Ryan Goss made a good point in the discussion about how much fertilizer is applied on golf courses. Original blog post here.

@asianturfgrass maybe those that soil test are just more likely to fertilize in general?

— Ryan Goss (@NMSUTurfgrass) December 29, 2016

There are two basic scenarios.

The first scenario is no soil testing, in which it makes sense to apply the same amount of fertilizer, F, as the grass can use, G. One doesn't know how much is in the soil, one can assume the soil will supply nothing, and as an equation this can be represented as F = G. Maybe add just a little more to be sure. Call it F = G + 10%. I'd think of this as a hydroponic situation, where the soil can supply nothing.

The second scenario is with soil testing. In this case, the amount of fertilizer to apply should be the amount that the grass will use that cannot be supplied by the soil, S. Any amount that is supplied from the soil is not required as fertilizer. In this scenario using soil testing to find what the soil can supply, the amount to apply as fertilizer becomes F = G - S. Maybe add just a little more to be sure. Call it F = G - S + 10%. If the soil can supply nothing, then S is 0 and the equation simplifies to the "hydroponic" situation described in the first scenario.

With these simple equations, it is apparent that the amount of fertilizer to apply, represented as the value F, will always be lower in the second scenario, with soil testing.

Ryan is right that those who soil test are probably more likely to fertilize in general. But there is something interesting if we look at the data in Table 7 from Gelernter et al. (2016). Phosphorus and potassium are often recommended based on soil tests, but turfgrass nitrogen rates are not based on soil tests. Therefore, I'm going to use the amount of N applied as a baseline estimate of how much more likely soil testers are to fertilize than non-testers.

I use the log percentage (L%) to show the relative changes. More about log percentage at the end.

I took the average L% increase across all areas of the golf course for each nutrient. A typical 18 hole golf course that soil tests will have an 18 L% increase in nitrogen rate compared to a typical golf course that doesn't soil test. Because nitrogen is not based on soil tests, I'll pick that number and say that the overall increase in fertilizer from those who soil test is likely to be 18 L% more than those who don't soil test, just based on what Ryan pointed out.

Then I move to phosphorus and potassium and compare them to the 18 L%. Phosphorus and potassium recommendations are based on soil tests, so if they increase by about 18 L% too, then we can't say soil tests have anything to do with it. Phosphorus fertilizer (shown as P₂O₅) was variable. The average was a 19 L% increase when soil testing, but there was a wide uncertainty interval around that estimate.

Potassium had an average increase of 39 L%. Even if the typical golf course that soil tests is already likely to apply 18 L% more fertilizer in general, that baseline increase does not explain the 39 L% increase in potassium fertilizer.

Why log percentage (L%)? This is described in Törnqvist et al. (1985) as "the only symmetric, additive, and normed indicator of relative change."

I didn't want to compare the absolute amounts of N, P, and K applied, because it is normal that one will apply more N than K, and more K than P. Saying the soil testing sites used half a pound more N (it was 0.4875 lbs more, to be exact) than the sites that didn't soil test is fine. Then I can also say that the soil testing sites used 0.16 pounds more P₂O₅ than did the sites that didn't soil test. Both those statements are correct. But that's not exactly what I want to compare. I don't want the absolute difference. I can't compare the half pound of N to the 0.16 pound of P. What I'm interested in is the relative change.

I could use the usual percentage, but that has problems too. The sites that soil tested used 3 lbs of N on average. 3/2.5 = 1.2. 3 is 120% more than 2.5. A 20% increase. So is that also a 20% decrease? 20% of 3 is 0.6. That's not symmetric. And 2.5/3 = 0.833. So is it a 17% decrease then? Or a 17% increase? It is confusing.

The log percentage solves this. ln(3/2.5) = 0.182. An 18.2 L% increase. ln(2.5/3) = -0.182. An 18.2 L% decrease. Very convenient.

These ten posts from 2016 had the most pageviews. Here they are, counting down from the tenth to the most viewed post. And I'm including a pretty photo of Mt. Fuji just for fun.

[10] November, Both of these are worth your time about organic matter management, and coring greens, or not.

[9] May, Roots, growth potential, and fertilizer discussing what was applied to putting greens in New Delhi.

[8] April, Is this the most common oxymoron in turf? about a question that just won't go away. Can nutrients be adequate but not available?

[7] November, Fall potassium and winter traffic on a bentgrass green about the remarkable tolerance of creeping bentgrass to traffic when frozen.

