Mineral nutrients in the leaves vs. those in the soil

Last year I shared an elemental cartogram of relative mineral nutrient amounts in turfgrass leaves. An elemental cartogram is a periodic table of the elements with the area of each element modified by a theme, and in this chart the area is modified by the amount of mineral nutrients.


One thing I notice on the cartogram of mineral nutrients in bentgrass leaves is this: where are the micronutrients? We can see the macronutrients clearly: N, K, and P. Then the secondary nutrients: Ca, Mg, and S. But the micronutrients are in the leaves in such small concentrations that they don't register on this cartogram, in which their quantity is compared to those of the macronutrients and secondary nutrients.

The quantity of an element required as fertilizer is the difference between the amount the grass requires and the amount present. I wondered how the cartogram of elements in leaves would compare to a cartogram of nutrients in the soil. For that, I looked up the Global Soil Survey data, and generated a cartogram using the median values of the elements measured in the Global Soil Survey.

Selection_044This looks a bit different, and is illustrative of a couple things related to fertilizer. First, N is low in the soil, but the plant uses a lot of N. Comparing the two charts makes it clear why N is applied as fertilizer to most turfgrass sites. Second, K is relatively large in the cartogram for leaves, and much smaller in the cartogram for soil. Because the plant demand for K is relatively high, compared to the amount in the soil, K is often required as fertilizer. Third, Ca and Mg and some micronutrients are much higher in the soil than they are in the leaves, providing an illustration of why these elements are rarely required as fertilizer.

Waterfall charts provide a more explicit example of these calculations, but the cartograms are kind of fun to look at.

How soil K changes over time

These data show what happens to potassium (K) in the soil when different rates of K fertilizer are applied. Over two years, I made 25 applications of K to a plot of L-93 creeping bentgrass in Ithaca, New York. In 2002, I made 13 applications, and in 2003, I made 12 applications. K was applied at 6 different rates, and N was supplied in equal amounts to each plot.

This chart shows the starting soil test K, before any of the 25 treatments had been applied, and also the final soil test, two years after the first one, and after all those 25 fertilizer applications had been made. I'm showing data here from the 0.01 M SrCl2 soil test (that is "hundredth molar strontium chloride") because that test has high accuracy and sensitivity in sand rootzones. These data are proportional to Mehlich 3 data, but lower in this sand by about 50 ppm. So 30 ppm by 0.01 M SrCl2 would be about 80 ppm by Mehlich 3.


Before any of the treatments were applied, the soil test K was about 29 ppm. When no K was applied, the soil test K went down. When more K than N was applied, the soil test K went up.

This next chart shows those same data, with the 25 application dates when K was applied marked in green.

K2I'd like to point out that on the final date of sampling shown here -- 30 May 2004 -- it was 7 months after the final K fertilizer application of 2003. And you'll notice that there is a big difference in soil test K, with less than 20 ppm in the plots to which no K fertilizer was applied, and more than 50 ppm in the plots to which 4.6 grams of K were applied for every gram of N applied.

What about precipitation? Shouldn't heavy precipitation cause the K to leach? That's not the way it works. From the first soil test date of 4 June 2002, when the soil test K was 29 ppm, to the last date, there were 20 days during which the precipitation was greater than 25 mm. This chart adds on those dates, marked as blue asterisks. The asterisks are jittered up and down, to avoid overplotting.

K3Each of those 20 days had more than 25 mm of precipitation, for a grand total of 719 mm (28.3 inches) just on those 20 heavy precipitation days. There were 4 such days between the last K application and the soil testing on 30 May 2004. But the amount of K in the soil looks like it was controlled by the quantity of K fertilizer applied, not by the amount of precipitation.

I wrote about this in "I'd be applying potassium all the time" parts 1, 2, and 3. Adding K based on rainfall is a sure way to apply way more potassium than the grass can use or the soil can hold. For that matter, so is adding more K than N.

What is even more important than all the soil test numbers is the performance of the grass. And all the K added in this experiment, all 25 applications of K at different rates over 2 years, didn't cause any improvement in turf performance. Here, in the flagged rectangle, are those L-93 plots to which the K treatments were applied. This photo was taken on 19 August 2003.

