Salinity

Do you know how much salt is in your irrigation water?

Selection_084My column in the March-April issue of GCM China is about salt. The salt in water is invisible, so one needs to test the water to find out how much salt is in it.

As I wrote in the article, water with total dissolved solids (TDS) of 800 ppm would add 56 g salt/m2 (11.2 pounds salt/1000 ft2) in a 2 week period if irrigation is applied at 5 mm/day. Being aware of how much salt is in the irrigation water is the first step in determining if leaching will be required.


Is sodium an imaginary problem?

On sand putting greens, it is. The problem caused by sodium is a reduction in the downward movement of water in soils. This is caused by the deflocculation of clay in the soil. It is a real problem in soils with appreciable amounts of clay, and in those soils, an exchangeable sodium percentage (ESP) of 15% or more is indicative of potential problems. The solution? Add gypsum to reduce the ESP, and add water to leach the sodium.

But in sand rootzones, what happens when there is a high ESP? Obear and Soldat wrote about this in their recent Soil Science paper, Saturated Hydraulic Conductivity of Sand-based Golf Putting Green Root Zones Affected by Sodium.

Selection_041In this experiment, they constructed 6 sand rootzones, with 5 with amendments, and 1 without. The sand was mixed with each amendment in a 4:1 ratio by volume -- 4 parts sand, 1 part amendment.

  1. Nonamended sand
  2. Sand + peat humus
  3. Sand + Profile
  4. Sand + sphagnum peat
  5. Sand + silt loam
  6. Sand + loam

Then, "the soil cores were placed in plastic tubs and allowed to equilibrate for 48 h in a range of solutions of differing ratios of sodium chloride, calcium chloride, magnesium chloride, and potassium chloride." These solutions ranged in sodium adsorption ratio (SAR) from 0 to infinity, including two solutions with high sodium (37 mmol/L and 185 mmol/L, respectively) and no calcium, magnesium, or potassium.

After these equilibrations in solutions of different SAR, each of the soils had some cores with ESP < 15%, and some with ESP > 15%. How did the sodium influence the saturated hydraulic conductivity (Ksat) of the soils? It didn't do much, except for the sand mixed with loam, which had a clay content by weight of 4.8%. In the unamended sand, sand mixed with peat, or Profile, or silt loam, increasing ESP did not reduce Ksat. In fact, in the unamended sand, the Ksat actually increased after the soil was equilibrated with high SAR solutions.

These are some key results:

In the case of sand-based golf course putting green root zones, which often have very low clay contents, increasing ESP well above the standard sodicity threshold of 15 had no effect on Ksat.

The application of soil amendments for remediation of sodic soils (e.g., gypsum) would only be warranted for sodic soils with higher clay contents and may not provide significant infiltration benefits to sand-based golf course putting greens.

This study also provides evidence that increasing exchangeable Mg2+ [magnesium] does not affect Ksat of sand root zones.

For more about imaginary problems in turf maintenance, see:


The importance of irrigation water testing

Brad Burgess wrote:

I would appreciate your thoughts and comments re this water test. I just read your PACE Turf Article and thought I would run this by you. It could be a nice study for you re salt tolerance in Zoysia …

Never seen water this bad before and tested it after the fact. 

Others have said this water is not even suitable for Paspalum … 

Look forward to your comments. Also attached some photos … at 90 days after planting.

This water had electrolytic conductivity (EC) of 1.4, pH of 9, calcium at 4.7 ppm, magnesium 3.7 ppm, and sodium 314 ppm.

I responded:

Thanks for the photos and the water test.

Site
Photo of turf at the site being grown-in with this irrigation water.

The grass looks great. And that is a pretty poor water. It would be an interesting site to do some tests.

My thoughts on the water -- the 2 most important things to look at are total amount of salt (EC) and SAR [sodium adsorption ratio]. 

EC is what one looks at to see the effect salt in the water is going to have on the grass, how that may accumulate in the soil, and how much extra water will be required to keep the soil salts at a level the grass can tolerate.

