High soluble salts, K, and extractants

Earlier this year Brad Shaver and I had a discussion about salinity and extractants.

I had written previously this post explaining that a saturated paste extract is not a good way to look at soil nutrients and that it is not a good idea to look at a saturated paste extract and compare it to a standard soil test.

Brad asked about potassium (K) in saline soils, about acid extracts overestimating exchangeable K in saline soils, and alluded to a continuing confusion about the combination of high soluble salts in soil, potassium, and different extraction methods.

I’ll explain this in two ways. First briefly, without all the details.

Saturated paste (I’ll abbreviate as SPE for saturated paste extraction) is not useful to evaluate K in soils with high soluble salts because the problem with saline soils is too many soluble salts. The solution to this is leaching of the salts. The K measured by the SPE will be deliberately leached, and depending on how saline the soil is, a large portion of the K measured by a standard soil test, because it measures soluble and exchangeable K, will be deliberately leached as well.

Because one is going to deliberately leach soluble salts from a saline soil, as part of the standard management of saline soils, it doesn’t make sense to use the soil test K, from any extraction method, to determine how much K to apply as fertilizer to saline soils.

What does make sense? There will be some K in the soil. There will be some K added through irrigation water. And in a saline situation one can supply K as fertilizer in the quantity that the grass can use, disregarding the soil K and the K added in irrigation water. This guarantees the grass will be supplied with more than enough K, and one doesn’t need to test the soil for K at all.

Now explained the second way, with a few more details, and some data.

The purpose of soil testing is to determine if an element is required as fertilizer, and how much of that element should be applied. Or, in the case of salt-affected soils, the purpose of testing is to identify the problem and to determine what actions should be taken to solve the problem. Of course, if there is a problem with soluble salts, and one leaches them, it doesn't make sense to try to make a fertilizer recommendation from something one is going to be removing from the soil.

There are two forms of plant-available K in the soil: soluble and exchangeable. A SPE measures the soluble K and a small amount of exchangeable K. A standard soil test, such as the Mehlich 3 or normal ammonium acetate extractions, measures the soluble K plus the exchangeable K. Both the SPE and the standard soil test measure the soluble K, and the standard test will additionally measure exchangeable K.

Here are data from nine sites with the electrical conductivity of the saturated paste extract (ECe) labeled as (ec), the K in ppm by SPE labeled as (kh2o), the K in ppm by Mehlich 3 labeled as (km3), and the location of the sample.

ec kh2o km3 location
4.5 59.0 89 Thailand, fairway
17.4 110.0 118 Thailand, fairway
0.2 6.8 51 Philippines, green
0.1 4.4 215 Philippines, fairway
0.2 10.5 82 Philippines, green
0.3 14.8 55 Philippines, green
0.3 17.1 74 Philippines, green
0.9 45.0 174 Thailand, green
0.9 20.8 38 Philippines, beach

I've marked the ECe = 4 dS/m level with a red line, to show in which cases a soil would be considered saline, and in which it would not. Note that one will try to maintain a site-specific ECe depending on the species being grown and the irrigation water salinity -- the 4 dS/m level is included here as a reference level. These samples represent a range of soil salinity levels, most not saline, and two of them saline. Let's look at what happens with soil K across this range of soils and salinities.

Kh20_vs_ecThe K extracted by SPE, which I have labeled as KH2O to indicate it was extracted by water, is low when the ECe is low, and it increases when the ECe is higher. That is to be expected, because the quantity of soluble K is expected to be a function of the soluble salt content of the soil.

Now we can look at the Mehlich 3 K (KM3) for these same samples.

Km3_vs_ecThis looks a bit different, as it should, because the Mehlich 3 test is measuring both the soluble K and the exchangeable K. When the soil salt content (the ECe) is low, then the KM3 is going to be influenced by the cation exchange capacity of the soil and the quantity of K on the exchange sites, and when the ECe is high then there will be a greater proportion of soluble K as part of the the K measured by Mehlich 3.

This next chart demonstrates that. In each of these samples, the KM3 is a larger value than the KH2O. That is because the Mehlich 3 test measures soluble and exchangeable K, while the SPE test measures only the soluble K. By looking at the difference between the KM3 and the KH2O, we can see that the more salt there is in the soil, the smaller the difference is between these two quantities.

Difference_km3_kh2oIs this making sense? When salt in the soil is low, which is what we want, there tends to be a big difference between the quantities of K extracted. As the salt in the soil increases, the difference gets small, because the quantity of soluble K is very high compared to the amount on exchange sites -- at least in a sandy rootzone.

