vary based on where one is located. If the high temperatures in the afternoon are just right for C3 growth, then for that location I predict afternoon sun would be more important than morning sun.

To test this hypothesis, I downloaded the temperatures and sunshine hours for Mobara, Japan, in 10 minute increments from 1 January 2014 to 31 December 2014. Then I calculated the temperature-based growth potential (GP) for each 10 minute increment of the year, and I used the Ångström equation to calculate the PPFD. Then I selected only those increments during which the GP was greater than or equal to (>=) 0.5 and the PPFD was >= 0.5 of the the maximum potential PPFD for that time. Those times are shown in this chart, representing 62,870 total minutes during 2014.

You'll notice that there are not many times in the winter with low PPFD on this chart. that is because the temperatures at Mobara on winter mornings would tend to be too cold for GP to be above 0.5, so the times with warm enough temperatures to have GP above 0.5 will correspond with times of the day when PPFD is relatively high.

You can also notice that in July and August, there are not many times shown with a high PPFD. That is because it is so hot at Mobara in those months that the afternoon times, with a high PPFD, will have a GP below 0.5, and thus those 10 minute increments are not shown.

To simulate morning shade, I then reduced the PPFD by 80% for all times before 10 a.m. That reduces the amount of time with both GP and PPFD above 0.5 of their potential by 33%, from 62,870 minutes to 42,220 minutes. The simulated morning shade before 10 a.m. is shown in this chart.

One loses all the summer morning points, because by the time the shade is gone at 10 a.m. in Mobara, the temperatures are so hot that the C3 GP is less than 0.5.

Afternoon shade is not desirable either, but it is better than morning shade if there is a climate like Mobara. With simulated afternoon shade reducing PPFD by 80% for all times after 14:00, there is a 19% reduction in hours meeting the GP & PPFD cutoffs of 0.5 or more of potential. Compared to no artificial shade, the morning shade before 10:00 reduced the time for optimum growth by 33%, and the afternoon shade reduced the time for optimum growth bv 19%. This chart shows the afternoon shade.

Soil test summaries in Kentucky

Selection_091The University of Kentucky Cooperative Extension Service puts out some great material. You'll be familiar with the popular guide to control of turfgrass diseases. More recently, I read Fertilizing Your Lawn by Gregg Munshaw.

It's an excellent guide, and one I hope will feature an updated spelling of phosphorus in the next edition.

As I read, this passage caught my attention:

Recent summaries of Kentucky soil test results have revealed that more than 50 percent of homeowner turf soil samples test high or above for phosphorus and potassium. If the soil test results reveal that phosphorus and potassium are adequate, there is no need to apply more of these nutrients.

I'm always interested in summaries of soil test results, so I searched for those data, and found these summaries.  The median pH of the 8,299 lawn samples analyzed in the 3 year period of 2005 to 2007 was 6.4. The data are given in lbs/acre, and I divided by 2 to get ppm. These are the median values from the Mehlich 3 extractant.

elementmedian value (ppm)
K 157
P 36
Ca 1935
Mg 219
Zn 2.7

The University of Kentucky have their own recommendations and they seem quite reasonable. From 0 to 1 lb K2O and P2O5 will be recommended when the soil test K is 100 to 150 ppm and when the soil test P is 15 to 30 ppm, respectively. If the soil test K is more than 150 ppm, no K is recommended. If the soil test P is more than 30 ppm, no P will be recommended.

Can you imagine?

At Real Club de Golf El Prat, host of this week's Spanish Open, 3,600 trees fell in a violent windstorm on 9 December. The club has shared this video that shows the scale of the damage, and the impressive work that was done in the aftermath of the storm.

RCGEP Viento diciembre from Real Club de Golf El Prat on Vimeo.

That the playing surfaces are in such fine condition this week, after having to deal with the storm damage and all the disruption that caused, shows the skill and effort of the greenkeeping staff at the club.

View from the 10th tee

At the 1st tee, 6 months after the storm that felled 3,600 trees

Creeping bentgrass on the 1st fairway at Real Club de Golf El Prat

Relative effect of shade in Hamburg

As a continuation of these calculations I made about light, temperature, and shade influence on growth in Mobara, I have made another round of calculations for Hamburg.

I've used 2014 weather data for both locations. For Mobara, the data are more precise, because I used 10 minute intervals of temperature through the year, and I accounted for the reduction of clouds on PPFD based on minute by minute measurements of bright sunshine, collected into 10 minute intervals for a year. For Hamburg, I used hourly temperature data, and I did not attempt to account for the cloud cover, so the results shown here are as if every day were sunny with no clouds.

The summary of the data from Mobara showed that afternoon shade, starting 2 hours after solar noon, will reduce PPFD when temperatures are good for C3 grass growth more than morning shade during the months of October to April. Morning shade, from sunrise until 2 hours before solar noon, would be worse than afternoon shade from May to September.

How about in Hamburg?

First, I calculated the estimated average PPFD for every second at each hour of every day. This is 15 May 2014, as an example.


Then for every hour between sunrise and sunset, I calculated the GP for C3 grasses based on the hourly temperature. That gives this result, which is the GP on an hourly basis throughout the year.


Most of the hours in which GP is above 0.5 are from March to October. That makes sense, because the cold winter temperatures in Hamburg are not very good for grass to grow.

Then, I chose 0.5 GP as a cutoff for what I would consider good growing conditions for C3 grass, and I plotted the hourly average PPFD, for a sunny day with no clouds, for each of those hours with a GP greater than or equal to 0.5. In total, this comes to 2,279 hours in the year.


Finally, I simulated morning or afternoon shade by reducing PPFD by 80% from sunrise to 2 hours before solar noon (morning shade) or from 2 hours after solar noon until sunset (afternoon shade). The result is similar to Mobara.


Of course, full sun, with no shade, is best. Any type of shade is going to reduce the photosynthetically active radiation (PAR). But by making the calculations for every hour of the year, based on the temperature during that hour, one can predict the relative effect of afternoon or morning shade. In July, August, and September, morning shade at Hamburg should be more detrimental to the grass than afternoon shade. In the autumn it doesn't matter. Both shade timings are equally detrimental. In December, January, and February, it is so cold that there isn't any useful PAR at temperatures when the grass can grow well. And in March and April, afternoon shade is more detrimental than morning shade.

Another availability question: P & K & MLSN

In this presentation, I explained how one can determine turfgrass nutrient requirements by estimating turf nutrient use and comparing that to the amount of the nutrient in the soil.

One of the questions during the presentation involved nutrient availability, specifically of P and K. To paraphrase, the question was "How can one know that the P and K measured by the soil test, and compared to the MLSN guideline, are available to the grass?"

One can know the availability by doing a soil test because that is what a soil test is. A soil test is measuring the availability index of an element. When there is a lower amount of an element, there is less of it available to the grass, and when there is a higher amount of an element, there is more of it available. The MLSN guidelines are set at a level that we are confident is more than enough availability to produce good turfgrass.