For the salt content, it isn't too bad. The leaching requirement [for more about leaching requirement, and how to make these calculations, see this handout] for zoysia using that water, if I use a soil EC tolerance level of 8 ds/m, is 0.037, so the amount of extra water required is minimal, ET / (1 - 0.037). But if the soil structure would deteriorate, then one couldn't leach to maintain the soil EC at 8, and then the salt would damage the grass. As a comparison, the irrigation water at [golf course name redacted] has had 4 times as much salt as this water, and Tifeagle can still be maintained to a high level, as long as one leaches properly.

SAR is what one looks at to see how the sodium may cause a problem with soil structure.

I think [this lab’s water test is flawed] because it does not provide the SAR directly, forcing the customers to calculate it themselves, while emphasizing [less relevant data]. 

For this particular water, the SAR is about 26, which is especially bad for soil structure, especially because the water doesn't have a high salt content. One expects the regular use of this water to cause problems with soil structure (unless it is a sand rootzone) over time, exhibited by slowing of water infiltration. This problem can be addressed by regular applications of gypsum. The amount of gypsum to apply is based on the amount of sodium added in the water, or based on the ESP of the soil. Gypsum can be applied at pretty high rates, like 200 to 400 g/m2. I make a rough calculation that for every liter of water added, one should apply 1.5 g gypsum/m2 to prevent soil structure problems. So if 150 mm of water were added in a month, that would be a 225 g/m2/month gypsum requirement.

To summarize, I'd be concerned about soil structure with this water, would apply 1.5 g gypsum/m2 for each L of water that was applied, with that being done to prevent soil structural problems (disregard that advice on a sand rootzone), and I would make sure that slightly more water was applied than ET, to prevent salinity problems.

I’d like to emphasize three things.

1. It is really important to test the irrigation water. Because Brad had this water tested, he can identify and prevent potential problems. What is in the water is invisible. Many sites have water that is perfectly fine, and a test will confirm that. For locations with high salinity or high SAR, that problem is invisible in the water, until there are visible problems on the turf, and by then it is way too late.

Paspalum_salinity
Seashore paspalum has died at this site where salt has accumulated in the soil. This problem can be prevented by knowing what is in the water and then carefully managing the salinity through leaching.

2. Make sure the water is being tested for the right things. One needs an irrigation water suitability test. A comprehensive guide for this is Harivandi’s Interpreting Turfgrass Irrigation Water Test Results. In that, he writes:

When irrigation is applied to the soil, the best indicator of sodium effect is a water’s Sodium Adsorption Ratio (SAR), a value which should be provided in all laboratory water analyses. 

3. If for some reason SAR is not reported, one can calculate it from this equation:

\[SAR = \frac{Na}{\sqrt{\frac{Ca + Mg}{2}}}\]

where,

SAR is sodium adsorption ratio

Na is the sodium concentration of the water in milliequivalents per liter

Ca is the calcium concentration of the water in milliequivalents per liter

Mg is the magnesium concentration of the water in milliequivalents per liter


"If you want to use soil test results to develop a fertilizer program, use a different extraction method"

  1. Water_saltIs water (or a saturated paste extractant, or mixing irrigation water with soil) a good way to look at soil nutrients?
  2. What about two tests to look at "available" and "exchangeable" nutrients, is it good to look at both?

The quick answer to both of those questions is no.

The saturated paste extraction is used for measuring soil salinity (ECe). 

I think water extractions, whether with a saturated paste, one part soil with two parts water (1:2 extraction), or one part soil with five parts water (1:5 extraction), are quite interesting and informative for research purposes. But water extraction results are not useful as a decision making tool in turfgrass maintenance.

Carrow et al. wrote about this in Clarifying soil testing: 1. Saturated paste and dilute extractants. They explained that the "saturated paste extraction is not the best method for determining soil fertility levels and can be very misleading."

I wrote about this in Water-based Extraction Methods for Turf Soils. At the time I wrote that article, I was a graduate student, doing lots of research about extraction methods, and I appreciated water as an extractant a bit more then than I do now. It is great for research into soil nutrients. But "it is not possible to take the numbers and decide that they are low enough to justify fertilizer applications ... If you want to use soil test results to develop a fertilizer program, use a different extraction method."


Not entirely a surprise

At the Poipu Bay area of Kauai, most hotel lawns are seashore paspalum. This lawn at the Sheraton Kauai is a typical example.

Under the trees, though, closer to the beach, a different species grows. 

This is manilagrass (Zoysia matrella). It is growing under the trees and creeping onto the rocky beach.

In fact, it even grows right on the beach. The manilagrass is salt tolerant, drought tolerant, and has a finer leaf blade than the seashore paspalum. One might expect to see the seashore paspalum growing closer to the ocean, but in this case, it is the manilagrass that grows right at the water's edge.

For more about these grasses, see:


We have had our water tested and would like a little interpretation

I received an e-mail asking for some help with interpreting an irrigation water test. Since many people may have similar questions, I'll paraphrase the questions here, together with my response.

  1. Is salt the sodium, chloride, and salinity together? Actually, salt on a water test is the total salinity, that is, all the dissolved salts, so it will be sodium and chloride and potassium and nitrate and magnesium and sulfate and calcium and ammonium and so on. And for any irrigation water test, I suggest consulting Dr. Harivandi's Interpreting Turfgrass Irrigation Water Test Results. In fact, this is on my list of Five Articles Every Greenkeeper Should Read. Another great reference is the Irrigation Water Guidelines document from PACE Turf.
  2. What is the difference between SAR and adjusted SAR on a test? The SAR is the number to look at. I disregard adjusted SAR. The adjustment attempts to predict future sodicity problems by considering what chemical reactions may occur in the soil. But it also overestimates the hazard. For a bit more about this, see What's in the water from the University of Nebraska and this abstract from Obear et al..
  3. On our test it shows alkalinity expressed as bicarbonate is 89 mg/L. Is this a problem? No, that is a normal amount of alkalinity. I should add, this is not something that one even needs to check. I spoke about this in a presentation entitled Soil and Water Management: three problems, three solutions. The handout, here, explains how to check the two things that do need to be checked: salinity and sodium hazard.
  4. Do you use ppm or mg/L? These are the same thing. One mg per L is also one part per million.
  5. What does TDS mean? TDS stands for total dissolved solids. It is a measure of the amount of salt in the water. If one would evaporate all the water from one liter, the remaining mass of material is the total dissolved solids, or TDS.

It is important to understand the impact salt in the water can have on the grass, and how that salt should be managed. If it is not managed, the results can be disastrous. 

Water_problems
Salt from the irrigation water has accumulated in the soil, killing seashore paspalum turf on this golf course fairway near Bangkok.

Of course, in many cases there is no problem with the irrigation water. It is still good to know what is in the water, and to be able to interpret the results, because when the turf is good, one doesn't want to damage it in any way.

No_water_problems
The manilagrass and creeping bentgrass at this course near Tokyo are irrigated with water low in salinity and with a low sodium hazard.

And in many cases, there may be a shortage of water for irrigation. In that case, one also needs to know exactly what is in the water, and how it may affect the grass and soil. That is the only way to ensure that this limited resource is used most efficiently.

Water
When a limited amount of water is available for irrigation, it is especially important to know what is in the water and how it may influence the grass and soil.

I'll recommend again, print a copy of Interpreting Turfgrass Irrigation Water Test Results and keep it within easy reach. And the Irrigation Water Guidelines from PACE Turf is another good reference that is useful in understanding test results and identifying (or more likely, eliminating) possible problems.


More about turfgrass at Mauritius

Woods_sv_botanize
Seashore dropseed growing on the beach near Bel Ombre, Mauritius

I visited Mauritius this month for a seminar (report and presentation slides here) and a bit of a botanizing holiday. Mauritius is a fascinating place to study grass. It is one of the Mascarene Islands. If that name sounds familiar, it should -- one of the common names for Zoysia tenuifolia is mascarenegrass. 

One finds a wide range of grasses growing in the wild and as managed turf at Mauritius. I've written about some of the grasses I saw when I visited for the first time a few years ago.

Mascarene
Mascarenegrass produces a dense turf in a highly trafficked park at Gris Gris, Mauritius

The golf courses at Mauritius (there are 8) use bermudagrass (Cynodon), primarily, although 2 of the courses have seashore paspalum (Paspalum vaginatum) everywhere, and 1 more course has seashore paspalum on the greens.

17_anahita
Bermudagrass grows well beside the sea on the 17th hole at Anahita, Mauritius

 One can find seashore paspalum growing in low-lying wet areas at Mauritius. Seashore paspalum is not tolerant of drought, so one does not find it in the wild in areas that do not have a regular supply of water.