[6] October, Daily versus monthly calculations of ET and irrigation requirement in which I show that a daily soil water balance gives a totally different irrigation requirement than does a monthly calculation using the standard method.

[5] February, Which products and technologies are truly beneficial and cost-effective? is a quote from Dr. Carrow's Green Section Record article on Purchasing new products and technologies: an ethical and common-sense approach. He explains why this is an ethical issue, and gives 7 questions to ask about products and technologies.

[4] January, Knowing which soil test results are important can simplify turf management. That's a quote from Bill Kreuser; he says that "while soil tests can be useful, their results are frequently overanalyzed and overinterpreted."

[3] September, Fast release fertilizer, fertilizer burn, and root growth in which those topics were mentioned.

[2] November, High expectations, about the energy use and greenhouse gas emissions from golf courses.

[1] May, Data to support an anecdote about decreasing organic matter in the top 10 cm of putting greens with minimal coring or topdressing.

Thanks for reading!

Lists of the most popular posts from previous years are here:

• Top 10 posts of 2015 about fertilizer, green speed, soil tests, wind at St. Andrews, the 1/3 rule of mowing, U.S. Open at Chambers Bay, and foliar applications.
• Top 10 posts of 2014 about seasonal N use, control of turf diseases, an anecdote about ammonium sulfate, salesmen suggesting calcium, cool-season grass in the tropics, irrigation, and soil moisture.
• Top 5 posts of 2013 about summertime syringing to cool bentgrass, nutrient requirements, and potassium.
• Top 5 posts of 2012 about five articles every greenkeeper should read, 1 minute on fertilizer, the real price of fertilizer, and the imaginary problem of calcium deficiency.
• Top 5 posts of 2011 about modifying fairway conditions in Thailand, sandcapping or topdressing, weeds in Malaysia, and turfgrass potassium requirements.
• Top 5 posts of 2010 about zoysiagrass fertilizer, the China Golf Show, grass selection and manilagrass, Guidelines for Tropical Turfgrass Installation and Management, and turfgrass performance data at the Open Championship.
• Top 5 posts of 2009 about mowing patterns and grass color, core aeration, salt for weed control, seeded seashore paspalum, and turfgrass in Dubai.
  

I took 82 flights this year, for a total of 221,494 km (137,000 miles), and I've just mapped them. That's more than 5 times the circumference of the earth. Routes flown once are more blue, and the routes flown more often are more red.

That's more flights and more km than in 2015, when I flew 54 times for 186,056 km. A map of 2015 flights is here. It's been another extraordinary year for studying grass around the world.

Festuca and Agrostis in Washington

Native grasses at BKK when it hasn't rained for months

Organic matter accumulation from Zoysia japonica above a sand rootzone in Japan

Creeping bentgrass practice green with lots of target flags in Girona

Puccinellia maritima (I think that's the species) near Reykjavik

Poa pratensis at Kashima Soccer Stadium

Zoysia japonica and Zoysia matrella in Japan

Fine fescue in Nebraska

A rare first edition of Short Grammar of Greenkeeping in Kyoto

If you want to see more photos, have a look at the ATC photos on Flickr, or scroll through the @asianturfgrass media tweets.

You can find the treemap here.

This was a follow-up to my analysis of the 30 countries that sent the most visits to the blog this year. I thought it would be interesting to show the number of golf holes per country all in one chart, so I made one. The full interactive version is here, with a static screenshot pasted below.

That arrived in my inbox recently, plus a few questions about calculating K requirements using the MLSN guidelines, and whether if there are minimum levels, are there optimum levels too? Here's how I answered.

It sounds like you are on the right track. Here's a few general remarks based on what you described/asked:

If the lowest K on that course's greens is 57 ppm, you are great. You are mostly Poa on those greens, right? The grass will use about twice as much N as it does K. Therefore, my suggestion is to apply half as much K as you do N, and that should keep the soil at about that level well above MLSN. Check a year later and see if the trend is going up or down. If going up, you can cut the fertilizer, and if going down you might increase it. What you are basically doing is applying 100% of what the grass is using plus you are keeping a nice reserve in the soil. That is a safe way to do it and it is not gratuitous overapplication.

For the other courses, it makes sense to let the numbers get a little closer to the MLSN minimum. I would make the calculation based on the soil test and the expected N application rate. The 22 ppm change in soil concentration is correct for a pound, if you are thinking of a 6 inch deep rootzone. For putting greens -- actually for most mowed turf in general -- I think of the rootzone as being 4 inches. In that case you can expect a pound of application per 1000 ft² to increase the soil by 33 ppm. You can expect the harvest of a pound per 1000 by the grass to reduce the soil by 33 ppm.

If you apply 4 pounds N, expect the grass to harvest about 2 pounds K (50% K use compared to N). MLSN at 37 ppm is about 1 pound of K. That's always going to be there in reserve; we don't want the soil to drop below that. If you have a soil test at 45 ppm, then the way to calculate a fertilizer requirement is like this.

Amount needed is amount to keep in reserve (the MLSN minimum) plus the amount the grass will use minus the amount actually present. I'm going to say you calculate this for a 4 inch rootzone depth and you will apply 4 pounds of N.

That is 2 lbs of K use + about 1 lb K needed as the MLSN minimum - (45/37 = 1.2 lb in the soil now). That is 3 - 1.2 = 1.8 pounds of K required to keep the grass from dropping below the MLSN guideline. I suggest dividing that 1.8 pounds (your number is going to be different, I am just showing how I make the calculation) into as many apps as possible and then applying it through the season. Or, if you are applying 4 pounds N, then you have a 4 to 1.8 ratio of N to K, and just apply close to that ratio at every application.

It can be simpler than that, but that is the detailed work through of the calculations. The really simple way is if the soil is less than 50 ppm, apply N and K in a 1:1 ratio. That is bound to make the soil K go up, so you will be sure to be staying above MLSN. If the soil is in the 50 to 75 ppm range, apply 2:1, and that should keep the soil at a similar level. When the soil is above 75 ppm, so long as you aren't applying a ton of N, you probably can get by with little or no K.

I prefer to make the exact calculation. And then check the grass response to the fertilizer and adjust inputs accordingly.

Oh, is there an optimum? I don't think there is. I think there are problems if you get too low with any element, but once you move from "too low" to "enough", then all the benefits from that element have happened. The MLSN approach is designed to prevent you from getting "too low" and to make sure you are always in the "enough" range. Once there is enough, the problems are expected to be from traffic, or dry spots, or shade, or whatever. The idea with MLSN is to provide a framework to put every element in the "enough" range and then you can focus your limited time and energy on the other things that might be affecting turfgrass performance.

And these are the real ones this time, not the turf disease.

I was at Soi Dao Highland Golf Resort in Chanthaburi. This resort is surrounded by mountains near Khao Khitchakut National Park and Khao Soi Dao Wildlife Sanctuary.

I asked, "are there any elephants here?" There weren't any, but I was told the count is 11 elephants living in the adjacent forests, and that the occasional elephant comes onto the course. Here are elephant footprints at the edge of a pond on the course.

All the flags and all the rakes are collected each night to prevent elephants from playing with and breaking them. Apparently that was a problem in the past.

The course has impressive views and holes that border the forest and tropical mountain streams. The driving range is one of the best in Thailand. I wasn't sure if this was a driving range or a par 3 course. It could be both.

For more elephant footprints on turfgrass -- the real ones, and the fungal ones -- see:

• A turfgrass mystery on seashore paspalum in Tamil Nadu
• 'Tis the season

Visitors to the ATC blog in 2016 have come from 153 countries. Of course some countries have a big population, and lots of turfgrass, like the United States, so I would expect a lot of visits from there. Can I check which countries have relatively more or less visits than expected? Such a calculation is an indication of where this blog is unusually popular (or unpopular!).

To do that, I went to Google Analytics and downloaded the number of visits for the 30 countries that sent the most visitors to the site. This table shows them sorted by number of visits. I then made two calculations. One was to express the total visits in terms of each country's population. The second calculation was to express the total visits from each country in terms of the number of golf holes in that country.

The data are shown in this table, and you can click the column headers to sort by that column. The United States sent the most visits in total, Iceland had the most visits based on population, and Hong Kong had the most visits per golf hole.

After making these calculations, I plotted the ratios against each other. To spread the points out on the chart, I made the chart using the square root of each ratio. This shows how the 30 countries that sent the most visits are related to each other in terms of visits per population and visits per number of golf holes.

I was glad to see so many visits from all over the world this year, and to find which countries sent more visitors than expected based on population or number of golf courses. This could be good for marketing!

If you are reading this in Iceland, Ireland, Canada, Mauritius, or New Zealand, your country sent more visits to this site than expected based on population. And if you are reading this in Hong Kong, Singapore, Mauritius, the UAE, or the Philippines, your country sent more visits to this site than expected based on the number of golf holes in the country. Based on that, you might be interested in my book, A short grammar of greenkeeping.

