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.

"Do the MLSN guidelines use 17 essential nutrients?" a friend asked me last month. "I've found a couple good articles but couldn't really find a number on the MLSN website."

"That's an interesting question," I replied, "and I may answer it on my blog. I can explain the 17 and you'll be an expert."

Here's how it works, and how soil testing and the MLSN guidelines fit in. I'll describe this in four sections.

First, what is an essential element?

To be classified as essential, the element must meet three criteria, as described in a classic 1939 article by Arnon and Stout. An element is essential if:

1. a deficiency of that element makes it impossible for the plant to complete its life cycle.
2. the deficiency can only be corrected by supplying that element; the function of that element cannot be substituted by another.
3. it is directly involved in plant nutrition (plant metabolism), and is not merely correcting a soil chemical or microbiological condition.

Second, what are the essential elements?

Or more specifically, where does the 17 (or sometimes 14) number come from?

Well, we can start with carbon, hydrogen, and oxygen. These elements are what Carrow et al. call the basic nutrients. These elements are never required as fertilizer, because they are never deficient. The grass gets them from CO₂ and H₂O.

Then there are what are usually called the macronutrients. These are nitrogen, potassium, and phosphorus. These elements are often required as fertilizer.

Next come the secondary nutrients. These are still in the macronutrient range (more than 0.1% [1000 ppm] by dry weight), but are rarely required as fertilizer. The secondary nutrients are calcium, magnesium, and sulfur.

And then there are the micronutrients. These are used in small amounts by the grass, from less than 1 to 500 ppm in the leaves. The micronutrients are iron, manganese, copper, zinc, boron, molybdenum, chlorine, and nickel.

If you add all those up, the basic, macro, secondary, and micronutrients, you get 17 in total. That's where the 17 number comes from. Because the basic elements carbon, hydrogen, and oxygen are ubiquitous and are not applied as fertilizer, those three are often omitted from discussion and the list of essential elements is given as 14 in total. And occasionally there will be one of the micronutrients omitted; for example, the excellent Turfgrass Fertilization: a basic guide for professional turfgrass managers from Penn State omits nickel and gives the total as 16 elements. Which is fine, as I'll explain in the fourth section, below.

Third, do the MLSN guidelines use all 17?

Yes. And no. The MLSN guidelines provide a framework for ensuring that any grass, at any location, will be supplied with all the nutrients required by the grass. And yet the MLSN guidelines only list a minimum value for five elements: potassium, phosphorus, calcium, magnesium, and sulfur.

The MLSN guidelines are used to interpret soil test results. We don't soil test for the basic elements. Those are never deficient. And one doesn't make fertilizer decisions about nitrogen for turfgrass based on soil tests either, so we don't include nitrogen in MLSN (see N & MLSN, what's the connection). All the other macronutrients and secondary nutrients have a minimum guideline using MLSN. And we deliberately don't worry about micronutrients too.

Fourth, what about micronutrients?

I don't worry about them very much. I've explained this in detail in these two posts:

• Why I don't worry about micronutrients
• "Do you have a rough guide of all MLAN ranges for nutrients?"

Quoting from my comment in one of those posts:

the quantity of micronutrients the grass uses is so tiny as to be almost negligible. And we constantly keep the growth of the turf -- and consequently its demand for nutrients -- restricted by applying less nitrogen than the grass can use. Thus the probability of a micronutrient being deficient is very low ... Let's say grass uses 10 g N/m² per year. It uses progressively less K, then P, then Ca, Mg, & S. By the time we get to the most used micronutrient (Fe), we are looking at only 0.025 g/m² per year. 25 mg! And the other micronutrients are a fraction of that. In practical terms, there is almost no way a micronutrient can be deficient in turfgrass, and it is so easy and cheap to just spray out a complete micronutrient package at a tiny dose. There is really no need for soil testing for micronutrients in turf.