Slight tangent for a moment -- this is something I've written and talked about before, as something that one should not be bamboozled by.

One wants to have low soluble salt content in the soil. When there is low soluble salt content, it is normal to have a large difference between the water soluble and the exchangeable nutrients. But that doesn't mean the grass won't be supplied with enough nutrients. From Environmental Chemistry of Soils (McBride, 1994): "Ion exchange reactions at surface sites exposed to solution are extremely fast."

Back to the data, now looking not at the difference between KH2O and KM3, but the ratio between them. Remember, KM3 in these data is always larger than KH2O, because KM3 contains both the water soluble (KH2O) and the exchangeable K.

Kh20_vs_km3_by_ecWith this proportion, when it is close to 0 (on the y-axis), that means the KH2O by saturated paste is only a small amount of the KM3. At low soil salinity, that's just what we see. And with increasing ECe, as expected, the proportion of soluble K increases.

This can also be represented in a linear relationship for these data by showing that same proportion of $(K_{H2O}) / (K_{M3})$ across the natural logarithm of ECe.

Kh2o_vs_km3_by_log_ecFrom this chart, it seems that knowing ECe and KM3 is enough to predict KH2O. Not only is the KH2O value not useful in making a fertilizer prediction because one will try to leach it away with the other soluble salts in a saline situation, but it can be predicted from other measurements, meaning it isn't adding any new information.

One to add to the reading list

Jim Brosnan's article from last week's Green Section Record is one you will want to add to the reading list, and after reading it, to your reference file. Entitled Golf's Most Common Weed-Control Challenges, Brosnan gives an overview of the particularly problematic weeds and the most current information about their control -- especially for warm-season or transition zone areas.


For more information about weeds, see the University of Tennessee's Turfgrass Weeds site.

MLSN around the world

On a recent trip to China, I was browsing through Golf People magazine and noticed a familiar article -- Using Minimum Levels for Sustainable Nutrition -- translated into Chinese.


You can download the Chinese version here.

This is the original article in English, from the January 2014 issue of GCM.

I also wrote an article on this topic for the Asociación Española de Greenkeepers (AEdG), which they have translated and published in their Greenkeepers magazine.

With Mandarin, Spanish, and English articles about MLSN and how to use the guidelines, this information is readily accessible to speakers of the world's 3 most used languages.

Temperature and light data from Fairbanks and Hilo for illustrative purposes

Temperature and light have a major influence on how ultradwarf bermudagrass will grow. I've shown the distribution of DLI at Tokyo and Watkinsville, and the DLI and temperature at Fukuoka, Tokyo, and Watkinsville.

Before going any further with calculations and combinations of light and temperature from transition zone locations, I thought it might be illustrative to show how these charts look for a couple non-transition zone locations -- Fairbanks, Alaska, and Hilo, Hawaii.

First, the temperatures. I've included Tokyo as a reference. Remember, Tokyo had an annual temperature, as represented by the cumulative sum of daily mean temperature in 2014, slightly more than Watkinsville, and slightly less than Fukuoka. All those cities, however, were pretty similar. Not so with Fairbanks and Hilo.

Temperature_3_disparateHilo has a tropical rainforest climate, and because the daily mean temperature is almost the same throughout the year, adding them together produces a straight line. Tokyo is the same as what was shown previously. And Fairbanks, where we won't be growing ultradwarf bermudagrass, has a cumulative daily mean temperature in 2014 that just barely stays above 0. The point of showing Hilo and Fairbanks is to point out what these charts would look like in a tropical situation, and in a subarctic one.

As an aside, one sometimes hears of ultradwarf bermudagrass being a big thatch producer, and requiring a lot of work for organic matter management. I would look at it differently, noting that any grass is going to grow at a different rate based first on the temperature and PAR at a location, and secondly based on the nitrogen and water supplied. Clearly, based on temperature alone, an ultradwarf bermudagrass would require no organic matter management in Fairbanks, because there would be no thatch production.

So Hilo is looking pretty good for ultradwarf bermudagrass, by temperature, and how does it look for light? Hilo is 19.7°N, Tokyo is 35.7°N, and Fairbanks is 64.8°N.

