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July 2015
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August 2015

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 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: