If you work with warm-season grasses, you will want to have a look at this new paper by Reasor et al. on the variability of hybrid bermudagrasses used on putting greens.

Ever see anything like this? Off-types growing in a green? Wondered if the off-types are contamination by a completely different grass, or if the grass has mutated?

This paper explains what can happen, what has happened, and why. Plus it has a historical review of these hybrid bermudagrasses used on greens. Find out where they came from and how the grasses are related.

Sometimes I write about papers that are behind a paywall and most people can't read (or at least don't want to pay the high fees to purchase). I'm glad there won't be that problem with this article, as Reasor et al. have published this open access so everyone can read it.

I've just spent a couple weeks with the lead author Eric Reasor (pictured at right in Japan) collecting data from bermudagrass putting greens in Asia.

He's been doing a lot of interesting research about ultradwarf bermudagrass, off-types within those grasses, and the management of putting greens to minimize problems with off-types. Watch out for more interesting research from him on this topic.

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

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.

Of the many interesting things in the report by Gelernter et al. on the GCSAA's second nutrient use survey, I was especially intrigued by the part about soil testing.

First, a little background. If one has no idea how much of any mineral element is in the soil, then the logical amount to apply as fertilizer is just a little bit more than the grass can use. This guarantees that the grass will be supplied with all of each element that it can use. That's like an estimate of the maximum amount of fertilizer to apply.

Why soil test? Because soil testing allows for more efficient application of fertilizer. After finding out how much is in the soil, one can often reduce the quantity of fertilizer applied, because one knows that the soil can supply some portion of the plant's requirements.

With no soil testing, it makes sense to apply all that the grass could use. With soil testing, it makes sense to apply only the amount that the grass could use that can't be supplied by the soil. It's evident that the maximum amount of fertilizer should be applied when one doesn't know the nutrient content of the soil, and that in the most infertile soils, the quantity of nutrients required as fertilizer will be close to the maximum, with the quanity required as fertilizer decreasing as soon as the soils have some quantity of nutrients.

In the last chapter of A Short Grammar of Greenkeeping, I wrote that "I'd recommend soil testing, because in most soils the correct interpretation of soil tests can reduce the quantity of fertilizer that is applied."

You may have heard me say that soil testing is broken. For more background:

• Conventional nutrient guidelines: explaining what I mean by broken
• Why is the grass so good, but the soil test results so bad?

Now back to the GCSAA nutrient use survey results. Here's what the survey says:

"Despite the fact that respondents said that they used soil tests to reduce reliance on fertilizers, higher use rates were observed for respondents who conducted soil tests (Table 7). This apparent contradiction may be due to some of the turf fertility guidelines currently in use, which target higher nutrient levels than are required for acceptable turf growth ...

As a result, those who conduct soil tests with the belief that it will help them to reduce fertilizer inputs may end up unintentionally increasing fertilizer instead, likely because the guidelines used to evaluate their results may be higher than necessary."

That's not the way it is supposed to work. For more, check out the fertilizer and soil categories on the blog.

I look forward to some photos from Doug Soldat. For the past three years, he's had some fascinating photos to share of snow mold on creeping bentgrass. And each year, there was more snow mold where potassium fertilizer was applied, and less snow mold where potassium wasn't applied.

Spring of 2014

In the spring of 2014, there was more snow mold where K was applied.

Snow mold post was pretty popular today, so here's a combined pic. Numbers are lbs K2O/M/yr. pic.twitter.com/rTVG0jOrzd

— Doug Soldat (@djsoldat) April 2, 2014

Spring of 2015

Last year, there was also more snow mold where K was applied.

Pink snow mold on 'A4' bent sand green in WI. No K for 4 yrs on right, 0.2 lbs K/1000 every 2 wks for 4 yrs on left. pic.twitter.com/VSMlhcUmnv

— Doug Soldat (@djsoldat) March 21, 2015

Spring of 2016

This year, it happened again. There was more snow mold where K was applied.

No K on left, 0.1 lbs/1000 every other week on right. pic.twitter.com/9LoYCWcuHS

— Doug Soldat (@djsoldat) March 23, 2016

Doug will be talking about K in a TurfNet webinar in April: Is Your Potassium Program Hurting or Helping Your Turf?

