Viridescent - the Asian Turfgrass Center blog

Turfgrass Notes From Korea

I was at Korea last week, where I visited six different golf clubs. Two were 18 hole facilities, one of which is under construction, one has 9 holes and is open 24 hours a day for half the year, two have 36 holes, and one has 72 holes.

That is Sky72 Golf Club, adjacent to Seoul's Incheon Airport, and as is typical of many courses in Korea, the course is lighted so that rounds can begin before sunrise and continue into the middle of the night. Two of the courses at Sky72 do well over 100,000 rounds per year, and that amount of traffic brings with it certain challenges.

There is of course the challenge of just getting the maintenance work done, but also the wear from all the traffic is severe. This is especially a challenge when zoysiagrass (Zoysia japonica) is used, as it so often is because of the climate, because there are less than six months of growth for zoysia in Korea.

At the beginning of spring, we can see in the photo above that the creeping bentgrass green has excellent grass coverage, but the zoysiagrass surround at the back of the green has been worn completely away through traffic during the winter. And the traffic makes for some unusual maintenance on bentgrass greens, where the hole location is changed multiple times per day. This is usually about every 80 to 100 players, or up to six times a day, I was told, at courses such as Korea Public GC, which hosts about 110,000 annual rounds and is open 24 hours a day from May to November. 

Greens of course require relatively high rates of nitrogen when they receive so much traffic. I've written extensively about the growth potential and how it can be used to predict nitrogen requirements. Calculating the cool-season growth potential (GP) for Seoul and estimating a monthly nitrogen use of 3.5 g N/m² when the GP is 1, we get an estimated annual use of 18.1 g N/m². But the busy courses are using, generally, 30 to 40 g N/m², to achieve the necessary growth rates to recover from traffic of more than 100,000 golfers each year.

During construction, it is customary to plant zoysia using stolons embedded in biodegradable nets that are rolled out across the fairways. After just visiting sod farms in the United States and finding that zoysia sod was selling for just over $3/m², it was interesting to note that these zoysia rolls in Korea are the same price, and the installed price, including a layer of sand topdressing, is close to $5/m². Once the rainy season and the hot weather of summer comes, this grass will fill in rapidly, and the fairway pictured above will be ready for a soft opening by October.

I saw cool technology too. At Golfzon County Sunwoon, I played 18 holes, the caddy kept our score on a tablet computer and recorded the number of putts for each hole, and she also took photos of our group on the course. When I returned to the clubhouse, I simply entered my locker number into a kiosk, and the scorecard was printed with a photo from our round, the hole by hole score, and the number of putts I had taken. It looks like I've got some room for improvement!

But that could be checked too, for there were two holes on which a video camera recorded my tee shot, archiving the swings on a website for my viewing at a later date as a record of the round, and immediately viewable on the in-cart tablet computer through the on course WiFi network. There is really some cool technology involved with these systems, and it is something that made my round of golf more fun than it otherwise might have been. 

Related articles

Turfgrass Nutrient Requirements and Fertilizer Choice

Using Waterfall Charts to Look at Soil Nutrient Levels: potassium as an example

How Much Potassium Does Grass Require?

Turfgrass Management on a Different Scale

Waterfall Chart of Putting Green Calcium Levels

Waterfall chart of potassium (K) on a golf course putting green shows why K is often required as fertilizer; the grass uses enough K in one year to drop the soil level below the MLSN guideline

A waterfall chart can be used to represent nutrient availability and use in turfgrass. This has been explained in case studies of a desirable element that is often added as fertilizer, potassium, and in the case of a less desirable element in turfgrass soils, sodium.

Potassium is often required as fertilizer because the grass uses more potassium than is available. The situation for calcium is quite different. The amount of calcium available in the soil is almost always much more than the grass requires.

This waterfall chart for calcium takes a look at the calcium in the soil and shows the various additions and subtractions of calcium over the course of a year.

Here is an explanation of these data.

1. A blue horizontal line is drawn at 360 ppm. That is the MLSN guideline for calcium, meaning we want to keep soil calcium at or above 360 ppm, and when we do that, we have a high level of confidence that turfgrass will be supplied with ample calcium.
2. The initial soil test level of 519 ppm is a typical level for sand rootzones. This is based on the median value of 100 soil samples taken from sand rootzones in five countries of Southeast Asia.
3. Annual plant uptake is expected to decrease the amount of calcium in the soil by 27 ppm. This is based on an estimated annual harvest of 900 grams dry matter per square meter, with an average leaf tissue calcium content of 0.45%. This is typical of bermudagrass turf with a twelve month growing season. Use of calcium by cool-season grasses in a temperate climate would be about half of the amount shown here.
4. No calcium is applied as fertilizer because it is not necessary. The amount in the soil is much higher than the MLSN guideline.
5. I estimate an addition of 80 ppm calcium to the soil through irrigation water. This is based on an average calcium concentration in the irrigation water of 20 ppm, and an annual irrigation amount of 600 L/m². This is a conservative estimate of irrigation application at Bangkok based on 150 days of irrigation at 4 mm per day. Note that the amount added by the irrigation water in this conservative case is three times the amount of calcium actually used by the grass.
6. I estimate a leaching loss of 67 ppm. Normally calcium won't leach. But in this case it absolutely has to. Why? Because the soil cation exchange capacity (CEC) does not change. The exchange sites in the soil already have cations reversibly adsorbed to them at the time the irrigation water is applied. So some of the calcium added through irrigation must leach. There is no place for it to remain in the soil.
7. Taking the initial amount of 519 ppm in the soil, subtracting the amounts used by the grass and lost by leaching, and accounting for the amount of calcium added in the irrigation water, we are left with 505 ppm calcium in the soil after one year. This is still well above the MLSN guideline for calcium and this demonstrates why none is required as fertilizer. 

For more information about calcium for turfgrass, see:

Nutrient profile: Calcium by Doug Soldat

How much calcium does turfgrass require?

Calcium deficiency in turfgrass, an imaginary problem?

Supplemental calcium applications to creeping bentgrass established on calcareous sand by St. John et al.

Related articles

Using Waterfall Charts to Look at Soil Nutrient Levels: potassium as an example

Waterfall Chart of Putting Green Sodium Levels

How Much Potassium Does Grass Require?

Turfgrass Nutrient Requirements and Fertilizer Choice

The Unambiguity of Nutrient Availability Indices

I've been asked a question about nutrient elements being "locked up" in the soil and if I could explain that. This question is in some way related to these posts about soil testing and nutrient requirements:

• How much potassium does grass require?
• How much phosphorus does grass require?
• How much calcium does turfgrass require?
• Calcium deficiency in turfgrass, an imaginary problem?
• Turfgrass nutrient requirements and fertilizer choice
• Sand, sodium, and soil structure
• A fertilizer miscellany: cost, phosphite, and nutritionism
• PACE Turf and the minimum levels for sustainable nutrition (MLSN) guidelines

In those posts, I have not used the terms "locked up" or "tied up" to refer to nutrients in the soil that are unavailable for plant uptake. Those terms should not be used by professional turfgrass managers because they are ambiguous and do not give the mechanism by which the nutrients are supposedly unavailable.

If we would say that some of the phosphorus (P) applied as fertilizer becomes "locked up" in the soil, what does that really mean? Does it mean the P will be forever unavailable for plant uptake? Does it mean the P is temporarily unavailable? Does it mean that all the soil P is at risk of being unavailable? Should we use a liquid fertilizer instead, to avoid this ambiguous "lock up" in the soil? And what about calcium (Ca) in a high pH soil, is it "locked up" in the form of calcium carbonate? The questions go on and on, but cannot be answered clearly because of vague terminology. It is often the case that this ambiguous terminology goes together with dubious chemical assumptions.

We avoid these problems by using nutrient availability indices, of which the MLSN guidelines are an example. A nutrient availability index does not try to say that a certain pool of measured nutrient are all of that element available. It is simply a number that, if it has been carefully calibrated with turfgrass response or turfgrass performance, can be used to determine the probability of a plant response to additional applications of that nutrient. 