Which is why I think it is fine that the guide from Penn State omits nickel. When it comes to the micronutrients, the grass uses such a tiny amount that one doesn't have to worry much about them. And if you are worried about a micronutrient deficiency, or want to be especially sure that the grass has enough micronutrients, then it is easy and inexpensive to apply all the micronutrients that the grass can use. There is no excuse for a micronutrient deficiency.

Jon Scott wrote to me about my recent post on a poor way to fertilise.

"While this superintendent has solved his problem of nitrogen input by monitoring salinity level that has worked for him, this is probably a very unique situation. It may be relevant to other golf courses where similar salt levels exist, but there are too many variables to draw general conclusions. Thus, I would focus on salt levels as related to this situation and not extrapolate. What he has said may be relevant to similar situations, but it all depends on the salt levels."

I agree, and I meant to make that clear in the original post. Let me try now to explain in clear terms.

If there is a salinity problem at a site, then one will always want to minimize the salinity in the soil. If one is always trying to minimize salinity in the soil, then it is impossible to use any measure of salinity as a criterion for fertilizer application.

In a case where there is not a salinity problem at a site, it might sound reasonable to try to use salinity as an index of nutrient content in the soil. However, there are three big problems with this, and these I did describe in the original post. First, most turf managers don't want fluctuating nutrient supply; second, salinity says nothing about which nutrients are there; and third, the salinity measurements from soil moisture meters, whether EC or a salinity index, are so affected by the water content of the soil that using the salinity of non-saline soils to make decisions about fertilizer is like chasing a target that moves randomly.

I like using soil moisture meters to measure the water content in the soil. I think it is useful to assess the salinity of the soil with the meter too, if that function is available. But I don't think it is a good idea to make fertilizer decisions based on soil salinity.

I replied to Jon that "I think it is ridiculous but tried to be as polite as possible."

He wrote back:

"You, trying to be polite? Don’t lose your edge ... I think you need to clarify how unique this situation is so that others don’t try to jump on his bandwagon. His premise is flawed when applied outside of his operation."

A correspondent wrote:

"I'm hoping to get your thoughts on something I came across today.

I was discussing greens fertilising whilst at a friend's course this morning. He went on to get his new toy, the [...]. He's started to use the salinity level reading as an indicator to fertilise. So he's found a number that he's happy with that the turf looks hungry, applies a granular fertiliser and then waits for the number to drop back down to his threshold number again and repeats.

I'm not sure about this method as I've never come across it before plus I've never really looked into the salinity levels of my soils. I would just prefer to use gp and feel for when the plant needs something and adjust accordingly. But maybe he's onto something.

I would love to get your feedback on this if you're not too busy."

I replied that "I think that is a poor way to decide when to fertilize. Or what to fertilize with."

Then came a few more questions:

"Is there a particular reason why you think it's a poor way to fertilise?

If he's getting the results he desires, does that still make it poor? A reason he gave me about fertilising with a granular is [...] that by fertilising this way, he will encourage his perennial poa rather than poa annua."

First, the idea of deliberately managing soil nutrients to fluctuate up and down seems like the opposite of what most turf managers would like to accomplish.

I think most would ideally try to keep nutrient supply and growth as consistent as possible, rather than trying to cause them to fluctuate.

Second, it's changes in N that make grass grow, and then P and K and Ca and Mg and all the rest get taken up by the grass according to how much the grass is growing. So it makes sense to know the quantities of nutrients supplied, and also the quantities of the nutrients in the soil. But measuring the salinity of the soil doesn't tell which nutrients are there. It just gives the total quantity of salt.

Third, I have some concerns about the salinity number itself. The soil moisture meters that measure electrical conductivity at the same time are measuring the electrical conductivity of the water in the soil, and that measurement is strongly influenced by the amount of water in the soil. When the soil is drier, the meters give a low electrical conductivity reading, and when there is more water in the soil, even though there is no salt added, the electrical conductivity goes up.

