Soil

Preventing nutrient deficiencies

Clippings2

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.

Selection_123

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:

Bent_no_core


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.

Triple14_31july

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.

Particle

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.

NoBurn1

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.

NoburnHi

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

Selection_094

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.

Korai7

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.

Fuji16

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."

Selection_081

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


A little more data to support an anecdote

Yesterday I wrote about soil organic matter decreasing over a 3 year period, even though the greens had only been cored twice in that time, and sand topdressing amounts had been reduced each year.

201305
17th green after coring in May 2013

When I think about reducing organic matter, I usually think of removal or dilution. Removal would be through coring or scarification; dilution would be by mixing sand with the organic matter.

Cored_dressed
12th green after 12 mm core aerification and topdressing in May 2013

But in this case, I think the organic matter in the soil is going down because the organic matter production is less than the organic matter decomposition. The reason I think this is simple. There hasn't been much removal or dilution of organic matter in the past 3 years, but the organic matter has still gone down.

2013_mow_14
The 14th green in August 2013

In the comments to yesterday's post, there was some discussion of layering if sand was not applied often enough. I agree that undesirable layering might occur, but only if the grass was producing organic matter faster than it was decomposing.

To put this into context, I added up the volume of clippings from the greens in 2015, to give some idea of the growth rate at which the maintenance work described yesterday has led to a decrease in soil organic matter.

Green_yield

Add that up for the year and it is 270 L/100 m2. Measurements of the fresh weight of clippings on these greens give 0.3165 kg for each liter of clippings, so that is 85 kg of fresh clippings per 100 m2. I expect these clippings are about 70% water and 30% dry matter, so I've estimated the dry weight of the clippings at 26 kg/100 m2.

That gives three estimates of how much the grass is growing at this location. Those numbers might be useful if you'd like to compare the growth of grass where you are.

As an aside, these types of calculations are how I estimate nutrient harvest. If you've been to one of my seminars about how to use the MLSN guidelines, I will have described that the use of the guidelines involves taking the amount the grass will use (I'll call that a), adding that to the amount I want to make sure remains in the soil, which is the MLSN guideline (I'll call that b). These values a and b, together, are the amount of an element we want to be sure is present. a + b represent the amount we want to have. The amount we actually have is measured by the soil test, and I call that c. It follows that the amount of an element required as fertilizer is the amount we want to have, minus the amount we do have, represented in an equation as a + b - c.