Or, you might consider inviting me to your country for a turfgrass seminar. Since Mauritius is near the top on both of those lists, let's try to make that happen!

No, I'm not talking about the stimpmeter. And this tool will probably only be useful for a few people. In fact, the tool is probably not what you think it is. But this story may be of general interest.

I'm quite interested in putting green speed. I've written numerous articles about green speed and variability in the measurements for ゴルフ場セミナー. In English, you can read this report about some of the measurements I've made.

What I find more and more interesting is the variability in putting green speed. Not so much from course to course, or day to day, but more so from green to green on the same day, or from location to location on the same green.

When the average of 18 different greens is 11 feet, what is the range of measurements on individual greens? Is it from 9 feet to 13 feet? Or is it from 10 feet 8 inches to 11 feet 4 inches?

As usual when studying this topic, I found myself studying Thomas Nikolai's A superintendent's guide to putting green speed.

That led me to Radko et al. on A study of putting green variability.

So here is where the extremely useful tool comes in. I wanted to get the data from the article, to make some calculations of my own. So I turned to the WebPlotDigitizer. This has been an extremely useful tool for me in the past, and I was glad to use it again today to study variability of putting green speed.

With those data from the chart now in a file I can work with, I've been able to make a number of calculations.

And how about those green speeds in 1980?

I feel like there is something not everyone understands about the quantity of fertilizer recommended by the MLSN guidelines. A question came up in my Twitter feed this morning, and I wasn't sure if it was about implementing MLSN, or not. It certainly seems to be a common concern, something along the lines of "how can I be sure that I'm supplying all the nutrients the grass needs?"

No matter what kind of grass you are growing, or in what climate, the calculation of nutrient requirement using the MLSN guidelines has already accounted for 100% of the nutrients that the grass can use.

The calculation of how much of each nutrient to apply, based on the MLSN guideline, is basically the same as the Precision Fertilisation method of STERF. The one difference is that the MLSN approach considers the quantity of nutrients in the soil.

If the nutrient content in the soil is a lot more than the grass can use, then none of that nutrient will be recommended as fertilizer. If you are not familiar with the calculation, see this presentation on the MLSN guidelines and specifically look at the equations on slides 4 and 5.

The STERF approach is to apply 100% of what the grass uses, no matter what the soil content is. That is sure to work well. The MLSN approach is to make sure the grass is supplied with 100% of what it can use plus keeping a buffer of nutrients in the soil that will never be touched. That buffer is the MLSN guideline level. Because MLSN considers the nutrients in the soil, when the soil nutrients are more than the amount the grass can use, while still keeping enough in reserve to stay above the MLSN guideline, none of that element will be recommended as fertilizer.

Either way, the grass is supplied with more than 100% of the nutrient it can use.

For more about this, see:

• Does stressed turf require more nutrient supply, or less?
• 2 similar approaches to fertilization, with 1 notable difference
• Questions from a correspondent
• "I'd be applying potassium all the time": part 2
• MLSN webinar on TurfNet

A little aside here -- I receive way more inquiries about MLSN and turf management in general than I can answer in any kind of detail, or at all. I appreciate all the interest and questions, and thanks to all these questions I have continuously expanding GNU Emacs files entitled blog_posts.org, data_analyses.org, and writing.org. If I haven't answered your question, it's in one of those files for future attention.

When I saw that Brad Revill had started a blog, I was intrigued, because there are not many blogs written by turf managers in the tropics. I was even more intrigued when I saw that the title of his very first post was The start of something new -- MLSN!!. He wrote:

For years I have been following the recommendations from soil testing laboratories trying to create the "ideal soil" with the correct ratios of nutrients. After each soil test I would follow the recommendations, most of the time adding more and more calcium. After each test my ppm values would increase along with the "target" ppm values which kept getting higher and higher until it seemed I would never reach it. I grew frustrated with the recommendations and after reading article after article and research papers online, I came across the MLSN guidelines produced by Pace Turf and Dr. Micah Woods.

That's a new blog that I expect will be quite interesting to read.

Now for my annual reminder of an excellent resource, the Golf course management blogging world site. This site aggregates blogs from around the world and shows the most recent updates at the top.

The site administrators sometimes make manual updates to confirm the feeds are correct and the code is updated. I'm hoping they will do a refresh on the site again this winter to make sure all the feeds are active.

And one more thing. If you are really wanting to read about turf, I have updated my last blog post about an eclectic reference list, so that each article or book that I cited now has a link to the item. I cited articles from 1859 until 2012, and you can get the full text of most of the items for free. Have a look, and see if you find anything interesting.