K trial north

At the soil test levels of K in this experiment, there was enough K to meet all the grass requirements, across the range of adding no K for every 1 gram of N (a 1:0 ratio of N:K) all the way to the highest rate of 4.6 grams of K for every 1 gram of N (a 1:4.6 ratio of N:K). All the more reason not to worry about replenishing soil K after a rain.

What one should do is look at the soil test K, make sure it will stay above the MLSN guideline for K, and then don't worry about K.

Why light is more important for ultradwarf than for bent: my presentations at the Japan Turf Show

I'm giving two presentations at the Japan Turf Show in Tokyo this week. In the first one, I explain why light, by which I mean photosynthetically active radiation (PAR), is more important for ultradwarf bermudagrass than it is for creeping bentgrass. I use data from Tokyo and from Watkinsville, Georgia, to demonstrate this and to point out the difference in PAR between Japan and the region of the USA with similar temperatures.

The slides for this presentation about light are available in English and in Japanese.

In a second presentation, I talk about management of ultradwarf bermudagrass greens, explaining how this species performs compared to creeping bentgrass in Japan, and how it should be managed.

The slides for this presentation about ultradwarf management are available in English and in Japanese.

Bentgrass in hot and not so hot places

Creeping bentgrass is a cool-season grass. When temperatures are hot, it doesn't perform well. I was asked if bentgrass in southern China was comparable to bentgrass in Spain. I don't think that is the right comparison. It would be more appropriate to compare southern China to Florida.

I downloaded the 2014 daily temperatures for the international airports at the cities shown in this chart, then plotted the cumulative sum of the mean temperature for the year.

SumTemperatureGuangzhou and Orlando had the same cumulative sum of temperature. Bentgrass wouldn't be a good choice in Orlando, and I don't think it is a good choice in Guangzhou either.

A better way to look at bentgrass suitability is to look at the low temperatures. If the low temperatures are too high, for too many days, bentgrass will be really difficult to manage, eventually becoming too much of a problem and one would be better off with a warm-season grass.

For 2014, here's the number of days with a low temperature greater than or equal to 22°C. I'd look at anything more than 60 days in a year above that level as being difficult for bent.

BarChartLowsThis way of evaluating the temperature fits pretty well how one expects bentgrass to perform in these locations. Perfect in Kunming, the "Spring City." Pretty good in Spain. A challenge in Shanghai summers, with some warm-season greens there also, but possible with good management. Not used in Orlando. And I wouldn't want to try it in Guangzhou.

For more about temperatures and bentgrass, see:

"I'd be applying potassium all the time": Part 3

One doesn't need to apply supplementary potassium (K) after a rain, as I wrote in part 1 of this series, because such applications will invariably lead to application of way more K than the grass can use. In part 2, I showed a calculator that makes an estimate of how much K is reasonable to apply as fertilizer, based on how much K the grass will use.

Looking at this with soil test data, these four charts show what happens to K in the soil over time.

In 2002, I applied nitrogen (N) and K every two weeks to L-93 creeping bentgrass maintained as a putting green in Ithaca, New York. I collected soil samples every eight weeks. This summarizes what happened during the summer of 2002.

At the start of the experiment, before applying any N or K, the Mehlich 3 K was 86 ppm, and the water extractable K was 8.3 ppm. I've added a horizontal line at each of those levels, to indicate what the starting level of soil K was in this experiment.

Plot1Then the treatments started, N and K every 14 days. When no K was applied, what happened? The soil K went down. That is to be expected, because the grass uses K, so when the grass is growing one expects the soil K to go down if no K fertilizer is added.

Plot2What happened when a moderate amount of K was added? Over these 16 weeks in the summer of 2002, I applied 12 g N m-2, and the K rate supplying 13 g K m-2 in that time is close to a 1:1 ratio. From June to July, the soil K went up at that rate, because that is slightly more K added as fertilizer than the grass can use. Then from July to September, the soil K in plots supplied with the 1:1 ratio went right back to where they started the summer. The reason for the decrease is discussed below.

Plot3What happens when the K applied is way more than the grass can use? The highest rate in the experiment supplied 50 g K m-2 over this time period, roughly a 1:4 ratio of N to K. And the soil test levels went up, because when one supplies a lot more K than the grass can use, that's what happens.