On those creeping bentgrass plots in Wisconsin, adding K increases snow mold. No K had less snow mold.

At Rutgers, annual bluegrass plots deficient in K have had more anthracnose in summer and more winter injury. Eliminating the deficiency reduced those problems.

Then there is the MLSN guideline for K of 37 ppm. I recommend keeping the soil K above 37 ppm (Mehlich 3 extractant).

And there are hundreds of other studies about K. Some show a benefit from adding K, and some don't. I haven't read all of them, but I have read a lot of them. This sounds like it could be pretty complicated.

Actually, I don't think it is. Here's what seems to be the case, for both warm-season and cool-season grasses:

Ensuring the grass is supplied with all the K it can use will provide all the benefits associated with K. Adding more than that usually has no effect, other than wasting time and money, but sometimes has a negative effect.

As a turfgrass manager, all one has to do is ensure the grass is supplied with all the K it can use. This can be accomplished in 2 ways. One is by keeping the soil K above the MLSN guideline. A second is by applying N:K in a 2:1 ratio for cool-season grasses, a 1:1 ratio for seashore paspalum, and a 3:2 ratio for other warm-season grasses. I wrote about that in the final chapter of A Short Grammar of Greenkeeping and in The (New) Fundamentals of Turfgrass Nutrition.

Note that I do not recommend tissue testing for K (or any other element).

If you want to read more about K specifically, and about how the benefits of K come from correcting a deficiency, I recommend:

• Does potassium fertilizer really increase roots?
• Turfgrass nutrient guidelines, peer review, and potassium

When I saw there was a new article at Golfdom about sodium causing agronomic challenges on sand putting greens, I clicked the link to see what this was about.

Sodium causes agronomic challenges for sand putting greens See why & get recommendations. https://t.co/agWp0OHbXH pic.twitter.com/wRvd9HibIb

— Golfdom (@Golfdom) November 25, 2015

That link took me to the article by Obear and Soldat in which they explain that sodium does not cause agronomic challenges in sand putting green soils:

"Sand putting green soils have low clay contents and are therefore unaffected by sodium ... The findings from this study suggest that sodium will not negatively affect putting green soils with low clay content, including those constructed to USGA recommendations ... In the case of sand-based putting green root zones, which often have very low clay content, increasing exchangeable sodium percentage well above the standard sodicity threshold of 15 percent had no effect on hydraulic conductivity."

But the link is www.golfdom.com/sodium-causes-agronomic-challenges-for-sand-putting-greens, which seems the opposite of what the article is about. Sodium causes agronomic challenges for sand putting greens? Maybe if the sand putting green is made of clay.

That reminds me of the subtitle for the article Frank Rossi and I wrote about the Park Grass experiment for the Green Section Record. One of the things I thought was amazing was how soon the botanical composition on the Park Grass field changed in response to fertilizer treatments. We wrote about that in the article, quoting Lawes and Gilbert from their first paper on the botanical composition of the experiment, published just a few years after the first treatments were applied:

"the plots had each so distinctive a character in regard to the prevalence of different plants that the experimental ground looked almost as much as if it were devoted to trials with different seeds as with different manures [fertilizers]."

The fertilizer treatments began in 1856. We didn't put these quotes in the article, but it is clear the effects were noticed immediately. More from Lawes and Gilbert:

"So striking and characteristic, indeed, were the effects produced in this respect, that, in 1857 and 1858, the subject was thought of sufficient interest to induce us to request the examination of the plots by Professor Henfrey, to which he kindly assisted.

An endeavour was also made in the second year, 1857, to separate, and determine, the proportion of the different plants in carefully averaged and weighed samples, taken from the several plots as soon as the grass was cut."

So I was surprised that the subtitle of our article, when I saw it published, was Sometimes the value of a turfgrass management practice takes a long time to become apparent. That's not quite what we were trying to say.

The end of August marked 2 years of the Global Soil Survey. This report gives a summary of the results so far, shows a map of the locations -- now up to 9 countries! -- from which samples have been submitted, and announces that the survey will end on 31 December.

Thanks to all who have participated in this project for contributing samples from good performing turf at their sites. We now have a dataset which can be used for comparative analyses and as a reference for soil chemical conditions of professionally managed turfgrass.