In the soil, there are various forms (pools) of the nutrient elements. With potassium (K) for example, there will be some in soil solution, some on cation exchange sites, some in what is termed non-exchangeable forms, some in the soil particles (structural K), and some, perhaps, in undissolved or unreleased fertilizer granules, and a small amount in soil organic matter. But an availability index for K does not need or attempt to assess all of this. In the case of the Mehlich 3 extraction for K, we would be extracting from the soil almost all of the soluble and exchangeable K and a small portion of the non-exchangeable K and none of the structural K. But that index is useful, because after many experiments and calibration and study, we are confident that a value of 35 ppm K is sufficient for excellent turfgrass performance. 

If the index is less than 35 ppm, we would expect a positive response to added K. If the index is above 35 ppm, we do not expect a response to added K. Availability indices such as the MLSN guidelines are unambiguous and already incorporate the "locked up" nutrients. Not all nutrients in the soil are available for plant uptake. But they don't have to be. We just need to know if there are enough, or not enough. The MLSN guidelines provide an unambiguous answer.

How Much Potassium Does Grass Require?

In last week's TurfChat, in which we discussed the relationship between soil nutrient levels and weeds, I mentioned that recommendations for soil potassium (K) tend to be unreasonably high. We can see that particular section of the discussion beginning at the 31:55 time of the TurfChat video:

The most accurate, and consequently, the most useful, guidelines for interpreting soil nutrient levels for turfgrass are the minimum level for sustainable nutrition (MLSN) guidelines. These guidelines have been specifically developed for turfgrass with special consideration of the sandy soils that are commonly used for high traffic turfgrass areas.

The MLSN guideline for K is 35 ppm.

I mentioned in the video that conventional guidelines are much higher, ranging typically from the conventional PACE Turf guideline of 110 ppm to the Penn State University target of at least 180 ppm. But there is no reason for soil K to be so high, nor can we expect most turfgrass soils to hold that much K.

When we look at the results of relevant research papers, we see that the recommendations developed after the completion of carefully controlled experiments give guideline levels very close to the MLSN guideline. Here are just a selection of typical results.

Ebdon et al., 2013: less than 50 ppm, Morgan extraction, "there were no observed changes in shoot and root growth in response to K fertilization even at low soil test K levels"

Paul, 1981: 20 ppm, ammonium acetate extraction, "beyond 20 ppm, there is no response to K fertilization"

Sartain, 2002, 30 ppm, Mehlich 1 extraction, "the critical Mehlich-1 extractable level of soil K appeared to be near 30 ppm"

Woods et al., 2006, less than 50 ppm, Mehlich 3, Morgan, and ammonium acetate extractions, "the current target ranges of extractable K in sand rootzones promote K fertilizer application that may be detrimental to turfgrass performance. Recommended levels of soil K should be reevaluated to avoid gratuitous use of K fertilizers"

The MLSN guidelines have done just that, and the methodology used to develop the MLSN guidelines results in a recommendation in line with those developed through controlled field research.

There are a number of implications resulting from using outdated and inaccurate K guidelines. It is obviously a waste of money to apply unnecessary potassium. There is wasted thought in trying to solve an imaginary problem. Application of K will reduce, unnaturally, and possibly to the detriment of plant health, the amount of calcium and magnesium in the grass. In some situations, it is expected that addition of K will increase the number of weed species that can grow. And unnecessary applications of K may cause other unexpected problems, such as increased disease.

Nutrient Supply and Plant Species Diversity

On March 28 (or March 29 in Asia), Episode 23 of the Turf Diseases Turf Chat will be on the subject of Soil Nutrients and Weed Management. This promises to be an interesting discussion, led by Dr. Scott McElroy from Auburn University and hosted by Dr. Larry Stowell of PACE Turf.

It is a well-known phenomenon that application of nitrogen favors grasses and reduces species diversity (i.e. reduces the number of weedy species), while increasing the soil pH through addition of lime, and adding potassium fertilizers, as an example, can increase the prevalence of weeds. In a brief exchange on twitter last week, we discussed this, and decided to make this subject the focus of the upcoming Turf Chat.

@asianturfgrass @campbellturf @pendersuper to me the dandelion paper is typical ecology-speak. Making a big deal of something already known.

