Soil

An MLSN Refresher

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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.

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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.

Activity

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

Figure1

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

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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.

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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 c1.staticflickr.com

image from c1.staticflickr.com

image from c1.staticflickr.com

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.

Lpercent_table7

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.


Both of these are worth your time

One is an article, another is a podcast, and you won't regret the time spent reading the first and listening to the second.

First, the 4 November issue of the Green Section Record contains Managing Organic Matter in Putting Greens by Adam Moeller and Todd Lowe.

This article explains that "there are many agronomic programs that influence the playability and health of putting greens, but organic matter management is arguably the most important." It goes on to explain the standard practices in 2016.

Moeller and Lowe conclude that "traditional programs", and by that they mean programs that include core aeration, "still provide the most consistent results for managing organic matter and improving putting green conditions."

This is a really good article for referencing what is standard in 2016, but I'm not in full agreement with their conclusion. I used to think that coring was essential, but over the past few years I've changed my thinking. More about that in the footnote.

The second item is the recent TurfNet Radio podcast with Frank Rossi and Chris Tritabaugh about managing for the Ryder Cup. If you listen to this, you will find that they discuss organic matter on putting greens (and a lot of other interesting things), but if you haven't heard, there has been no core aeration on the greens at Hazeltine since 2013.

The article says coring provides the most consistent results, and the podcast explains how greens are managed to a high standard without coring. It's good to be informed about this topic, so that you can be sure to make the right choices for any turf that you manage.

Footnote: I used to recommend the removal of 20% of the putting green surface area by coring each year and the annual addition of at least 12 mm of sand topdressing. I don't make that recommendation anymore.

Rossi and Tritabaugh talked about the grass yield and growth rate. How much was the grass growing? The idea being that one can match the quantity of sand applied to the rate of grass growth, thus avoiding coring by maintaining a consistent organic matter content at the soil surface. But they did not put a number to the growth rate. I think it is possible to put a number to the growth, and from that to make a site specific plan for organic matter management.

Consider the "new" bentgrasses with high shoot density, or ultradwarf bermudagrasses, widely considered to be prolific thatch producers. Please consider now how much thatch bentgrass will produce in Bangkok, or how much organic matter Miniverde will produce in Moscow. None, right? Now please continue that thought experiment a step further, and consider how much thatch (or organic matter) grasses produce when they grow slowly, supplied with just enough nitrogen and just enough water to produce the desired growth rate. Supply no N and no H2O to ultradwarf bermudagrass and there won't be any organic matter to manage. Is it possible that there is a level of growth at which minimal topdressing and no coring produce the desired surface? That's the goal, and I think it is possible with careful attention to the growth rate.

And that avoids (or at least minimizes) the putting surface disruption associated with coring too.

For more about this, see:

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Fast release fertilizer, fertilizer burn, and root growth

I gave a seminar in July in which I discussed how much one can expect grass to grow.

I said something like "grass can always grow more, but turfgrass managers restrict the growth rate by supplying less nitrogen fertilizer than the grass can use. For example, I could apply 100 g/m2 of 10-10-10, and the grass would grow more rapidly than if I applied only 10 g/m2."

Someone in the audience disagreed with me. "You can't apply 100 g/m2 of 10-10-10," he said. "That much will burn the grass."

I wondered about that, so I went shopping for 10-10-10. I didn't find a 10-10-10 with suitable particle size. The closest analysis with a particle size suitable for application to turfgrass was 14-14-14. I bought a bag.

Then I marked out plots on a korai (Zoysia matrella) nursery. Each plot was 1 m by 1 m, and there were seven plots in total.

This is what the plots looked like right after the fertilizer application, before turning on the irrigation, on 31 July 2016.

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I had measured out the 14-14-14 fertilizer and applied it to these plots. One plot received no fertilizer, and the other plots had 14-14-14 applied at rates from 2.5 up to 15 g N/m2 in 2.5 g increments (that's an N rate of 0 to 3 lbs N/1000 ft2 in 0.5 pound increments).

This is what the plot receiving the 15 g N/m2 rate looked like after I spread the fertilizer and before irrigation was applied.

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I wanted to check three things with these fertilizer treatments.

First, I wanted to see if this much fast release fertilizer would burn the grass. In the seminar, I'd said that 100 g/m2 of 10-10-10 could be applied, but no one would do that, because it would make the grass grow too fast. In this test with 14-14-14, I included N rates all the way up to 15 g/m2, equivalent to 150 g/m2 of 10-10-10.

Second, I wondered what would happen with root growth at different rates of fertilizer.

Third, I wondered how long a color or growth response would last. For example, when the grass starts going dormant in the autumn, would the effects of a 31 July fertilizer application still be visible?

Before I applied the fertilizer, the roots were like this. These roots are from the plot receiving the highest rate of 14-14-14, before any fertilizer was applied.

Roots31july

The fertilizer was watered in and there was no burn. Maybe just a little bit where a few particles didn't dissolve completely, but the overall effect was to make the grass greener. A week after the fertilizer application, the plots looked like this. In the foreground is the plot with no 14-14-14 applied, and each plot after that received an increasing 2.5 g N/m2 increment of 14-14-14.

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This plot received 15 g N/m2. A week after the application, it was greener than the surrounding grass that didn't receive fertilizer. If there was any burn, one might pick out a few leaves here. They didn't last long.

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 I came back a month later and had a look at the plots on 30 August.

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I also looked at the roots for each of the fertilizer treatments. I had expected that adding some 14-14-14 would cause an increase in roots. All the plots showed an increase in roots by 30 August compared to the roots I looked at on 31 July. But I don't see any increase in roots with fertilizer application. If anything, the root system was largest in the control plot that received no fertilizer.

