Viridescent - the Asian Turfgrass Center blog

Calcium for Turfgrass: is there enough in the soil?

The answer, almost certainly, is yes. These calculations of how much calcium the grass uses, compared to how much plant-available calcium is in the soil, leave little doubt that there is almost always more than enough calcium in the soil to meet the needs of the grass.

How much calcium does grass use?

Let's take a turfgrass site at which clippings are removed, and estimate how much calcium is removed, or harvested, in one year. A reasonable estimate for annual clipping yield of maintained turfgrass is about 400 g m^-2. A reasonable estimate for calcium in the dry matter of turfgrass clippings is about 4500 ppm = 4.5 g kg^-1 = 0.45%. So if we harvest, over the course of a year, 400 grams of clippings from each square meter, and if those clippings contain on average 0.45% calcium, then the mass of calcium harvested from one square meter each year is:

400 g x 0.0045 = 1.8 grams of calcium removed each year

How much calcium is in the soil?

We've just calculated that in the situation where we remove the clippings from a maintained turfgrass area, we may be removing about 1.8 grams of calcium from each square meter each year. Let's now imagine that our root system is 10 cm deep, and that the bulk density of the soil is 1.5 g cm^-3. In one square meter, then, to a depth of 10 cm, we have a volume of 100 L, and a mass of 150 kg. Let's say this is a sandy soil, with a relatively low cation exchange capacity, and that the plant-available calcium (the calcium that is in soil solution and on cation exchange sites) is at a concentration of 400 ppm = 400 mg kg^-1. How much calcium is that?

150 kg of soil x 400 mg/kg = 60,000 mg of calcium = 60 g of calcium

Three Decades

That's how long it would take, 33.3 years, to be precise, for the grass to use 60 grams of calcium if harvested at the rate of 1.8 grams of calcium per year. There is much more calcium in the soil than is required for healthy turfgrass, even in soils that have relatively low amounts of calcium.

Chemical Fertilizer Programs for Sand Based Rootzones - the 1 minute version

Last week at the Tennessee Turfgrass Association conference I gave a 30 minute presentation with the title Chemical Fertilizer Programs for Sand Based Rootzones. But this topic doesn't always require 30 minutes to explain - I like to distill this topic into the most important principles. There is plenty of experimental and empirical evidence to show that these four principles, if followed, will give excellent results.

1. Apply the right amount of nitrogen
2. Ensure soil pH is more than 5.5 and less than 8.3
3. Ensure soil potassium (as measured by the Mehlich 3 extractant) is kept above 50 ppm
4. Ensure soil phosphorus (as measured by the Mehlich 3 extractant) is kept above 35 ppm

The End (of the 1 minute version of this topic)

If you are especially interested in mineral nutrition for turfgrass or soil nutrient analysis for sand rootzones, you may want to read or watch some of these more lengthy expositions.

Simple Fertilization: Use the Nutrients Already in the Soil, from the Hawaii GCSA newsletter

PACE Turf Potassium Sufficiency Video, on Youtube

Soil Testing: It Does Not Have to be Difficult, on Youtube

Creating an Excellent Playing Surface: Managing the Plant, especially section 2 regarding nitrogen application

Does Potassium Fertilizer Really Increase Roots?, from TurfNet Monthly

And for those who really want to reduce P and K, consider the implications of The Park Grass Experiment and the Fight Against Dogma, written with Dr. Frank Rossi and published in the USGA Green Section Record

Potassium for Turfgrass: interview with Dr. Larry Stowell of PACE Turf

Dr. Larry Stowell and I recorded this video interview about potassium fertilizer for turfgrass. How much potassium is enough? How should you decide how much potassium to apply to meet the plant requirements, without wasting money by applying too much? Is potassium fertilizer necessary at all? Watch this video to find out, and check out PACE Turf for a wealth of valuable turfgrass information.

What's the Most Accurate Way to Measure Available Nutrients in the Soil?

Have you seen this picture before? I used this photo in the announcement for turf science seminars I gave at Japan last winter, and a golf course superintendent asked me this week about what is shown in this photo. This is a cation exchange membrane in general, and is specifically a PRS (Plant Root Simulator) probe from Western Ag Innovations. In my research at Cornell University, I used these exchange membranes to measure potassium flux in the soil. 