— Scott McElroy (@malherbologist) March 23, 2013

Dr. McElroy says that this phenomenon is already known, while I would argue that despite it being noticed more than 150 years ago, and the mechanisms of this worked out more recently, among turfgrass managers, there is not universal knowledge of these principles.

That was the subject of an article I wrote with Dr. Frank Rossi from Cornell University about the Park Grass Experiment and some of the results from this classic experiment, especially the noted absence of dandelions from plots to which potassium fertilizer is withheld.

For more detail about this, please read our article about Park Grass from the Green Section Record, and you can find a list of references at the end of that article for additional reading. Of particular interest may be this one, by Silvertown et al., The Park Grass Experiment 1856-2006: its contribution to ecology.

10 Years Ago Today, a Startling Observation About Potassium and Snow Mold

Ten years ago today, I was a graduate student at Cornell University, and after the snow had melted off of the research green, I walked over to the research area to check the condition of my experiment. It was a cold day, in early spring, and I took this picture not noticing so much about the differences in snow mold incidence on the L-93 creeping bentgrass of this experiment. It was not until April (see below) that I really noticed what a huge difference there was between the different fertilizer treatments.

In the previous summer, the turf was all the same, showing no visual response to any application (or withholding) of potassium (K) fertilizer.

And in the autumn of 2002, just before the snow would fall and would cover the green for months, there was no difference at all in turf performance.

The previous summer the turf was all the same, no matter how much K was applied, and in November before the snow the turf was all the same also. There was more K in the leaves where K had been applied, and there was more K in the soil, where K had been applied, but the visual appearance of the turf was all the same. 

I did not apply any fungicides to this experimental area in the autumn of 2002. 

In the spring of 2003, when the snow melted, I expected that all the plots would be the same, as they were in November before the snow fell.

So it was a startling observation to find that there was more snow mold damage on the plots to which K had been applied in the previous year. The plots with more available K in the soil, and the plots with more K in the leaves, had more damage from snow mold than did the plots to which no K was applied at all the previous year!

I wrote about this in my article summarizing this experiment. Continuing research by Moody and Rossi has shed more light on just what it is that may cause this phenomenon. 

Application of K when it is not required may cause unexpected problems. By using the MLSN guidelines to determine when K fertilizer is required, one can have confidence that unnecessary fertilizer applications are being avoided.

Waterfall Chart of Putting Green Sodium Levels

I have decscribed how a waterfall chart can be used to show the nutrients that enter and leave a system, using potassium as an example. In that example, I did not show any input of potassium from irrigation water or rainfall, because I made the assumption that those inputs would be negligible. David Kuypers, the Golf Course & Grounds Superintendent at Cutten Fields in Guelph, Ontario, asked what would happen with sodium (Na) added through irrigation water:

@asianturfgrass Any need to account for an input through irrigation water? Average here is 110ppm for Na. Impact reflected in soil test?

— David Kuypers (@gcscuttenfields) March 19, 2013

That is an excellent question, and this chart for Na shows what may happen with that element. Let's look at a few components of this waterfall chart.

1. The horizontal blue line at 110 ppm marks the MLSN guideline for Na. Unlike the 35 ppm level for K, which is a minimum guideline, this 110 ppm maximum guideline for Na is related to increased chance of rapid blight disease at soil Na concentrations above 110 ppm.
2. I assume that we start with a Mehlich 3 extractable Na of 75 ppm. The annual plant uptake of Na is minimal for cool-season grass and I estimate it as being equivalent to a decrease in soil Na of 5 ppm. 
3. I assume no Na is added as fertilizer.
4. David said that his irrigation water has an average Na concentration of 110 ppm. That means for each liter of water, there are 110 mg of Na. If he adds 205 mm of irrigation water to the greens over the course of the season, that is equivalent to 205 L of water for each square meter. If we assume that the 22,550 mg of Na contained in those 205 L of irrigation water are distributed throughout the top 10 cm of the rootzone, and that the bulk density of the rootzone is 1.5 g/cm³, then that amount of Na will increase the Na in the system by 150 ppm.
5. With this depiction on the waterfall chart, we can see that the amount of Na expected to be added with this much irrigation is twice the amount of Na that was in the soil at the start of the year. And we can make some comparison of the magnitude of each input and loss of Na from the system.
6. However, sometimes there will be thunderstorms or other heavy rain events that will cause some leaching of that Na. Most of that Na will be remaining in soil solution; it won't be extensively held on cation exchange sites which would make it resistant to leaching. And if rain doesn't come, I assume that David will sometimes apply extra irrigation water to induce leaching of the Na. I assume that 130 ppm of the Na will be lost by leaching.
7. With these assumptions, that leaves us at the end of the year with 90 ppm of Na in the soil, still below the 110 ppm MLSN guideline. And if we would go through the fall, and through the winter, we would expect no irrigation water to be applied, and some leaching to occur, and by the start of the next irrigation season, the Na would be reduced even more. In an arid climate, the Na would be expected to increase and increase, but in a humid climate, one in which precipitation exceeds evapotranspiration, most of the applied Na is expected to leach.
8. We can see that if no leaching occurs, the addition of Na through irrigation will increase soil Na above the MLSN guideline of 110 ppm.

