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June 2014

A Waste of Time and Money

I've been doing some research about turfgrass nutrient uptake in 2 dimensions at the soil surface (grams of an element harvested per square meter) and how that is related to soil nutrient depletion in 3 dimensions in the soil volume (grams of an element removed from the soil per unit of soil volume). As so often happens in these type of researches, I'm delighted to find that Wayne Kussow already studied this. 

The amount of nitrogen supplied to the grass controls how much biomass will be produced. That amount of biomass then determines the amount of other elements that will be used. Kussow et al. summarized this phenomenon in their Evidence, Regulation, and Consequences of Nitrogen-Driven Nutrient Demand by Turfgrass

In a paper I hadn't seen before, from 1995 in the Wisconsin Soils Report (for more from this excellent column, see here, and here), Kussow wrote about manipulating creeping bentgrass nutrition. What did he find?

By going from 2.0 to 8.0 Ib N/M/season [10 to 40 g N/m2/year], there was a substantial increase in shoot growth. This, in tum, altered the nutrient demand of the turfgrass and clipping concentrations of several nutrients changed accordingly. Without this change in nutrient demand, uptake of nutrients such as P and K remained unchanged even when the nutrients were applied.

And then this choice quote:

How many more times do I have to say that applying nutrients to turfgrass growing on soil already well supplied with the nutrients is a waste of time and money?

I'm studying this, of course, as part of further development and research related to turfgrass nutrient requirements and the MLSN guidelines. One of the innovative approaches we have taken with the MLSN guidelines is to relate the 2-dimensional harvest of nutrients to the 3-dimensial stock of nutrients in the soil. Then we account for that relationship in the resultant fertilizer recommendations. For an example of this, see the mlsn_K calculator to determine K requirement.

With the MLSN guidelines, we can optimize turfgrass performance without wasting time or money. 

The greens here have never been better: on EIQ and pest management programs

This is one of those "if I were a greenkeeper today, this is how I would do it" type of stories.

At the Bethpage maintenance facility; research here demonstrates that use of EIQ can reduce environmental impact from 33 to 85% while producing the same quality turfgrass

I was pleased to read the update from Jason Haines about his use of the EIQ (environmental impact quotient) and the results he is getting. He reports that he is ahead on cost goals, ahead on EIQ goals, and that "the greens here have never been better." That sounds like a win-win-win situation.

The EIQ Field Use Rating based on formulation and application rate allow turf managers to identify and choose products based on their predicted environmental impact. From the New York State IPM Program, which administers the EIQ:

By using the EIQ model, it becomes possible for IPM [integrated pest management] practitioners to rapidly estimate the environmental impact of different pesticides and pest management programs before they are applied, resulting in more environmentally sensitive pest management programs being implemented.

Because of the EPA pesticide registration process, there is a wealth of toxicological and environmental impact data for most pesticides that are commonly used in agricultural systems. However, these data are not readily available or organized in a manner that is usable to the IPM practitioner. Therefore, the purpose of this bulletin is to organize the published environmental impact information of pesticides into a usable form to help growers and other IPM practitioners make more environmentally sound pesticide choices.

Jennifer Grant wrote about the use of EIQ Field Use Ratings in research projects at Bethpage State Park. The results there?

Using the Environmental Impact Quotient (EIQ) as the measure, impact was reduced on progressive IPM/alternative culture greens by 33%-85% compared to the conventional pest management/conventional culture greens — almost always without a loss in quality.

The EIQ incorporates the toxicological and environmental impact data for pesticides and makes it easy for turfgrass managers to compare the products they might use, allowing them to choose the one with a lower EIQ — a lower environmental impact.

5 links: irrigation, soil moisture, syringing, and controversy


It is summer in the northern hemisphere, and that means many turf areas will require irrigation. Here are 5 links that I think provide some valuable information about how to irrigate effectively. Or at least, how to think about soil moisture and water application in an ideal situation. But be warned – these have also been among the most unpopular (or at least controversial!) posts I've made. 

The numbers don't lie. Frequent irrigation can be used to maintain lower soil moisture content than infrequent irrigation. Canopy temperatures of bentgrass are "not markedly affected by varying the volume or timing of syringing applications." And the metric system, if you are using soil moisture meters, makes it a lot easier to manage the soil moisture. 

The most common soil testing mistakes and how to avoid them

As I've mentioned, one of the regular columns I really enjoy reading is the Wisconsin Soils Report. In the May/June 2013 issue, Doug Soldat asks "How reliable is soil testing?" He pointed out some of the limitations of soil testing – they are probably more extensive than you thought – and provided some good advice about practical and effective soil testing. The focus of the article is on the most common soil testing mistakes, and how to avoid them.