The results of this experiment were summarized in a paper we published in Applied Turfgrass Science. Exchange membranes are quite sensitive to changes in nutrient supply, and one could make a strong case for exchange membranes being a more accurate way to measure the really available nutrients in the soil compared with conventional soil testing techniques. Potassium supply to the roots, for instance, is affected by the activity of K⁺ in soil solution, leaching, soil temperature, soil water content, root uptake of K⁺, release of K⁺ from mineral forms in the soil, and other contributing factors. Exchange membranes, by measuring the nutrient flux over time, are able to capture much of the true variabiability in nutrient supply, similar to what grass roots would experience.

In our experiment, we found that the very sensitivity and accuracy of the exchange membranes makes them less practically useful than a conventional soil test in predicting whether potassium should be applied or not. To summarize the results of our experiments with cation exchange membranes, we found that:

1. Potassium supply increases when potassium fertilizer is applied.
2. The effects of potassium fertilizer can be long-lasting, even in a sand with low CEC (1.2 cmol_c kg^-1). We detected increases in potassium supply rate six months after an application had been made. I think most people would expect the potassium to leach or otherwise have no effect on supply rate six months after application in a low CEC sand.
3. Potassium supply rate can be sufficient to meet plant requirements in many sands because of potassium release from mineral forms in the soil.

Turfgrass Archaeology

This soil profile, showing how the soil has been modified after about 70 years of management as a golf course putting green, is absolutely fascinating. This photo is from a course at Sydney, Australia. Because this hole is now closed for a complete renovation, the superintendent decided to make some archaeological researches by digging down to the original dune sand that the green was built on. Click on the photo above or click here to get a full size image for closer inspection.

Starting from the bottom of the profile, we can see the clean sand that is the original dune, meters deep, that the green was planted on. Moving up, we see darker material at the base, this probably being some organic material that was mixed in the soil at the time of planting the green. Then we start to see distinct layering, dark and then white bands moving horizontally across the profile; these would be the bands of sand topdressing laid down at annual renovations, as the scarifying-aerifying-topdressing activity is often referred to in Australia. And we start to see aerification holes, filled with sand from decades ago, still providing that vertical channel through the soil profile that is so critical to rapid air and water movement. 

Moving up through the central part of the profile we can see perhaps a change of topdressing sands, perhaps some periods when more coring was carried out, and less topdressing sand was laid down, and then nearer the surface we see even more coring holes filled with sand, and what appears to be a higher organic matter content, still diluted with sand, but perhaps less so than lower in the historical profile.

This profile is one of the most interesting things I've seen on a golf course, and it helps to remind me that the maintenance work we do on a daily basis will have an impact on how water, nutrients, and air (and consequently roots) move through the soil profile for years to come.

How Much Potassium Does Turfgrass Need?

Potassium is the mineral element found in the second-highest concentration in turfgrass leaves; only nitrogen is at a higher concentration. But how much potassium fertilizer is enough? Dr. Doug Soldat from the University of Wisconsin wrote a post for the Turf Diseases website entitled How I'd Manage Potassium on Cool-season Turf, and he has expanded on that in an excellent article in the May/June issue of The Grass Roots.

Dr. Soldat makes a quick review of when and how potassium is likely to provide improved cold, heat, drought, and wear stress. You might be surprised to find that the research results aren't very strong or conclusive in supporting the idea that high levels of potassium fertilization confer these increased stress tolerances to cool-season grasses. There is no doubt that potassium is an important mineral element, but if there is already enough potassium available to the grass, adding more doesn't seem to have much of an effect. For example, we can read in textbooks that more potassium will lead to a more extensive root system, but is that really the case? 