For more about maintaining soil Na below 110 ppm, see this document from PACE Turf.

Using Waterfall Charts to Look at Soil Nutrient Levels: potassium as an example

I have recently described a method that can be used to estimate nutrient requirements for any turfgrass, grown at any location. This method makes use of the temperature-based growth potential and the minimum levels for sustainable nutrition (MLSN) guidelines.

This method makes a few basic assumptions about turfgrass management.

1. The soil can hold a fixed amount of nutrients; it cannot hold an unlimited amount.
2. The plant takes up a limited amount of nutrients; the plant does not take up an unlimited amount.
3. Application of more nutrients than the soil can hold, or than the plant can take up, provides no benefit to the grass, nor to the soil, and is in fact inherently wasteful.

This is essentially a mass balance approach, in which we consider the rootzone and the turfgrass as a system and we account for the nutrients that enter and leave that system. We can use a waterfall chart to visualize the individual and cumulative effects of the nutrient addition and the nutrient loss from our turfgrass and rootzone system.

This type of chart is described on Wikipedia as:

The waterfall chart is normally used for understanding how an initial value is affected by a series of intermediate positive or negative values. Usually the initial and the final values are represented by whole columns, while the intermediate values are denoted by floating columns. The columns are color-coded for distinguishing between positive and negative values.

Let's look at potassium (K) as an example, developing the chart step-by-step. I first make a frame for the chart. I've labeled the y-axis with K expressed in units of ppm (mg/kg).

Next, I draw a horizontal line, in blue. 

This line is at 35 ppm, which is the MLSN guideline level for K. What the MLSN guideline means, in simple terms, is that we have a high level of confidence that turf will perform well and will have access to ample amounts of an element, as long as the soil level remains at or above the MLSN guideline. For K, we are confident that the turf will perform well and will have access to ample K when the soil K, as measured by the Mehlich 3 soil test extractant, is at or above 35 ppm.

Then I add on a column to represent the amount of K actually in the soil, as determined by a soil nutrient analysis. In this example case, the soil test value is 70 ppm. This is a typical value for Mehlich 3 K in a sand rootzone. Note that this is more than the 35 ppm MLSN guideline, and we consider this soil test level as our starting point. Any positive amount of an element, or an addition of that element to the system, I will represent with a black color. Any loss of an element from the system will be represented in red.

Next I add a column for annual plant uptake. This is based on the assumption that leaf clippings will be collected and removed from the system. This removes whatever elements are in the leaf clippings, including K. We can note a few things here:

1. The color of the "Annual Plant Uptake" bar is red, meaning this is a loss of K from the system.
2. ­­­‒54 is shown at the bottom of the bar, which indicates 54 ppm of K is estimated to be lost from this system by annual plant uptake.
3. 54 ppm is equivalent to 8 g/m² (or 1.6 lb./1000 ft²) when expressed on a mass per area basis, and this assumes average rootzone depth of 10 cm and a soil bulk density of 1.5 g/cm³.
4. This amount of annual uptake and removal from the system is what we would expect when average leaf K content on a dry matter basis is 2% and when the annual dry matter clipping harvest is 400 g/m². This would be typical of creeping bentgrass greens in a climate such as Tokyo or New York.
5. Notice that if we simply combine the soil test level at the start of the season, which is 70 ppm, and then account for the annual plant uptake, wich is estimated to be 54 ppm, then we drop the amount of K in the system to less than the MLSN guideline, all the way down to 16 ppm.

