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17 essential nutrients?

"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.

Books

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:

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.


"Already proving to be more valuable than I originally expected"

2017-05-23 13.23.54

When I read Jason Haines' interesting post about clipping yield, soil mineralization, and disease rates and came to the part where he said measuring all the greens was more valuable than he expected, I was glad to read that. I wanted to say "I told you so," because this is a number that I think is really useful. And I hadn't thought of the disease connection and being able to notice that, but I do know that golf course superintendents will find ways that I haven't thought of to make use of growth data. Because managing the growth rate of the grass is what it all boils down to. I've written about this in the Short Grammar of Greenkeeping. And it makes sense to me, when the clippings are collected anyway, why not take note of how many there are?

Chris Tritabaugh has a thread about this, asking what about the fertilizer that wasn't applied? And he finds, if I understand correctly, that monitoring the clippings gives some confidence that more N is or is not required at a given time.

Which is where I decide to jump in here with two quick comments. First, yesterday I had the great pleasure of writing about fertility. Now I want to mention programs. Specifically, fertility programs. I don't think program is the right word to use when considering the nutrient supply to turf.

Program means a plan of activities, or a sequence of operations that can be set to happen automatically. But with turfgrass, one can assess, as Chris wrote, "the nutrients we haven't applied" by measuring how much the grass is growing. That is, the grass is likely producing some growth in response to fertilizer applied in the past (see this for more) and one expects there is some growth related to mineralized N too.

Let's say one wants to have a flexible fertilizer system. FFS. Has a nice ring to it. Measuring the growth allows one to adjust the nutrient supply based on the grass response. Whatever one wants to call it, I think turf response will almost certainly be better, and fewer inputs will be required, if the N rate changes at almost every nutrient application. This is what the temperature-based growth potential method is based on, to set an upper limit of N supply at any time, given the weather, and then that predicted amount to supply is adjusted based on the actual grass response.

Now my second point, which is more about the utility of clipping volume. Or about mineralized N. One can expect a soil with a 10 cm rootzone depth and 1% organic matter to release about 2 g N/m2 in a year. And a soil with 2% OM may release about 4 g N/m2. For creeping bentgrass maintained at relatively low N, I expect that will produce from 50 to 100 g dried clippings per m2. And based on the relationship between clipping volume and dry weight for bentgrass, I expect that will work out to a fresh clipping harvest of 80 to 160 L/100 m2.

That is, one can predict how much extra the grass may grow after one knows the organic matter in the soil. I expect this makes sense to anyone who has put a number to the clippings mown off the putting greens, and is gibberish to everyone else. But the approach of working with quantities of nutrients in the soil, quantities of nutrients harvested, and quantities of nutrients supplied as fertilizer, allows one to get really precise, and really efficient, and supplying just what the grass requires.

And the implications are that one gets better grass conditions, one does so with less work, one has more control of the grass conditions, and there is potentially less coring, less topdressing, less disruption of surfaces, less Poa annua invasion, etc.


Tonight's reading

Books

I saw a video today with the question "what is your favorite fertility practice?" That segment starts at the 2:00 mark.

Then on Twitter I saw some comments about how funny the answers to that question were. I had a laugh because the answers are correct, but it is the question that misuses the word.

Selection_029

I don't expect the turf industry will change its jargon on this. But if one misuses the word fertility in conversations with the general public, it should not be a surprise if the responses are about fertility.


"Don't try to jump on his bandwagon"

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.

DSC_7285

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."


6.8 cm per month

A few years ago I wrote about how everyone knows zoysia grows slower than bermuda, except when it doesn't. In particular, I was discussing the growth of the nuwan noi variety of manilagrass (Zoysia matrella) in tropical Southeast Asia.

One of the examples I used in that post was the expansion rate for patches of nuwan noi in the bermudagrass fairways at the Santiburi Samui Country Club. I was back at Samui this week, and I went to the 18th hole to check the nuwan noi.

18samui

Just around the dogleg, and down the hill near the landing area, there is a large patch of nuwan noi that has overgrown the bermuda.

Nuwan_noi_18_samui

I paced it off, and the diameter of that particular patch is now 17 meters. If that started as a single plant in January 2007, and has now grown 8.5 meters in every direction, then the expansion is 850 cm in 125 months, or 6.8 cm per month.

This approximate rate keeps coming up in a number of measurements I've made. I have estimated the expansion at 7 to 8 cm per month. And in pot experiments, I get a similar rate too. For example, planting nuwan noi stolons at a rate of 1,500 nodes per square meter gives 1,500 nodes in 10,000 cm2. If each node occupies 1 cm2 at the start of the month, and then the coverage goes from 1,500 to 10,000 cm2 by the end of the month, that's an expansion rate of 6.7 cm2 for each plant in a month.

Why does this matter? Because I've hypothesized that the most sustainable grass for a given location is the one that has the most growth per unit of N and per unit of H2O applied.


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

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.

Salinity_spoon_feed

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.

DSC_4007

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.

EcPlot

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.

SalIndex

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.


Turfgrass roundup: May 2017

Billy Crow asks how do I know if I have a nematode problem?

MacKenzie's fundamental principle of greenkeeping.

Paul Jansen with an amazing video of greenkeeping in Myanmar:

Bill Kreuser wrote about PGR over-regulation on golf green collars.

See how irrigation requirement changes with daily soil water balance in the Philippines.

How can a location with more rain also require more irrigation?

Doug Soldat with more surprising photos, this time of dandelions:

Brad Revill reports on eight months of MLSN.

My 2017 workflow.

Kreuser with more PGR info:

Jason Haines thinks we can do better than organic.

Four seminars about soil test interpretation in Australia.

Is this the best backdrop in golf?

Sue Crawford with an update from the MLSN green.

The two green system in Japan isn't always about summer and winter greens.

Are you subscribed to the ATC updates mailing list? Or the MLSN newsletter list?

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.


How much N is in rain and snow?

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.

Rainfall_baguio

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

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.

Annual_N_deposition

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.


Of turf, roots, and fertilizer

I'd like to make three points.

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

Itoshima

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.

Cavite

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.

Sep2011_roots

GreenSep

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.

Sterf_n_roots

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.