Does potassium fertilizer really increase roots?, I asked, in this article from TurfNet Monthly. My conclusion was that potassium fertilizer will do nothing to increase roots, and in fact may actually cause a decrease in rooting, unless the potassium was being applied to correct a potassium deficiency. Potassium application to turfgrass is likely to increase rooting only when it eleminates a potassium deficiency. I would classify a turfgrass soil as requiring additional potassium at about the 50 ppm level using the Mehlich 3 soil test extractant. If the soil is less than 50 ppm potassium, we might expect some response from a potassium fertilizer application. If the soil has more than 50 ppm potassium, the grass can almost certainly get all the potassium fertilizer it requires from the potassium that is already in the soil, and potassium fertilizer would be unlikely to influence turfgrass performance. 

Try This Technique for Improving Drainage

It is always a challenge to manage areas with poor drainage, and on sandcapped turfgrass areas the drainage can be quite problematic once organic matter builds up over the sand layer. Topdressing and aerififying and verticutting can all be used to dilute or remove organic matter, but when the organic layer gets too thick, it holds a lot of moisture, negating the value of the sandcap and creating an ideal growing environment for weeds.

The image above shows how an organic layer develops on a sandcapped fairway, and the image at right shows how weedy species have colonized the surface of what was once a zoysia fairyway. The buildup of organic matter over sandcapped fairways is why I have often suggested that sandcapping is not an ideal way to construct a fairway. Sandcapped fairways require more maintenance and deteriorate over time. Topdressed fairways, on the other hand, require less maintenance and improve over time.

But no matter what type of soil you have, this tip from Larry Gilhuly at the USGA is one that might be useful for you. Have you ever encountered areas with excessive organic matter buildup that slows water from infiltrating into the soil? Gilhuly asks,

"Can this condition be easily fixed at no cost or should all of these locations have complete renovation? . . . Sand topdressing and regular aeration are used to help negate the problems of excess organic material, but often this is not enough. After testing several methods to dry these areas, Rich Taylor, CGCS, struck upon the idea of using cup cutters spaced every one to two feet to go as deep as possible. The excessive organic material and some soil is removed and replaced with sand. This change essentially creates multiple dry wells in the area. If the soil underneath has reasonable permeability, the results are fast and effective. Follow-up sand topdressing is then practiced to minimize future layers. In the past few years, previous wet areas around the greens are now gone by using this simple technique."

Read the entire article on the USGA website here.

New Information on Diseases and Cation Exchange Capacity

I've been really busy in the past month, returning to Thailand after the exciting Masters Tournament, traveling to Singapore, Vietnam, and Sri Lanka, studying, and writing. Thanks to @daisukeiw who sent me the image above of the layout for my new series in Golf Course Seminar magazine. Pitchcare Oceania have just published a panel report on cation exchange capacity (CEC) and have featured some comments from me about CEC in sand rootzones and how it can be estimated most accurately by using an equation in which the only variables are soil pH and soil organic matter content.

I've also made some international updates to the Turf Diseases website. Some of my recent posts on that site are:

Large Patch Resistance of Zoysia?

A Cornucopia of Disease in Southeast Asia

Healthy Grass = Little Disease

Potassium, Hokkaido, and Snow Mold

Turfgrass Diseases in India

What is the Most Interesting Disease in the World?

Mites, a Corpse Plant, and Native Grasses

Large Patch on Zoysiagrass

More About Seashore Paspalum

A Most Unsightly Disease

The Wow Factor, Seashore Paspalum, and Dollar Spot

Sandcapping or topdressing: which is better?

I have often advocated sand topdressing rather than sandcapping for golf course fairways and roughs. Why? Because sandcapping at the time of construction makes for a much higher construction cost, higher maintenance cost, and invariably leads to deteriorating playability over time. Conversely, a sand topdressing program provides better playing conditions, easier maintenance, and all for a much lower cost. I am not referring to drainage. Drainage is required for both a sandcapped system and a topdressed system. But sandcapping is not drainage.

Sandcapping a turfgrass area with 10 to 15 cm of sand has a high upfront cost and then forces higher maintenance costs as well, for that sandy rootzone will require more fertilizer, more irrigation water, and more surface organic matter management than would an area not sandcapped. And what happens if the organic matter is not controlled? See below. What used to be a fine zoysiagrass is now a mixture of cowgrass and sedges. A layer of organic matter built up at the surface creates a perfect growing environment for weeds that thrive in wet soils. And all that sand underneath? One might as well bury money in the ground. Once the organic layer builds up over the sand, there is no benefit whatsoever to having the sandcap.

