"Sorry if this is a rubbish question"

This question came some months ago:

"I'm just pondering something about MLSN levels for Bent vs Poa and so hopefully you can clear it up.

Having seen a bit of research coming out about k levels affecting disease pressure differently for poa and Bent does that not mean there should be two different MLSN's for the two species?

Sorry if this is a rubbish question, I might have missed something somewhere."

That is not a rubbish question. There are three general points I'd like to make about this.

  1. MLSN is a method for interpreting soil tests to prevent deficiency. That is, MLSN is designed to be conservative. The MLSN guideline serves as a quantity of K in the soil that the grass will never touch. The amount of K recommended as fertilizer using the MLSN approach differs based on three things: grass type, growth of the grass, and the quantity of K in the soil. The fertilizer recommendation for K changes for every situation, but the MLSN guideline remains the same.

  2. This article by Doug Soldat has more about varying K fertilizer amounts and bentgrass and Poa annua diseases. If one wants to adjust the K fertilizer in an attempt to incite or suppress anthracnose or snow mold, or winter kill, then one might err on the side of a little bit more K for Poa in summer, and a bit less K for bentgrass, especially in autumn.

  3. MLSN is meant to be simple, and is meant to answer two questions. Is this element required as fertilizer? If the answer to the first question is yes, then the second question it answers is "how much of the element is required?" It is meant to err on the side of recommending too much, rather than too little. One can use those recommendations as a reference, and then if one wants to try to reduce the intensity of snow mold, then cut the K.

No matter how much sodium one puts into a sand rootzone, the soil structure cannot be affected, so gypsum won't be required


I received this question about leaching salts from the rootzone:

"I remember talking to you once before regarding flushing excess salts from the root zone and the application of gypsum or other calcium products before the flush and you telling me it was not necessary. I have since discovered that same conclusion for myself. I remember you sent me an article or a link to one of your blogs but I can't seem to find the email or article. Could you please send it to me again?"

I wrote back:

I don't recall that I've written anything specifically about that. I have written about Ca not being required in sand rootzones for the purposes of dealing with sodicity issues, because no matter how much sodium one puts into a sand rootzone, the soil structure cannot be affected, so gypsum won't be required. Relevant blog post:

Is sodium an imaginary problem?

Also, this: water and soil handout.

I have made a note to write a blog post [and here it is] about leaching salt from sand rootzones and Ca not being required. I'll do that sometime.

Real quick, water problems are divided into 3 main categories, and each has a different solution.

Salinity -- this is the total salt. The solution to salinity problems is to add extra water to leach the salts below the rootzone. No Ca is required for this. The water does the leaching.

Sodicity -- this is a soil structural problem that occurs in soils when the sodium gets too high. It is defined as exchangeable sodium percentage > 15%. This is irrelevant in sand rootzones because the sodium does not cause any structural problems in sand. This is a problem in clay soils. The solution to this problem is to add gypsum. The Ca in the gypsum then replaces some of the sodium and restores the soil structure.

Saline-Sodic -- in this case, the sodicity occurs and is combined with high total salts. Also irrelevant in sand rootzones because of reason mentioned above. The solution to this problem is to add gypsum, to restore soil structure, and then to add extra water to leach the salts.

Of turf, roots, and fertilizer

I'd like to make three points.

1- Surfaces can be great, and the roots can be negligible.


If the objective of greenkeeping work is to produce the desired surface, then one only needs enough growth to produce that surface. One also only needs enough roots to produce that surface. Any aboveground growth beyond that required to produce the surface is unnecessary, even problematic. For roots I won't go so far as to say extra ones are problematic, but I might say roots beyond those needed to produce the desired surface conditions are irrelevant.


2- Surfaces can be awful, and roots can be amazing. I've seen some incredible roots on some surfaces that didn't come close to meeting the level desired.



I'd rather have good surfaces than amazing roots.

3- I've been reading about an increase in roots and a simultaneous reduction in organic matter. Jerry Kershasky and I had a recent conversation about this:

Let's say one generates massive roots. Like those on the poor surfaces in section 2, above. Or by increasing the N rate (an easy and underrated method for stimulating root growth) as shown in the precision fertilisation guide from STERF.


How can one generate massive roots and at the same time reduce soil organic matter over time? I suggest it is impossible to do both. In the short term I can see where one can do that -- I've seen it myself. But long term, how can increasing the organic matter through production of more roots than would otherwise be produced lead to less organic matter in the soil? I'm not that credulous.

"It has been around 8 months since we started following the MLSN guidelines and ..."

Brad Revill wrote about his use of the MLSN guidelines, some of the adjustments he has made, and reports on how it is working.

"So it has been around 8 months since we started following the MLSN guidelines and we have been very happy with the results, not just from a turf performance point of view but from the financial side as well!"