A few related links:

• This year's report in PDF format
• If you would like to join the survey, a kit can be purchased here.
• This GitHub repository has all the files used to generate the report.
• The data are here.
• Last year's report has more details about our analyses of the data.

One doesn't need to apply supplementary potassium (K) after a rain, as I wrote in part 1 of this series, because such applications will invariably lead to application of way more K than the grass can use. In part 2, I showed a calculator that makes an estimate of how much K is reasonable to apply as fertilizer, based on how much K the grass will use.

Looking at this with soil test data, these four charts show what happens to K in the soil over time.

In 2002, I applied nitrogen (N) and K every two weeks to L-93 creeping bentgrass maintained as a putting green in Ithaca, New York. I collected soil samples every eight weeks. This summarizes what happened during the summer of 2002.

At the start of the experiment, before applying any N or K, the Mehlich 3 K was 86 ppm, and the water extractable K was 8.3 ppm. I've added a horizontal line at each of those levels, to indicate what the starting level of soil K was in this experiment.

Then the treatments started, N and K every 14 days. When no K was applied, what happened? The soil K went down. That is to be expected, because the grass uses K, so when the grass is growing one expects the soil K to go down if no K fertilizer is added.

What happened when a moderate amount of K was added? Over these 16 weeks in the summer of 2002, I applied 12 g N m^-2, and the K rate supplying 13 g K m^-2 in that time is close to a 1:1 ratio. From June to July, the soil K went up at that rate, because that is slightly more K added as fertilizer than the grass can use. Then from July to September, the soil K in plots supplied with the 1:1 ratio went right back to where they started the summer. The reason for the decrease is discussed below.

What happens when the K applied is way more than the grass can use? The highest rate in the experiment supplied 50 g K m^-2 over this time period, roughly a 1:4 ratio of N to K. And the soil test levels went up, because when one supplies a lot more K than the grass can use, that's what happens.

Why was the soil K higher in late July than in September? That is because the irrigation of this area was increased in August, and the rain + irrigation from the end of July to the time the samples were collected in September was double the evapotranspiration (ET).  From the start of the experiment until the samples were collected in late July, the rain + irrigation was just slightly higher than the ET.

The grass performance was good in all the plots, and equally good no matter if no K was applied, if a moderate rate of K was applied, or if the highest rate of K was applied.

There were six rain events with > 25 mm (> 1 inch) of rain during these 16 weeks. Adding K after rain would have accomplished nothing, other than supplying even more K than the grass would use, and supplying K that would mostly be leached out sometime in the future. By supplying the amount of K the grass uses, one can maintain a pretty stable level of soil K. Of course if the soil K is well above the MLSN guideline, then no K is needed at all, because the grass can get all the K it needs from the soil.

For more details about the experiment, see this paper from Soil Science.

When I watched the Golf Club Atlas interviews with Don Mahaffey last year, I was struck by the comments Don made about the health benefits of golf. Watch them here, starting at the 14:50 mark:

Don mentions things that are known to be good for health -- walking, spending time with other people, spending time in nature, solving puzzles.

That, he says, describes playing 9 holes of golf, but "no one is talking about that sort of thing, about the health benefits of golf ... I've never heard it packaged like that, anywhere, and I think there's opportunity there to change the image of pesticide, chemical, too much water and all of these things that we get branded with. And we talk about sustainability and we're using too much water and all of these things, but golf is good for you."

He's right, and after hearing his comments, I've been more attentive to articles on this subject. Here's a list I've enjoyed reading:

• From the NY Times, How walking in nature changes the brain
• From Landscape and Urban Planning, The benefits of nature experience: Improved affect and cognition
• From PNAS, Nature experience reduces rumination and subgenual prefontal cortex activation
• From Scandinavian Journal of Medicine & Science in Sports, Golf: a game of life and death -- reduced mortality in Swedish golf players
• From STERF, Societal benefits of golf -- Inspiration and ideas for local partnership

Bill Kreuser spoke with Kyle Brown about plant growth regulator applications on putting greens. Bill says "PGRs are pretty great because we can use them to do a lot of different things on our golf course." Listen to the full show here.