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The soil on this nursery is similar to the soil on the course. The nursery soil wasn't tested, but the course soil was, and in May 2016 the median pH was 6.4. Using the Mehlich 3 extractant, the mean K, P, Ca, and Mg were 59, 172, 1304, and 57 ppm.

All these elements were present at adequate amounts in the soil, so adding more K and P in the 14-14-14 didn't make the roots grow more. I had expected more N (up to a point) would cause an increase in root growth, but after one month, that's not apparent at all.


MLSN and the probability of a response to fertilizer application

Travis Shaddox shared an impressive list of quotes about BCSR. Some key words from those quotes include irrelevant, inefficient, pseudoscience, should not be used, and NOT recommended.

Instead of BCSR, Allan Dewald asked about MLSN, and Travis mentioned that MLSN doesn't provide a response probability, but maybe that is coming.

We won't provide a response probability for MLSN because it is not a fertilizer calibration. These are two different things.

MLSN is a method for interpreting turfgrass soil test results, based on an analysis of thousands of soil samples in which turfgrass is producing a good surface. MLSN is developed from thousands of soil test results in which turfgrass performance was fine.

This is a paraphrase of what we wrote in the MLSN preprint:

Traditional soil test calibration for turfgrass is impossible and will never be done. It is impossible because turfgrass is a global crop, with many species and varieties used, in thousands of soil types, in every possible climate, across a range of turfgrass performance requirements. MLSN is a method which allows turf managers to ensure their turf is always supplied with enough nutrients.

For the full details of what MLSN is, and to see the data supporting it, please read the paper.

Now to elaborate on why I think probability of a fertilizer response is not the right way to do calibration for turfgrass, and why MLSN works even though it is not a traditional fertilizer calibration.

Calibration is based on classifying soils with different levels of nutrients into categories based on probability of yield response. For full details, see Chapter 14 by Douglas Beegle, Interpretation of Soil Testing Results, in Recommended Soil Testing Procedures for the Northeastern United States.

The classification into probability of response, according to Beegle, involves three categories. In the below optimum category, also called very low, low, or medium, "the nutrient is considered deficient and will probably limit crop yield. There is a high to moderate probability of an economic crop yield response to additions of the nutrient."

In the optimum category, also called sufficient or adequate, "the nutrient is considered adequate and will probably not limit crop growth. There is a low probability of an economic crop yield response to additions of the nutrient."

The third category is above optimum, also called high, very high, or excessive. In this category, "the nutrient is considered more than adequate and will not limit crop yield. There is a very low probability of an economic crop yield response to additions of the nutrient."

In turfgrass management, one is not trying to maximize economic crop yield. Rather, one is trying to produce the desired surface performance, and does that by modifying the growth rate of the grass.

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I wrote about this in A Short Grammar of Greenkeeping.

When modifying the growth rate of the grass, one is often trying to minimize the growth rate. Let's try anyway to apply these probabilities of response to turfgrass.

If we take the categories for probability of response, as defined by Beegle, we notice that he has referred to crop yield and to an economic crop yield response. Let's drop that and substitute turfgrass performance and turfgrass performance response. Now we have a definition that makes sense for turfgrass.

Below optimum: The nutrient is considered deficient and will probably limit turfgrass performance. There is a high to moderate probability of a turfgrass performance response to additions of the nutrient.

Optimum: The nutrient is considered adequate and will probably not limit turfgrass performance. There is a low probability of a turfgrass performance response to additions of the nutrient.

Above optimum: The nutrient is considered more than adequate and will not limit turfgrass performance. There is a very low probability of a turfgrass performance response to additions of the nutrient.

I think it is impossible to do soil test calibrations for every grass, climate, soil, and turfgrass use combination. So how can we figure out some way to interpret turfgrass soil tests and assign the results into one of those three categories? That's where MLSN comes in.

What we did with MLSN was look at thousands of soil test results from the optimum and above optimum categories. The turf was performing well at the time the sample was collected, so the soil was unlikely to be in the below optimum category.

Then we studied the distribution of the nutrient levels in those soils, threw away the bottom 10% to make sure we have some buffer against being too low, and identified the MLSN guideline as the level in the soil that we don't want to drop below. Nutrient recommendations are then made to ensure the soil doesn't drop below that minimum.

Because the soils used to identify the MLSN guidelines were already in the optimum or above optimum category, there is an implied probability in the MLSN recommendations. That is, keeping the soil from dropping below the MLSN guideline is the same as keeping the soil at a level with a low to very low probability of a turfgrass performance response to additions of the nutrient.

Although such probabilities are implicit in the MLSN approach, we do not use those terms or classify soils into categories. With MLSN, we have just two categories -- enough, and not enough. Turfgrass is a perennial crop, and soil nutrient levels go down as the turf harvests nutrients from the soil. The MLSN fertilizer recommendations consider how much of an element is in the soil now, how much of that element the grass will use over time, and then makes a recommendation to provide enough of that element to meet all the grass requirements.


Soil temperature and fairway management from 1980

I don't recall what I was searching for, but I stumbled fortuitously across this article by Oscar Miles from the Green Section Record in 1980:

Soil temperature and related fairway management practices -- northern turfgrasses

It's a great read, and quite interesting to see how he anticipated so much of the maintenance as conducted today.

"The additional data, I believe, will help us set up a program that a data processor or computer can maintain for us. I feel it is inevitable that mini-computers will make their way into golf course management systems. This is not as far-fetched as you might think."

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p.s. Now I recall. I probably was searching for something related to soil water content and nighttime soil temperatures in summer.