Plot4Why was the soil K higher in late July than in September? That is because the irrigation of this area was increased in August, and the rain + irrigation from the end of July to the time the samples were collected in September was double the evapotranspiration (ET).  From the start of the experiment until the samples were collected in late July, the rain + irrigation was just slightly higher than the ET.

The grass performance was good in all the plots, and equally good no matter if no K was applied, if a moderate rate of K was applied, or if the highest rate of K was applied.

There were six rain events with > 25 mm (> 1 inch) of rain during these 16 weeks. Adding K after rain would have accomplished nothing, other than supplying even more K than the grass would use, and supplying K that would mostly be leached out sometime in the future. By supplying the amount of K the grass uses, one can maintain a pretty stable level of soil K. Of course if the soil K is well above the MLSN guideline, then no K is needed at all, because the grass can get all the K it needs from the soil.

For more details about the experiment, see this paper from Soil Science.

A turfgrass recipe, with ingredients

Today I have two seminars at the 北海道グリーン研究会 autumn meeting. That's the Hokkaidō gurīn kenkyūkai -- the Hokkaido green research association. You can view or download the presentations and handouts at the links below.

The first presentation is called If turfgrass growth were a recipe, these are the ingredients.

There are four main factors (ingredients) that influence growth. These are temperature, water, light, and nitrogen. And one can either measure or control each of them.

Adjusting the growth rate of the grass is what greenkeeping is all about. And being able to measure and control the "ingredients" allows one to compare maintenance at one site to another, compare differences from year to year at the same site, and adjust inputs for different species. This provides a template for improvement of the turf through adjustments to the growth rate.

The second presentation is called How I would manage bentgrass greens today.

I explain how I would measure and control the ingredients of growth, and explain how I would do it differently today than I did 15 years ago when I was a greenkeeper managing bentgrass greens in Japan.

Indices of temperature and light and their relative effect on turfgrass

These values are calculated from the daily weather data in 2014 at Holly Springs, Mississippi:

  • the temperature-based growth potential for cool-season (C3) grass, labeled here as gpC3
  • the temperature-based growth potential for warm-season (C4) grass, labeled here as gpC4
  • the daily light integral (DLI) divided by the maximum possible DLI on that day, labeled here as dli_index

Each of the three values have been calculated for each day of 2014. That gives 365 values for gpC3, 365 for gpC4, and 365 for the dli_index.

These histograms, with the breakdown of what values were for these three calculations,  show why I say that variations in temperature affect growth more than variations in light.

HollyHistogramsFor the DLI index, there are few values around 0, and many above 0.75. There are about 90 days for C3, and more than 150 for C4, with a growth potential of about 0.

Is ________ an essential practice, or a waste of time?

That's the question Bill Kreuser asked about syringing to reduce the temperature of cool-season turf during periods of extreme heat stress.

He prepared this document with a nice summary of the topic. Spoiler alert: "Does syringing help? Unfortunately, the answer is most typically no."

For more about syringing and irrigation, see:

Distribution of daily light integral (DLI) at Tokyo and Watkinsville in 2014

I discussed photosynthetically active radiation during a seminar this week in Tokyo.

This slide showed the distribution of the daily light integral (DLI) in Tokyo during 2014 on days with an average temperature greater than or equal to 20°C.

I mentioned that one could make an overlay of the distribution of DLI at other locations, and that a distinctive feature of the Tokyo-area climate is that there will be more days with a low DLI than at locations with a similar temperature in the southeastern USA.

In this plot, I show the density of DLI in 2014 for Tokyo and Watkinsville.


The temperatures in these locations were similar in 2014; the mean of the mean daily temperatures was 16°C in Watkinsville and 16.8°C in Tokyo. There were 151 days in 2014 with mean daily temperature >= 20°C in Watkinsville; Tokyo had 150 such days.

For the DLI on those days, however, there is quite a difference. The median DLI for those 150 days in Tokyo was 35.8, compared to 42.1 in Watkinsville.

Seminar on the fundamentals of turfgrass maintenance

Yesterday I gave a private seminar in Tokyo on the fundamentals of turfgrass maintenance.

I spoke about how I define greenkeeping, the four factors that influence growth, some specific challenges of turf maintenance related to the climate of Japan, and the fescue playing surfaces at the recent U.S. Open at Chambers Bay.

The slides for this seminar are available in Japanese or English.