This chart shows some measurements I made over a four day period on test plots on a golf course nursery green (pictured above). On a Sunday, I measured the soil VWC and the EC. Then I added irrigation water with 137 ppm salt, and I measured soil VWC and EC again. On Tuesday, there was a typhoon with 121 mm rain. On Wednesday, I measured the VWC and the EC again.

The EC as measured by the soil moisture meter is influenced by the water content of the soil.

One might say that is useful, because it gives some idea of the EC as the plant sees it. But if one makes that argument, then it is difficult to simultaneously make the argument that the EC is a useful criterion for determining when to supply fertilizer, because it is clear that the EC measurement is affected by the soil water content independently of the quantity of nutrients in the soil.

It is possible to adjust the EC measurement by incorporating the soil water content and the EC into a unitless measurement. The salinity index can be obtained by taking the EC, dividing it by the VWC, and multiplying by 100. This value takes into account both the EC and the amount of water in the soil at the time the EC was measured. There is not such a direct relationship between the VWC and the salinity index. But for those same data as shown in the previous chart, the salinity index also shows higher values with more VWC, even though no salt was added. In fact, after the typhoon's 121 mm of rain, one might expect leaching of nutrients, and a lower salinity index. But the opposite happened here, as shown in this chart.

And fourth, the follow-up question about if he's getting the desired results, is that still a poor way to fertilize? If he is getting the desired results, then fine, keep doing it. At some point it comes down to personal preference, because one can get good results in a lot of different ways. My preference, and what I think is a better way to determine when to supply fertilizer, involves monitoring the grass conditions, supplying N to produce the desired growth rate, and ensuring the grass is supplied with enough of each nutrient to meet the grass requirements. I expect such an approach is easier and will result in lower nutrient applications.

And about perennial Poa vs annual Poa, I'd be looking to supply a consistent amount of nutrients to the grass, rather than a fluctuating amount, because I expect the more ruderal biotypes of Poa annua would be more competitive with fluctuating nutrient supplies and with periodic granular fertilizer applications.

I was having a discussion about this last week. "I think it is a tiny amount," I said, "although sometimes I hear really large amounts when people tell me how much N comes in rain. I'll be sure to look it up." I just looked it up, and it is generally a small amount, although there are locations with more.

There are some excellent sources for N deposition data. I looked at:

• National Atmospheric Deposition Program, USA data
• Air Pollution Information System, UK data
• Oak Ridge National Laboratory Distributed Active Archive Center, global data

For an example, I downloaded data for Benton County, Oregon, and Garrett County, Maryland. Compared to the amount of N used by grass, or applied as fertilizer in a year, this isn't very much. I'd guess annual N rates would be about 10 to 15 g/m² at those locations. Adding 0.1 to 0.3 g N/m² would be less than 3% of the annual N rate.

This guide has some maps that show the N deposition by location. There are a few hotspots that may get 20 kg/ha; that could be a substantial amount of N, say 10 to 20% of the annual amount used by the grass.

I looked up data for Tower Bridge in London using the APIS site. That was an annual total of 15.7 kg N/ha. That will be a substantial amount of N for turf in that location. I'd say that would be about 20% of the amount a golf course putting green might use in London.

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:

what has been seen 2-date bi-weekly 8oz/m=significant root density increase, while 16oz/m 4 week OM reduction.

— Jerry Kershasky (@JerryKershasky) May 20, 2017

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.

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:

#ChampionBermudagrass is shallow rooting... Unless you let them breathe, keep the water moving and fertilize to the growth potential. #MLSN pic.twitter.com/P8panuf32u

— Eli Rahz (@Rahzturf) May 18, 2017

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

Roots still growing on our trial #MLSN green. 7" deep on an 80 year old push up green growing poa. @asianturfgrass @paceturf pic.twitter.com/9ykLgEBCg6

— Sue Crawford (@eastcoastsue1) October 17, 2016

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

I was in Sydney, Adelaide, and Brisbane this week to discuss the MLSN approach to soil test interpretation in four seminars organized by Living Turf.