But we don't want the K to drop below the MLSN guideline. To prevent this, some K will be applied as fertilizer. Let's look at the chart now that the "Fertilizer Applied" column has been added.

1. The "Fertilizer Applied" column is in black, indicating that this is an addition of K to the system.
2. The amount added, 67 ppm, is equivalent to 10 g/m² (or 2 lbs/1000 ft²). This assumes the K is added to the top 10 cm of the rootzone and that the soil has a bulk density of 1.5 g/cm³.
3. Notice that the Soil Test column has a length of 70, the Annual Plant Uptake column has a length of 54, and the Fertilizer Applied column has a length of 67. This is useful in comparing the magnitude of the amounts in the system. The amount of Fertilizer Applied is greater than the amount of Annual Plant Uptake, and the Fertilizer Applied is similar in amount to the level of K in the Soil Test at the beginning of the season.
4. The amount of K in the system, because of the K addition through fertilizer, has now increased to above the MLSN guideline of 35 ppm.

To complete the chart, I add a final column, to show the amount of K "Remaining in Soil". This column has a length of 83, showing that there is 83 ppm of K in the system. This is 70 minus 54 plus 67. And it indicates that when we have a starting level of 70 ppm of K in the soil, with a harvest through plant uptake of 54 ppm, and a fertilizer addition of 67 ppm, then we expect to have 83 ppm of K remaining in the system (in the soil) and that this level is well above the MLSN guideline.

I find this to be an interesting graphical approach to depicting soil nutrient levels and their relationship to the MLSN guidelines. If we would look at nitrogen, or calcium, or magnesium, or phosphorus, using this approach, we can understand more clearly how the amount in the soil is related to the plant uptake, and how that helps to determine the annual nutrient requirement as fertilizer.

Turfgrass Nutrient Requirements and Fertilizer Choice

I made two presentations this week at the Sustainable Turfgrass Management in Asia conference. The slides and supplemental handouts from these presentations are available for download with links provided below.

The handouts for each talk are the most useful of these documents. Although the title of the first presentation is Nutrient Requirements of Tropical Turfgrass, the handout outlines a method that can be applied to any grass, at any location, to determine nutrient requirements.

This presentation makes use of the temperature-based growth potential (GP) of PACE Turf. After my talk, I was asked if there is a web-based service available for determining GP at one's location. There is not, but PACE Turf, in their IPM planning tools, provide Climate Appraisal Forms that have the growth potential equation embedded and are an easy way to introduce oneself to these calculations.

The second presentation is entitled What Fertilizer Should I Use? The accompanying handout explains how expected nutrient use of the grass can be compared to soil nutrient levels to determine exactly how much, and of which elements, should be applied in order to keep the nutrient availability at or above the minimum levels for sustainable nutrition (MLSN) guidelines.

Handout: Nutrient Requirements of Tropical Turfgrass, 5 page PDF

Handout: What Fertilizer Should I Use, 4 page PDF

Turfgrass Fertilizers: an exemplary fact sheet

This fact sheet, Selected Fertilizers Used in Turfgrass Fertilization by Dr. Sartain and Dr. Kruse from the University of Florida, is only 12 pages long but is packed with useful information about the primary sources of turfgrass nutrients.

Covering the major fertilizers from ammonium sulfate to urea, potassium chloride to Polyon, this document serves as a reference and a review of the various properties of these fertilizer products. This is an excellent guide to the main sources of nitrogen, phosphorus, and potassium applied to turfgrass, along with an overview of some of the different controlled-release nitrogen sources.

I shared this on twitter last week and it received an unusually high number of retweets and favorites, so I'm sharing this again here. It is a good document to have on one's desk or computer.

This is an exemplary fact sheet about turfgrass fertilizers @jkkruse edis.ifas.ufl.edu/pdffiles/SS/SS…

— Micah Woods (@asianturfgrass) February 1, 2013