You will want to read the entire article, which you can download at the link, but in the meantime here are a few relevant quotes.

On soil test extractants: "While Mehlich-3 may not be the best test for all situations, it is regarded by many as the most versatile extractant and it’s the one we have the most calibration data for here in Wisconsin, with the Bray coming in a close second."

On soil test recommendations: "Turfgrass researchers continue to improve the soil testing recommendations, but that type of research is time consuming and expensive. It is also worth noting that every time a researcher conducts one of these studies, they tend to find that the levels required are lower than what we previously thought – meaning that “low potassium” you got on your last soil test report might be optimum down the road."

On recommended nutrient guildeines: "I recommend you compare your results with PACE Turf’s Minimum Levels for Sustainable Nutrition guidelines which can be found here: ... the minimum levels published by PACE are drastically lower than many traditional soil test interpretations, and likely more accurate."

Turfgrass and textbooks: are there problems with potassium?

In 2004, I asked "Does potassium fertilizer really increase roots?" in TurfNet Monthly. The answer, pretty clearly, is No, except in the case where the added potassium eliminates a deficiency. I was asked a question about potassium at a conference, was intrigued, and went to the library to find and read a number of papers that were cited as showing that higher soil potassium levels yield increased root development and branching. After reading the papers, I came away with a completely different understanding:

An increase in roots was obtained with the first increment of potassium fertilizer that was added, but more potassium than the initial increment had either no effect or actually decreased root mass. In all of these studies, just one thing stands out: potassium deficiency inhibits root growth. One can readily deduce that a positive root response to potassium fertilizer can only be expected when initial soil potassium levels are extremely low. Application of more potassium, above and beyond that amount required to eliminate the deficiency, can actually reduce roots.

Read the full article here. I recently read a number of papers about potassium and stress tolerance, with a similar interpretation, and have developed this calculator to determine how much potassium fertilizer is required to keep the soil levels above those dangerous low levels.

Woods_potassium_roots_turfnet_nov04.pdf (page 1 of 2)

Important questions and a good discussion: MLSN guidelines, K, and stress tolerance

Last week, a turfgrass scientist wrote to me with some concerns about the MLSN guidelines. My correspondent was particularly concerned about me being too dismissive of previous research results showing a beneficial effect of adding more potassium than the grass can use. 


These were really good questions, and I took the opportunity to write a full response, which I am sharing here. The conversation touches on the development of turfgrass soil testing guidelines, peer review and journal publication, and most extensively, how we can interpret the results of potassium experiments.

Calculating potassium fertilizer requirement using the MLSN guideline


All the essential elements are important, and I don't rank any of them as more important than the others. But when it comes to risk of deficiency, potassium (K) is right at the top of the list. That is because K is used by turfgrass plants in quantities second only to nitrogen. In the case of seashore paspalum, K can be used in even greater amounts than nitrogen. A K deficiency is, in many cases, disastrous.

To prevent that, one can use the MLSN guidelines, which for K the guideline is 35 ppm, meaning one needs to keep the soil at or above 35 ppm. As long as the soil K is at or above that level, I am confident that K will be present in ample amounts for the production of high performing turfgrass surfaces. 

SpeciesBut to keep above 35 ppm, a number of factors are involved. One needs to know the grass species, the amount of N applied, which controls the growth rate and consequently the K uptake, and also the amount of K that is in the soil.

I have made this Shiny app that allows one to calculate the K requirement based on grass species, annual N rate, and soil test K.

First, choose the grass species. I've made some estimates of N:K ratios in the leaves of these species that allow us to estimate how much K the grass will use, based on the amount of nitrogen that is applied as fertilizer. 

Most cool-season grasses have a N:K ratio in the leaves of about 2:1. The big differences are bermudagrass (3:2) and seashore paspalum (1:1) , which tend to have relatively lower amounts of N and higher proportions of K.

SelectThen, use the slider for soil test K to select the amount of K in the soil, as determined by a recent soil test. Note that the MLSN guidelines were developed using data from the Mehlich 3 soil test extractant; if you use a different extractant, proceed with caution. You might estimate how this value would be on a Mehlich 3 test, or submit a set of 3 samples for the MLSN project Global Soil Survey, which will get you the required Mehlich 3 data.

Next, choose how much N you intend to apply in the next 12 months. I have put this in units of grams per square meter, because I find these units seductively attractive and easy to use. If you want this in other metric units, you'll know how to make the conversion; if you need this in pounds per 1000 ft2, divide the g/m2 units by 5. That is, 20 grams per square meter is equal to 4 pounds per 1000 ft2.

The Shiny app will update as you change the grass species, soil test K, and annual N application. You will see the calculated fertilizer requirement change. The text will change, and so will the plot. I've adjusted the plot below to show the output generated when the input is grass species of bentgrass, soil test K of 48 ppm, and annual N application rate of 16 g/m2.