In these seminars, I explained that the use of the MLSN guidelines is as simple as planning how many beers to buy for an upcoming party. And at this party, I want to ensure that I don't run out of beer to serve my friends.

This is a quick summary.

Another great turn out in South Australia for @asianturfgrass talk on MLSN. Photo credit to #BrandMedia pic.twitter.com/9hH1DT7XBv

— Living Turf (@LivingTurf) May 17, 2017

1: Soil test calibration involves establishing different levels of nutrients in the soil, growing a grass in those soils, and then evaluating the grass response to different levels of that nutrient. It quickly becomes apparent that these calibrations will be specific to the soil type, grass variety, and climate in which the calibration is done. Doug Soldat called these tests "expensive and time consuming." On a global scale, the word I use to describe this is impossible.

2: Because doing such extensive calibration is impossible, the conventional turfgrass guidelines were developed by adjusting the ranges from agricultural crops and soils:

"Traditionally, ranges for various nutrients are based on the past 60 years of fertility studies, particularly on forages, agronomic and horticultural crops, with adjustments made to fit perennial turfgrasses based on studies and the judgment of experienced university turfgrass scientists."

In addition to that, the conventional guidelines have in some cases been set deliberately high. That's not because grass performance would be improved by more nutrients, but because "the cost of fertilization was not considered of primary importance for turf." And that quote is right from the textbook.

3: The minimum levels for sustainable nutrition (MLSN) guidelines for interpreting soil tests take a different approach by focusing on the way turf is managed in the modern era, and considering grasses and the soil conditions used for high performance turfgrass today.

4: Use of the MLSN approach involves making an estimate of 100% of the nutrients that the grass can use, and increasing that by an additional amount to keep as reserve in the soil. One then compares the sum of the use estimate and the reserve quantity to the amount actually present, and the result of that comparison is the minimum fertilizer recommendation.

You can scroll through the slides below, or view or download them here.

After my seminar about MLSN, Daryl Sellar showed a demonstration of the TurfKeeper system. One can read about it at the website, and how it "becomes the home of all turf management planning, actions, and facility history." It starts with a job board and goes from there, with the tasks, costs, product usage, and application records all linked in a way that impresses me every time I see how TurfKeeper is used. I was recently listening to a podcast about turfgrass innovation. Dave Wilber and Kevin Hicks discussed the direction of the industry, and Kevin mentioned that there is a lot of data out there, and a lot of systems that do a good job of handling one aspect of the data. TurfKeeper puts it all together in a way that few others do.

The MLSN approach is suitable for any grass, soil, and use, because it involves both a site specific estimate of nutrient use plus a reserve amount to keep in the soil. I enjoyed seeing a range of turfgrass sites and grasses on this trip, and discussing with so many turfgrass managers the practical use of MLSN to interpret soil tests in those conditions.

That's kikuyugrass at Eagle Farm race course in Brisbane. For a good story about something that happened at Eagle Farm in 1984, read about Fine Cotton.

This is Legend green couch (bermudagrass) overseeded with perennial ryegrass at Suncorp Stadium.

I taught two seminars yesterday at the Philippine Golf Course Management conference. The first was about irrigation water requirement. The slides are here, and I made this Shiny app with data from 2013 through 2016 for Manila, Cebu, and Baguio.

In the second presentation I spoke about MLSN after 5 years. I explained what soil test interpretation is, why the MLSN guidelines were developed, and explained how they work.

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.

Taking this year's samples. Still no P or Ca applied for 4 years... or Carbon. #MLSN #keepitsimple pic.twitter.com/rdG4BEjlGO

— Andrew McDaniel (@drumcturf) April 12, 2017

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 Fukuoka.

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:

• Misunderstanding the MLSN guidelines
• MLSN webinar on Turfnet
• Preventing nutrient deficiencies