This week I spoke to a full room of turfgrass managers at Bangkok's Thana City Golf and Sport Club about an important topic: understanding data for use in turfgrass management. I've recorded this video of the presentation slides in which I discuss the two classes of data that can be collected – data about playing surface performance, or data about plant growth – and then I go into some detail about soil moisture and photosynthetically active radiation (PAR), with a brief mention of salinity and soil pH at the end.
There were many questions and an active discussion in this seminar and in fact lunch time arrived before I could speak about salinity and soil pH, so this video provides the narration of what I would have talked about had there been more time.
David Lau from Spectrum Technologies, pictured with me at right, gave an interesting presentation in which he talked about a broad range of meters and software that can be used to collect and analyze information for improving turfgrass performance. This is part of what PACE Turf call Precision Turfgrass Management (PTM), which is a systematic effort to provide optimum turf performance using minimum resources. As David mentioned, we cannot manage something if we do not measure it.
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.
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.
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.
I assume no Na is added as fertilizer.
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.
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.
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.
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.
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.
Sand rootzones are common the world over for golf course putting greens. Many athletic fields are also built with a sand rootzone, and in Asia, many of the tees, fairways, and even roughs are grown in a sand rootzone. Is sodium a problem for structure of these soils? The answer is a resounding NO.
From the chapter Warm-season Turfgrass Fertilization by Snyder et al. in the Handbook of Turfgrass Management and Physiology, we learn that the "very sandy soils that often are used for golf greens and athletic fields have no structure and are largely unaffected by sodium."
Research presented at the 2012 Crop Science Society of America Annual Meeting by Obear et al. also showed that extremely high levels of sodium have no effect on the saturated hydraulic conductivity of sand rootzones. In this paper, Effect of Sodium On Saturated Hydraulic Conductivity of Sand-Based Putting Green Root Zones, sand, sand with various amendments, and a silty clay loam, were saturated with waters of varying sodium levels. The saturating solution with the highest amount of sodium had a sodium adsorption ratio (SAR) of 80, which is extremely high.
There are a few reasons to pay attention to sodium. In soils with appreciable levels of clay, soil structure can be negatively affected by sodium. If rapid blight is a possibility at one's property, then the soil sodium should be kept at less than 110 ppm. And one should be aware of the electrical conductivity (ECw) of the irrigation water and of the soil (ECe). Sodium can be a major contributor to that, and if the ECe approaches the threshold level for a species, steps should be taken to manage the soil salinity.
But sodium and soil structure in sand rootzones? That is not something to be concerned about.
Occasionally I get to travel to places that have a tremendous variety of grasses. One of these is Hawaii – a wonderland of grasses. But at Hawaii it is a panoply of warm-season grasses. Recently I visited Catalonia, at the invitation of David Bataller, Golf Courses and Grounds Manager of the PGA Catalunya Resort. What I saw was really amazing! Almost every warm-season and cool-season turfgrass was growing in this region.
It is always interesting and a great learning experience to see so many types of grass. One thing that remains consistent about places where a lot of grasses, both cool- and warm-season species can grow, is this: these are among the most difficult places in the world to produce good year-round playing surfaces.
At this 36-hole facility, David manages primarily cool-season grasses, but there are also warm-season grasses – in fact, I counted ten different species of turfgrass, in total, being used on the property, plus lovegrass (Eragrostis) put to good use in many landscaping and out-of-play areas. In no particular order, they are:
Lolium perenne (C3)
Zoysia japonica (C4)
Pennisetum clandestinum (C4)
Poa annua (C3)
Poa trivialis (C3)
Poa pratensis (C3)
Agrostis stolonifera (C3)
Cynodon dactylon (and Cynodon hybrids) (C4)
Paspalum vaginatum (C4)
Festuca arundinacea (C3)
Why are there such a wide variety of grasses used for turf in Catalonia? If we look at a chart of growth potential through the year (Figure 1), it would seem that cool-season grasses would be a clear choice for this area.
Figure 1. Temperature-based growth potential of C3 and C4 grasses based on climatological normals data for Girona, Spain.
The chart shows that the cool-season growth potential is higher than warm-season growth potential throughout the year. But what we find growing are both cool- and warm-season grasses. This is similar to a place like San Diego, California, where we can find seashore paspalum and bermudagrass and kikuyugrass growing alongside perennial ryegrass, Poa annua, and creeping bentgrass.
The reason warm-season grasses perform well in this type of climate is because of water. Warm-season grasses have better water use efficiency than do cool-season grasses, and warm-season grasses generally have better salinity tolerance than do cool-season grasses. So in a climate where the evapotranspiration is higher than the precipitation, and where the irrigation water has some salt in it, warm-season grasses will compete well with and may even outperform cool-season grasses.