That's the idea. Turf performance should be the same, or better, than with other methods, because MLSN recommendations are based on supplying the grass with all the nutrients the grass requires.

"Some of you may be asking 'What about root growth?' Well I can only tell you from my experience following the MLSN over the past 8 months is that we have seen a steady increase in root depth over the last 12 months"

I'm glad to hear that. Eli Rahz shared something similar last week:

And for cool-season turf, I'm reminded of the Poa annua roots Sue Crawford showed last autumn:

Good stuff. It's fun to see those results.

An MLSN Refresher


Not everyone understands how the MLSN guidelines work. I saw a recent conversation started by Andrew McDaniel followed by a number of posts from STSAsia exhibiting confusion on the latter's part about the use of the MLSN guidelines.


To paraphrase Brian Ripley, "Once you appreciate that you have seriously misread the guidelines, things will become a lot clearer." I'll take the opportunity here to write a short refresher about MLSN.

The grass is growing in soil. That soil has a certain amount of nutrients in it. We determine that quantity of nutrients by doing a soil nutrient analysis (a soil test). The amount of nutrients in the soil will change tomorrow, and the next day, and into the future, based on how much we apply as fertilizer, and based on how much the grass uses. But we can use this number. I'm going to call this soil number C. That's the quantity of a nutrient measured by the soil test.

On its own, that soil test number isn't useful for anything. I need to compare it to something. How about comparing the amount of a nutrient in the soil to the amount of a nutrient the grass will use? Now I am introducing a time component, because the grass use during 1 month of dormancy is different than the amount of grass use during 1 month of active growth. And the amount of use for 1 day is different than the amount of nutrient use in 1 year. And as STSAsia pointed out, the use is different in different locations. And the use is different for different grasses. Use of the MLSN guidelines explicitly accounts for the expected use of nutrients at any location. Let's call the expected use by the grass A.

Now we have two quantities. We have A, which is the amount the grass will use. And we have C, which is the amount in the soil. It would seem that this is enough information to determine a fertilizer requirement. We could say if A is more than C, then we definitely need to add the difference, because otherwise the grass will use more than the soil has. And we could say that if A is smaller than C, we don't need to add that element, because the amount the grass will use is less than the amount in the soil. And that is sort of how it works, but the MLSN guideline adds a buffer of extra nutrients that the grass will never touch.

The MLSN guidelines are added to the amount the grass will use. We can call the MLSN guideline amount B. The amount B is a quantity of nutrients that we always want to remain in the soil, untouched by the grass. So we take A, the amount the grass will use, and add to it B, the amount we want to keep as a reserve in the soil. We then compare A + B to C, and that difference becomes the fertilizer requirement. In that way, the site specific and grass specific and climate specific characteristics of each location are considered, and then an appropriate fertilizer recommendation is made. This fertilizer recommendation for each nutrient is based on how much the grass will use at each site, it accounts for keeping a reserve of nutrients in the soil (the MLSN guideline), and for how much of an element is actually in the soil at the time of sampling.

paceturf made the calculations for nutrient requirements at Fukuoka and Kuala Lumpur. Although the MLSN guideline is the same at each location, the nutrient recommendations will be more than 4 times higher for Kuala Lumpur than Fukuaka.

The MLSN guideline values are the only thing that stays the same. These represent a buffer amount of nutrients in the soil that we don't want the grass to use. Then the site specific values for estimated grass use of each element, and for the actual soil test at that site, make the MLSN approach suitable for just about every environment.

For more, see:

Aluminum and soil pH in 3,010 soil samples

Even though high quality turfgrass can be produced below a soil pH of 5.5, for standard situations I will recommend keeping soil pH at 5.5 or above. Soluble aluminum will be negligible above pH 5.5. Below pH 5.5, there is a lot more soluble aluminum, and this can damage roots. A second reason for keeping the pH at 5.5 or above is to make sure the growth of fungi and bacteria in soil proceeds without too much restriction. These fungi and bacteria decompose organic matter, and I'd rather not restrict that too much with low pH.

I was writing an article about this, and I wanted to make a chart to show how the aluminum is high at pH less than 5.5 and how aluminum is almost 0 above that pH. I wanted a quick set of data to make this chart, and I remembered that I had a file with 3,101 soil test results as part of the MLSN project. Of those samples, 3,010 had 1 M KCl extractable aluminum data, and all had pH. So I plotted the relationship between pH and aluminum, and I did it in two different ways.