Hilo_disparate_dliInteresting. Fairbanks looks about like I would expect. That far north the DLI in winter is negligible. But how is it that Hilo just barely tops Tokyo for cumulative DLI? That's the effect of clouds, and it is why bermudagrass grows so poorly in Hilo. In fact, Watkinsville in 2014 had cumulative DLI of almost 12,000 -- more than the cumulative DLI in tropical Hilo.

I've mentioned previously the importance of light (DLI) when temperatures are close to an optimum for warm-season grass growth. The climate.asianturfgrass.com website has lots of charts and videos about that. 

In these recent posts, I've shown the temperature and the DLI separately. Coming up, I'll add one more transition zone location, and then see what happens when various combinations of DLI and temperature are made.

Monthly Turfgrass Roundup: July 2015

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

These are not mower stripes.

Jon Jennings shared this photo of what he calls the shortest par 5 in golf:

I wrote about leaching to manage salts in GCM China.

Golf course architect Paul Jansen says when it comes to course design and maintenance, less is more, for his column in HK Golfer.

Steve Isaac wrote about putting green playability in Golf Course Architecture.

Maximum daily wind speeds at RAF Leuchars: 1 chart, 609 July days.

Compared to other July days, how windy was in in St. Andrews on 18 July 2015?

Mean daily wind speed in July at RAF Leuchars, animated.

Photosynthetically active radiation as cool-season grass may see it.

Bjarni Hannesson collecting Global Soil Survey samples from Iceland:

I taught about the fundamentals of turfgrass maintenance.

The Golf Environment Organisation asks for your input on draft sustainable development standards.

Bill Kreuser shared a short review of syringing.

I taught about the principles of turfgrass nutrition and what not to do.

Jason Haines asked whether it might be better to water greens first.

Stephanie Wei says every golfer needs to play North Berwick:

Dave Wilber had a busy month on TurfNet Radio, speaking with Don Mahaffey, Chris Tritabaugh, and Andy Staples.

Andrew Gelman wrote about a really bad definition of statistical significance.

How is the daily light integral (DLI) distributed at two locations?

Combining DLI and temperature

At Kingarrock, the maintenance of the course attempts to replicate that of the 1920's.

Michael Bekken gives a report on playing Kingarrock.

I wrote about monitoring growth rate in GCM China.

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.

"One aspect of golf that we never promote is the health aspect"

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:

Combining temperature and light to compare location effect on turfgrass growth

The daily light integral (DLI) is the total amount of photosynthetically active radiation (PAR) at a location in one day. The DLI in an open (full sun) area changes with the latitude, time of the year, and cloud cover. There will be further reductions in DLI if there is shade from trees, structures, or mounds/mountains.

Nitrogen supply, plant water status, the DLI, and temperature all influence turfgrass growth, or even the ability of a particular species of grass to provide the desired surface conditions at a given location. With professionally-managed turf, the nitrogen and the water are controlled by the manager, so it is the DLI and the temperature left as the major factors, outside of the manager's control, that will influence the turfgrass growth.

I showed the distribution of DLI and how it differs from place to place. The implication of that, for ultradwarf bermudagrass, is that the place with higher DLI will be more suitable for the grass, and the place with lower DLI will require more actions to improve turf performance in shade, such as increasing the mowing height and reducing the N rate.

I was curious about the combined effect of temperature and DLI, so I looked up data for a few more locations. I'll make a series of posts about this, in each one describing what I've done. The previous distribution of DLI looked at Tokyo, and then Tokyo and Watkinsville, Georgia (near Athens), on the days in 2014 when the mean daily temperature was greater than or equal to 20°C (68°F). I pick that temperature because I expect ultradwarf bermudagrass can grow relatively well above that temperature, and will grow quite slowly below that temperature.

This chart shows Fukuoka, Tokyo, and Watkinsville, which had a similar number of days above that temperature in 2014 -- 150, 150, and 151 respectively. 3cityDensity

The distributions of DLI at each of these locations show that Fukuoka and Tokyo have more days with DLI less than 20, and Watkinsville has more days with DLI above 40. The median DLI at Watkinsville was 42.1, at Tokyo it was 35.8, and at Fukuoka it was 31.8.

What about the total DLI over the year? Rather than my arbitrary cutoff at 20°C, one can also add the DLI through the year. This chart shows the cumulative daily sum of DLI at these same 3 locations.


The cumulative sum of DLI was 9,139 at Fukuoka, 10,135 at Tokyo, and 11,736 at Watkinsville. Over the course of the year, there was more PAR at Watkinsville than at Tokyo, and more at Tokyo than at Fukuoka. This will have some impact on how ultradwarf bermudagrass would grow, and also on how the grass should be managed at each location.

What about temperature? I added together the temperature for each day at these same three locations, and the temperature doesn't vary as much between locations as the DLI did.


By adding together the temperature for each day, by the end of the year, Fukuoka has the highest total, then Tokyo, and then Watkinsville. The median annual temperature was 17.8 at Tokyo, 17.7 at Fukuoka, and 16.6 at Watkinsville.

With PAR, as represented by DLI, Watkinsville was highest, and Fukuoka was lowest. With temperature, as represented by the cumulative sum of daily mean temperatures, Fukuoka was highest, and Watkinsville was lowest. Can these be combined to get an index of growth, or an index of light and temperature affect on growth? I think so, and I will share some more calculations, and add in data for some other representative locations, in future posts on this topic.


An easy technique for monitoring the growth rate

Selection_017"Greenkeeping, at its core, is about controlling the growth rate of the grass. To get the desired green speed, or the maximum disease resistance, or the fastest divot recovery without too much thatch production, one must adjust the growth rate of the grass. An easy technique to monitor the growth rate is to measure the clipping yield from golf course putting greens."

That's what I wrote at the start of my turfgrass talk column in the July/August issue of GCM China. And I went on to explain just how easy this is, and more about why having a measurement of yield can be so useful.

"Beware! These topics are misleading and irrelevant"

Last week I led a seminar entitled "A discussion mostly about the principles of turfgrass nutrition, with a focus on soil nutrient analyses and their use in modern turf management." The slides for this seminar are available in English and in Japanese.

I usually talk about how one should do things, but in this presentation, I spoke for a while about how not to do things, with the list on this slide:

Why are each of these misleading and irrelevant?

The concept of locked-up nutrients
Nutrients in the soil may be relatively more or less available, but that is what a soil test evaluates. After a soil test (and a technical term for that is a nutrient availability analysis) has been conducted, one compares the test result to a guideline level. I recommend using the MLSN guidelines. Once the test is done, and the results are compared to the guideline, one knows the availability. That is all one needs to know. If nutrients are locked-up to the extent that the plant can't use them, that will be evident on the soil test result.

Focusing on what an element does, rather than how much is present
Phosphorus is crucial for root development, potassium is key to stomatal regulation, magnesium is at the center of the chlorophyll molecule, and calcium is essential for cell wall structure. All true, but also beside the point. What is important is that there is enough of each of those elements, not what those elements do. If there is enough phosphorus, all the root development benefits will proceed as they should. And so it goes for the other elements. The important thing to focus on is the quantity of elements available. Soil testing, and comparing the results to the MLSN guidelines, does just that.

Looking at percentages of elements rather than quantities
The quantity of an element available is what is important, and that will be expressed as either a concentration in the soil (for example as parts of element per million parts of soil -- ppm) or as a mass of element per surface area (for example as g m-2). Percentages of elements, or ratios of elements, don't provide the necessary information, and are not how one should look at soil test results. For more, see Nutritionism by John Foy and this review on cation ratios.

Water or saturated paste extracts to look at availability
The information in a water extract of soil is already contained in the standard (for example, Mehlich 3 or ammonium acetate extractant) test result. Take the same identical soil, divide into two sub-samples, modify the water soluble nutrients in one, and not the other, and then perform a regular soil test. The test results will show how the water soluble nutrients differ from one sub-sample to the next. A regular soil test already provides all this information. Water (or saturated paste) tests are good for research or for assessing soil salinity. They are not useful for determining how much fertilizer to apply. Carrow et al. wrote about this and offer this advice: "SPE [a saturated paste extract] is not the best method for determining soil fertility levels and can be very misleading."

The idea that an element can be exchangeable but not available
This is an insidious combination of 2 errors listed above: thinking of locked-up nutrients and the misuse of water extracts.

That's enough about how not to do it. For more about how to do soil testing, determine nutrient availability, and calculate how much fertilizer to apply, see:

Seeking input: GEO's proposed international voluntary sustainability standard for 'New Golf Developments'

The Golf Environment Organization (GEO) are seeking input from interested parties on their new golf development criteria. This is an exciting project, and you can read all the details here.

I encourage you to review the draft criteria for new developments and then send your comments to GEO. All the background and scoping information, the draft criteria, and the comments form are available at the new developments public consultation page on the GEO website.