Dr. Alec Kowalewski has recently published some intriguing articles that show just how effective sand topdressing can be as an alternative to sandcapping. Not only does he demonstrate the substantial cost benefits of a topdressing (or built-up over time sandcap) program compared to a sandcap installed at the time of construction, his research also shows how turf quality improves and drain line spacing can be extended when a topdressing program is implemented. 

"Preliminary findings from this research," he wrote, "suggest that as little as 1/2” (1.25 cm) of sand can be used to improve athletic field playability by substantially decreasing the surface moisture content." His results show that once 2.5 cm of topdressing sand has been applied, drain line spacing at 3.9 meters provided sufficient drainage and surface stability. After a 5 cm topdressing layer was established, and assuming surface slope is at 1% or greater, then drain line spacing could be extended to more than 6 meters while still producing the desired surface conditions.

For full details, see:

Kowalewski, A. R.; Crum, J. R.; Rogers, J. N. III. 2010. The built-up sand-capped athletic field system. MSU Turfgrass Science Program. April 7. p. 1-7.

Kowalewski, A. R., J. N. III Rogers, J. R. Crum, and J. C. Dunne. 2010. Sand topdressing applications improve shear strength and turfgrass density on trafficked athletic fields. HortTechnology. 20(5):p. 867-872.

Kowalewski, A. R., J.R. Crum, J. N. III Rogers, and J. C. Dunne. 2011. Improving native soil athletic fields with intercept drain tile installation and subsequent sand topdressing applications. Soil Sci. 176(3): p. 143-149.

With sandcapping at the time of construction there is a high upfront cost, turfgrass and playing conditions that deteriorate, and there will be the need for a disruptive and costly renovation to remove the organic layer that will invariably develop at the surface. Planting grass onto native soils and then topdressing with sand results in lower construction costs, lower maintenance costs, and better playing conditions over time with longer intervals between disruptive renovation projects. It is the surface conditions that matter for the playing of sports on grass, and topdressing with sand is a proven method to create the desired surface conditions.

Plant Available Nutrients in Sand Rootzones

Golf course putting greens and other high-use turf are generally grown in a sand rootzone. In Asia, many courses also have tees, fairways, and sometimes even rough areas plated with sand as well. This poster, which I prepared for the Oregon State University turfgrass field day in 2005, shows some interesting results on the measurement of plant-available nutrients in sand rootzones. In this poster I showed data looking specifically at calcium, magnesium, potassium, and sodium. Download the poster in PDF format by clicking here (1.6 MB).

The soil nutrient analysis (soil testing) procedures used at commercial laboratories were developed for soils that contain clay and silt particles. The sands used on golf courses and other fine turf areas are expressly selected to be relatively free of clay and silt. The data in this poster show that conventional soil test extractants such as Mehlich 3, normal ammonium acetate, and sodium acetate (Morgan extractant) overestimate the available nutrients in sand rootzones.

For the purpose of making fertilizer recommendations, it doesn't really matter whether the extracted nutrients are plant available or not, as long as the fertilizer recommendations are accurate. But for estimating cation exchange capacity (CEC), it is clear that conventional soil tests overestimate the CEC of sand rootzones. Sand has an effective CEC of zero. Therefore, we can use an empirical relationship based on the contribution of soil organic matter to CEC. For a quick and accurate estimate of the CEC of a sand rootzone, use this equation:

CEC = (-311 + (268 × pH)) × (OM ÷ 1000)

where,

CEC units will be cmol_c kg^-1 which is equivalent to meq/100 g

pH is the sample pH

OM is the organic matter percentage of the sample, in %

In tests conducted at Cornell University on sands collected from golf course putting greens around the world, we found that the simple equation above is a more accurate predictor of the sample CEC than are conventional soil tests. So if you really want to know how many nonacid cations (calcium, magnesium, potassium, and sodium) can be held in a sand rootzone, use that equation. All you need to know is the soil pH and organic matter content.