The soil pH was measured in the standard way, with 1 part of soil mixed with 1 part of deionized water, the solution is stirred, and then the pH is measured in the solution. The pH is the negative logarithm (base 10) of the hydrogen ion activity in the solution. If the hydrogen ion activity is 10-1, or 0.1, the pH is 1. If the hydrogen ion activity is 10-5, or 0.00001, the pH is 5. The higher the pH, the lower the hydrogen ion activity.

I wanted to see how the soil aluminum changed when plotted against {H+} directly.


That's not especially clear. But it is when those same data are plotted not as {H+} directly, but as pH.


Now with that chart it is clear that when pH is 5.5 or less, the aluminum might be high. When the soil pH is above 5.5, the aluminum will almost never be high, and thus will almost never be a problem.

Preventing nutrient deficiencies


The recording of my webinar on preventing nutrient deficiencies is now available in the videoteca section of the Campus del Césped website.

Or watch the English version right here.

This was fun. I hope you'll read the handout too. It is only 4 pages, with lots of white space, and gives a brief overview of this important topic. If you are still interested, then watch the video of the webinar at your leisure, and watch or download the slides too.

Links in English

Links in Spanish

This is a lot to fit into an hour

But I am going to try. I've got four things I want to explain in this upcoming webinar, and I have made some interesting calculations. Can calculations be provocative? Maybe these ones are provocative and interesting.

The Campus del Césped webinar is on 12 January at 17:00 Central European Time. You can register here.

Here is the 4 page pdf handout, in English.


These are the slides in English.

These are the slides in Spanish.

If you are are joining this webinar, you will find it useful to review the slides and handout prior to the event.

Sand, leading to more growth, needing more sand, leading to more growth, needing more sand

Frank Rossi and Dan Dinelli had an interesting conversation on Turfnet Radio. I learned a few things, and I even agree with some of what they discussed. But not all of it.

The first thing that came to mind when I heard them talking about sand and growth was lawns beside the ocean. More about that later.

If you jump to the 30:40 mark of the podcast, Dinelli says, "I'm convinced that the more sand we put down, the more biomass, the more organic matter we develop. And I know that is counterintuitive."

It sure is. Because I'm thinking of a lawn next to a beach, where windblown sand just keeps coming and coming. Or I'm thinking of the 7th hole at Sandpines in Florence, OR.

In the situation I'm thinking of, the sand is not a cause for organic matter development. Back to the podcast.

When asked about this, Rossi took his turn as the guest and answered that he would say there are two components to it. First, there may be nutrient or PGR programs that need to be addressed.

Then he said this about the bigger question on it:

"When you aggressively verticut you thin that stand and then you incorporate sand into it and I believe that leads to even more biomass production and that's the chasing the tail part ... you have to thin it out .. to make room for the sand, but by doing that, aren't you stimulating more growth?"

I don't think that's how it works. If it is, sand isn't the cause of it. And I don't think verticutting is either. Growth is affected by temperature, and light, and nitrogen, and water. Those are the primary things that influence it. Put simply, more of them and there will be more growth. Less of them, and there will be less growth.

So let's go back to the beach. Or to a lawn beside a sand dune. Let's hold N constant. We'll provide whatever you consider a miniscule N rate to our beachside or duneside lawn. We'll need to make sure the grass has enough water. Let's make sure the soil is kept just above the wilting point. The grass won't wilt, but that's all the water that is supplied. And let's set the temperature to be optimum for growth, and we'll make the light optimum too.

Now let's divide the lawn into three parts. One part has sand restricted from blowing across it. With that N rate and irrigation rate, do you expect a lot of biomass production? I don't.

But I'm pretty sure that part of the lawn protected from topdressing is going to have more biomass production than the second part of the lawn, where I allow sand from the beach (disregard any salt effects here, and just consider sand) or adjacent dune to blow across at topdressing rates throughout the season, depositing let's say 1.2 cm of sand over the course of the season. Remember, we are growing this grass with a miniscule N rate and irrigation just to keep the soil above the wilting point.

I think the section of my lawn where I restrict the sand completely is going to develop more organic matter. And then there is the third section of my lawn, where I don't restrict the sand at all. In that case I have a dune at the end of the season and the grass is dead, producing no organic matter at all.

If verticutting and sand topdressing are producing too much organic matter, please consider what would happen if you continued to verticut and sand topdress while stopping all fertilizer and all irrigation. The organic matter production would stop, because the grass would die.

Here's the kind of situation I'm thinking of. These are all manilagrass (Zoysia matrella). Some people think of this species as having heavy thatch.

image from

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Plant it beside a beach, give it a very slow growth rate, and then add sand, and you get no thatch at all. You do get something that would probably be a better turf if less sand were added to it.

Isn't the growth rate largely a fertilizer (especially N) and a water issue? I don't see how sand and verticutting cause the grass to grow more.

"Maybe those that soil test are just more likely to fertilize in general?"

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

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.