PlotThere is a horizontal line at 0, just to mark that level. The diagonal line is fixed for that particular species and that particular nitrogen rate, showing how the K requirement will change if that much nitrogen is applied and the soil test K changes in the range of 0 to 200 ppm. The actual point of 48 ppm soil test K corresponds to an annual K requirement of 7 g/m2, which can be read in the text on the app. 

Try the mlsn_K app for yourself.

All the code used to make this app, and the calculations to determine the fertilizer requirements, are available on GitHub.

On the seductive attractions of metric units

Growing up and first working in the turfgrass industry in the United States, I naturally used US customary units: inches and feet, pounds and ounces, fluid ounces and gallons and so on. I started to use metric units when I went to work as a golf course superintendent in China and Japan, and I have been using these units ever since. 

I like to use 1 square meter (1 m2) as the base unit. There are a few reasons for this. First, I can see one square meter, I can imagine it, and I can think of how that base unit will be managed. Then it is simply a matter of considering how many of those base units of 1 m2 are to be managed. Second, the numbers work out in a convenient way in three dimensional space. I’ll elaborate on the convenience of this below. Third, I like to work with numbers from 1 to 100, as much as possible, and working with 1 m2 as the base unit is convenient in this way. Nitrogen might be applied at about 3 g per m2 per month; in Thailand one might apply 30 to 50 grams of nitrogen per m2 in a year. Wetting agents will be applied at about 2 mL per m2. Spray volumes will usually be from 40 to 80 mL per square meter. These numbers fall in a range that is easy to work with, and easy to think about. There are no 100s, no 1000s, no 10,000s, and few numbers less than 1.

1 L of water is 1 mm in depth across 1 square meter and will increase soil moisture in the top 10 cm of 1 square meter by 1%

Now for the three dimensonal space of the rootzone. For managed turfgrass, the root system, averaged over the course of a year, can be considered to be 10 cm deep. This is where most of the nutrients will be taken up, where the grass will obtain water, where coring and cultivation practices will be done. Maybe you will like to use a rootzone depth of 7.5 cm, or 15 cm, or 30 cm. That’s fine, and can be done, but using 10 cm has some attractive properties. 1 m2 to a depth of 10 cm has a volume of 100 L. If the volumetric water content (VWC) of the soil is 18%, that means there are 18 L of water in 1 m2 to 10 cm depth. Want to increase the soil moisture to 22%? That will require 4 L per m2.

In 2-dimensional space, this is convenient also. 1 L of water spread over 1 m2 has a depth of 1 mm. If it rains 6 mm, that is 6 L of water per m2. And if the soil VWC drops from 20% to 16% from morning to evening, that is a water loss of 4 L, equivalent to 4 mm at the surface. That's the evapotranspiration (ET). Not some estimate from a computer, but the real consumptive water use. 

Want to compare the ET of a full sun area to the ET of a shaded area? Measure the difference in VWC from morning to evening at both sites. Now you've got the answer.

Thinking of water application in mm and L translates directly to the VWC in the soil if one is assuming a 10 cm rootzone. Of course, a soil moisture meter may have rods at a 6 or 7.5 or 12 cm depth; one can make appropriate adjustments in assumptions and estimates.

3 fine football fields

On the eve of the World Cup, I have three quick things to share about football/soccer. 

Kashima Soccer Stadium, March 2014

1. I've been to two matches at the Kashima Soccer Stadium (this was a venue for World Cup games in 2002) in the past year, one at the end of summer, and one at the beginning of spring. The grass is a mixture of 2 kentucky bluegrass (Poa pratensis) varieties and one hybrid bluegrass variety. In this part of Japan it would be typical to use warm-season grasses on sports fields – summer temperatures are similar to those in Atlanta – and on the surrounding golf courses and lawns, warm season grasses are grown. I've been impressed at just how good the turf is here. Almost all the stadiums in J.1 are bermudagrass, so this pitch at Kashima Stadium is exceptional in being cool-season grass, and exceptional in being maintained to such a high standard. 

2. In the Thai Premier League, one can find matches played on bermudagrass, zoysiagrass, and seashore paspalum. Muangthong United play at the SCG Stadium on the north side of Bangkok, and the pitch here is seashore paspalum.

Seashore paspalum at SCG Stadium in Bangkok, April 2014

To keep the ball moving quickly, water is added at halftime. 

Irrigation at halftime, SCG Stadium

This is the best pitch I've seen in Thailand.

3. If you haven't watched this feel-good story about the amazing Panyee FC in an amazing part of Thailand, take a couple minutes and watch it now. I bet you haven't seen football played like this.