During the winter season, the warm-season grasses go dormant, as we can see with the Zoysia japonica on the bunker slope, but it is not cold enough for there to be any winterkill.
There was even a local type of seashore paspalum (seedhead at right) that grows well in this area, and in fact some of the older golf courses near the sea in Catalonia have this native grass.
After the vist to PGA Catalunya Resort, my head was spinning. We had seen so many types of grasses, seen sunrises over the frost-covered courses, had discussed the soil and water salinity challenges, and tried to predict how certain grasses would grow at different times of the year. Maintaining fine turfgrass in a transitional climate, especially one without much precipitation, is really a challenge.
During my visit to Gran Canaria, I visited all seven golf facilities on the island. It is interesting to consider how the different grasses are performing. Although Gran Canaria has an exceptionally salubrious climate for people, it actually can be a difficult place to manage turfgrass.
The main turfgrasses being grown on the golf courses are:
kikuyugrass (Pennisetum clandestinum)
seashore paspalum (Paspalum vaginatum)
bermudagrass (Cynodon spp.)
creeping bentgrass (Agrostis stolonifera)
The first three of these are warm-season grasses, meaning they grow most rapidly with an average temperature of more than 27°C. Creeping bentgrass is a cool-season grass, and it grows best at a temperature of around 20°C.
There are three interesting things that we can note related to the grasses and the temperature here.
1. When we plot the temperature-based growth potential of cool-season and warm-season grasses based on climatological normals weather data at Las Palmas, we see that the growth potential for cool-season grass is higher than that for warm-season grass for each month of the year. For more about growth potential, see this article by Dr. Wendy Gelernter and Dr. Larry Stowell of PACE Turf.
Figure 1. The temperature-based growth potential for C3 and C4 grasses based on climatological normal temperatures from Las Palmas de Gran Canaria.
2. The grasses on the golf courses of Gran Canaria are almost all warm-season, but the growth potential model predicts that the temperatures are ideal for cool-season grasses. Why is it that we find the warm-season grasses predominating?
It is because of water. The eastern and southern parts of the island, where the golf courses are located, receive very little precipitation. Supplemental irrigation is required to keep functional golfing surfaces, and that irrigation is both limited in supply and rather high in salinity. Some irrigation supplies on the island have an electrical conductivity of almost 4 dS/m.
Warm-season grasses such as bermudagrass and seashore paspalum have lower water use rates than do cool-season grasses, and these warm-season grasses are also more tolerant of salinity. This allows the golf course turf to be maintained with a minimum of water. This benefit is enhanced by the rather cool temperatures during the winter months, and in fact, for seven months of the year at Gran Canaria, the warm-season grasses grow at less than 50% of their potential, which means they use less water. The relatively low growth potential for warm-season grasses mean they will use less fertilizer also.
3. The resort courses at the southern part of the island see high traffic during the months of October to April. This creates a challenge for greenkeepers because the very season at which traffic is highest is also the season at which the primary turf of bermudagrass or seashore paspalum has its slowest growth.
Micah Woods, Alejandro Nagy, and Fernando Suarez on a seashore paspalum tee at Maspalomas Golf
As I spoke with greenkeepers around the island, and as I mentioned in my radio interview with Chicho Morales on Bajo Par Canarias, the most important thing in managing good turf on Gran Canaria is water. Applying the right amount of water to the turf, and managing the salts that are applied in the irrigation water, by leaching, will lead to the best possible turfgrass conditions.
Listen to the radio show here, with extended comments from me starting at about the 10:00 mark, some good questions from host Chicho Morales, and translation and additional remarks on my visit by Alejandro Nagy and Daniel Carretero.
I visited Gran Canaria and its seven golf courses this week, choosing this island in particular because of its many microclimates and consequently the chance to study a variety of grasses in different environmental conditions.
Location (in blue) of the 7 golf facilities on Gran Canaria
I also have friends (*see below) on this island, which made it an even more appealing place to visit. The north side of the island sees more clouds, and the south side of the island has more sunshine, and in general, it is a rather dry island. At the airport, near Telde in the East, the average annual rainfall is 134 mm. Contrast this with Bangkok, where grasses, many of them the same as at Gran Canaria, grow in a climate with almost 1,500 mm average annual rainfall. In fact, at Bangkok, there are six months of the year, each of the months from May through October, that have average rainfall more than the 134 mm annual average at Telde.
That lack of rainfall makes irrigation crucial to the performance of any turfgrass as a sporting surface at Gran Canaria, and because almost all of the courses are irrigated with treated wastewater, which is rather high in salinity, careful attention to water quality is just as important as water quantity, as is choosing the grass species that can tolerate such salinity.
At the seven golf clubs on the island, there are nine courses. Salobre is 36 holes, and Anfi Tauro has a short course. The grass breakdown is this. On greens, four courses are creeping bentgrass, four are seashore paspalum, and one is bermuda. Through the green, one course is kikuyugrass, four are bermuda, and four are seashore paspalum.
There is some Poa annua growing, mixed in with bentgrass on some greens, and as a weed in some fairways. I also saw some perennial ryegrass, although it was not thriving. And there was Stenotaphrum secundatum (St. Augustingrass in the USA, buffalograss in Australia) growing well in a few parks, but I did not see it on any golf courses.
At Real Club de Golf de Las Palmas, some unirrigated picon areas between tees and fairways have drought-tolerant bermudagrass growing in these dry conditions. The tees and fairways, which receive irrigation, are covered with kikuyugrass. A collection of photos are posted at Flickr (and below) where you can see the grasses and the golf courses of this diverse island.
*Alejandro Rodriguez Nagy, who arranged the schedule this week and introduced me to the greenkeepers at each course; Daniel Carretero, who played on the golf team at the University of Portland (my hometown) and worked at Augusta National GC where I met him during the 2011 Masters Tournament; and Oscar Sanchez, who I caddied for at Waverley CC when he played in the 1993 USGA Junior Amateur Championship.
This short video will be of interest to golf course architects, superintendents, and anyone involved in the management or development of golf courses in tropical and sub-tropical Asia. Cut to just eight minutes in duration, it is a narrated walk along 5 km of Ishigaki island coastline, describing the grasses encountered and showing the ecological setting in which these grasses grow naturally.
We have worked with PACE Turf to develop the Minimum Levels for Sustainable Nutrition (MLSN). These new guidelines ensure ample amounts of mineral elements are present in the soil to meet the requirements of turfgrass. The target for calcium is 330 ppm using the Mehlich 3 extractant, meaning that if calcium is present in the soil at 330 ppm or more, none is needed as fertilizer, because the soil can supply all the calcium that the plant requires.
Calcium is also used to replace sodium in the soil. For that use of calcium, it is not a fertilizer, but rather a soil amendment. And the MLSN guideline for sodium is to have no more than 110 ppm in the soil, measured in a Mehlich 3 extract.
What if you have sodium at more than 110 ppm in the soil, perhaps from salt spray, or more likely, from sodium in the irrigation water? A new document from PACE Turf explains how to calculate the calcium requirement. That document, however, uses pounds and acres and thousands of square feet. I make the calculations here in metric units.
First we look at how much sodium is in the soil. Our goal in this calculation is to find out how much calcium we need to apply to match the amount of excess sodium. If we can apply calcium to match the sodium, then it will be easier to leach the sodium from the soil.
Let's pretend we have just received a soil test report and the sodium is at 150 ppm. This means that there are 150 mg of sodium for each kg of soil, and our excess sodium is 40 ppm (or 40 mg) more than the 110 ppm maximum on the MLSN guidelines. 150-110 = 40 mg/kg
We can take that 40 mg of sodium and find out how many ions it is. One millimole of sodium has a mass of 23 mg, so we have 40/23 = 1.7 millimoles of sodium per kg. Let's write millimole as mmol for simplicity. Now we are ready to calculate how much calcium we require.
Sodium is a monavalent cation, meaning it has one positive charge for each ion. We have 1.7 mmol of sodium, and also 1.7 mmol of positive charge. We need 1.7 mmol of positive charge from calcium. But calcium is a divalent cation, with two positive charges for each ion. So we only need 0.85 mmol of calcium. One mmol of calcium has a mass of 40.1 mg, so we need 40.1*0.85 = 34 mg of calcium. We've almost got it: 34 mg of calcium will provide the same amount of charge as will 40 mg of sodium.
We now need to consider how much area and volume of soil we will apply that calcium to, so that we can get an application rate. Let's assume we have a rootzone 15 cm deep and with a bulk density of 1.33 g/cm3. In that case, 1 m2 of the soil has a mass of 200 kg. Remember, we've previously been making our calculations on a per kg basis. Now we want to change to square meters. To replace the excess sodium, we have already calculated that we need 34 mg of calcium per kg of soil. And we have 200 kg soil in 1 m2, so we need 34*200 = 6,800 mg calcium per square meter (6.8 g/m2).
That's how much calcium we require in this example. If you want to simplify this and not work through the calculation every time, we can simply apply 0.17 mg of Ca for every 1 ppm sodium in excess of 110 ppm. If sodium were at 120 ppm on the soil test, the calcium requirement would be (120-110)*0.17 = 1.7 g/m2. If sodium were at 204 on the soil test, the calcium requirement would be (204-110)*0.17 = 16 g/m2.
Of course, if you have more than 330 ppm Ca and less than 110 ppm Na on the soil test, then there is no calcium requirement. The soil already has enough, and the sodium does not require treatment.
I was at Mauritius last month and visited most of the golf courses on the island. Mauritius has some of the most visually striking golf courses I have ever seen. I was surprised (and impressed) to see beautiful evaluation plots of grass at Paradis Golf Club, where course superintendent Ajaye Ladsawut is maintaining a nursery with different varieties of bermudagrass, seashore paspalum, and even some zoysiagrass. This is an amazing site for turf research plots, right at the base of a World Heritage Site, the rugged Le Morne Cultural Landscape (see below) which served as a shelter for runaway slaves. The grasses are being grown on two different rootzones, a dark rock sand (foreground above) and a calcareous coral sand (background above); the purpose of the grass evaluation nursery at Paradis Golf Club is to determine which grasses perform the best, and in what soil, for a new course in planning stages now and for possible course improvements at Paradis.
The Paradis Golf Club has seashore paspalum (originally from Durban CC) on the greens, a local bermudagrass is the primary species on tees and fairways, and there are also areas of blue couch (Digitaria didactyla), St. Augustine or Buffalo grass (Stenotaphrum secundatum), Zoysia matrella, and Sporobulus. The irrigation water is rather high in salt as the course sits right on a lagoon, but all these grasses manage to grow well.
The grass evaluation plots at Paradis are very well-maintained and are given nearly the same maintenance treatments as the grass on the golf course. The Bel Ombre paspalum is from a nearby golf course and has a slightly different growth habit and stolon color compared with the Durban CC paspalum on the greens at Paradis.
This is a seashore paspalum fairway (with patches of bermudagrass at right) on Ile aux Cerfs, also at Mauritius. One of the most challenging things in the management of seashore paspalum is to keep other grasses out. The native bermudagrass here is quite salt tolerant and grows vigorously. Rock salt is used here to control most weeds in the seashore paspalum, and the use of salt is a good strategy for weed control in seashore paspalum when soil conditions allow it. Seashore paspalum is beautiful but it can also be a high maintenance grass and will tend to be overtaken by other grasses when grown without intensive and expensive maintenance.
Another article about sodium chloride applications as a method of weed control in seashore paspalum has been published in Weed Technology. This research was done at Hawaii by Dr. Jim Brosnan, and I did some additional testing at Thailand and helped with the paper entitled "Sodium Chloride Salt Applications Provide Effective Control of Sourgrass (Paspalum conjugatum) in Seashore Paspalum Turf". Granular applications of sodium chloride at a rate of about 50 g m-2 can cause severe damage to many weeds without causing phytotoxicity to seashore paspalum. In our research at Thailand, we first wet the leaves of the grass, then apply granular sodium chloride (table salt) and allow it to sit on the leaves of the grass. Because the leaves are wet, the salt will stick to leaves, as shown below, with salt applied to seashore paspalum (variety Salam) mowed at 15 mm. In our experiments, we see no phytotoxicity to the seashore paspalum, but the same rate of sodium chloride applied to bermudagrass or carpetgrass (Axonopus compressus) or to some broadleaf weeds will cause severe phytotoxicity or plant death.
The photo above shows sodium chloride crystals sticking to the wet leaves of a seashore paspalum fairway turf. If salt is used to control weeds in seashore paspalum turf, I think it will work best if applied when the weeds are still small. If weeds are allowed to proliferate, and sodium chloride is used to control the larger patches of weeds, then unsightly yellow patches will occur all over the turf. As with any weed control program, it is important to catch the weeds early. Earlier this week I was at Mauritius and visited Le Touessrok Golf Course at Ile aux Cerfs (see below); this is a seashore paspalum golf course where salt is regularly used to control bermudagrass (Cynodon spp.), St. Augustine grass (Stenotaphrum secondatum), and broadleaf weeds from encroaching into the seashore paspalum turf. One thing to remember of course is that too much sodium in the soil can cause problems with soil structure in clayey or silty soils. Sodium chloride applications may work best on sandy soils, where there is little chance of any soil structural problems.