 

Paspalum (1)
Seashore paspalum growing at the edge of and into a pond at Belle Mare, Mauritius

The golf courses at Belle Mare are bermudagrass, with some Stenotaphrum secundatum growing in rough, in the shade, and in unmown areas.

Belle_mare
The 17th hole on the Legends course at Belle Mare, Mauritius; Stenotaphrum is growing in the unmown foreground, with bermudagrass on the green and surrounds

The Paradis course is near sea level and has seashore paspalum greens and bermudagrass on tees, fairways, and rough.

Paradis
Talking about different grasses and their management at Paradis Golf Club at Le Morne, Mauritius

There are interesting turf evaluation plots at Paradis. And even more interesting is to observe what grasses are growing, and how they perform, on the course. One can find different types of seashore paspalum on the greens, seashore dropseed growing right beside the lagoon, bermudagrass covering most of the course, Stenotaphrum secundatum in much of the rough, and even some patches of mascarenegrass.

The seashore paspalum performs well on the greens at Paradis, and on the fairways, it makes an excellent turf in the low areas that seem to be at or below sea level, where the bermudagrass does not persist. But on the drier areas of the course, which consists of most of the fairways and rough, on generally sandy soil, the bermudagrass and Stenotaphrum dominate the sward.


Turfgrass Mystery: identifying the underwater grass

This one, I think, will be relatively straightforward. Last week I was at Mauritius. I spoke at a seminar, and I also had a chance to explore the island and to study the grasses growing near the ocean.

Beach_grassI saw this grass growing at nearly every beach, on all sides of the island. It clearly has a high salt tolerance, because at high tide, the ocean water completely inundated some of the plants. I didn't notice salt causing any damage to the grass.

This grass was also observed slightly up from the water line, where the sand and grass were not inundated daily.

It was especially impressive to see this grass, at high tide, completely covered by ocean water.

Sandy

The mystery I would like to solve is this one: what species is this grass?

The answer to this mystery is Sporobolus virginicus, correctly solved by Mark Field:

There are a number of interesting characteristics of this grass that set it apart from two other common grasses (Paspalum vaginatum and Zoysia matrella) found in tropical coastal areas.

  • S. virginicus is adapted to low rainfall and is very drought tolerant with low water requirements
  • S. virginicus is believed to be pest-free
  • Z. matrella is less widespread and one doesn't find it so much growing in sand; Z. matrella is found close to sea level and in saline conditions but usually is anchored onto rocks or other stable surfaces
  • P. vaginatum will not tolerate drought and prefers moist to saturated sites

This fact sheet from the USDA provides details on S. virginicus.

Dr. Brett Morris shared the above photo of S. virginicus growing in it's typical environment, right on the sand near the high tide line, where it will sometimes be inundated with saline water, and sometimes be exposed to extended periods of drought stress.

Sporobolus1The leaves of S. virginicus and P. vaginatum appear very similar, and the best way to tell these grasses apart is to find plants with spikelets. There are profound differences in spikelet morphology between the two species. 

At right is S. virginicus found on the beach at Bel Ombre, Mauritius. Note the spiciform (spikelike) panicle. P. vaginatum, however, has paired racemes, as shown below.

seedhead of salam paspalum vaginatum


What are the best grasses for links golf?

I'm often asked about grasses that will look like fine fescue, or will produce the playability characteristics of fine fescue, in a tropical or subtropical climate in Asia. I've written about this in the January 2013 issue of Golf Course Architecture in an article entitled Achieving the warm season links. And I am motivated to write about this again, because the grasses that are usually chosen for new courses or renovation projects in South China, Southeast Asia, and South Asia, tend to be species that cannot produce those playability characteristics, or, if the grass is to produce the desired surface, it can only be accomplished with high maintenance expenses.

There is a general consensus that fine fescue produces an ideal playing surface for links courses in climates to which these species are adapted. We can find these fescue grasses growing wild in various places, including in rocks beside the sea.

Westman_islands
Fine fescue at Heimaey in Iceland

I find it useful to study which grasses grow wild in a particular area, and to study what type of environment the various grasses are growing in. Fine fescues are stress tolerators, meaning they will live in areas of high stress and low intensity disturbance. Without going into extensive discussion of plant biology, the defining characteristics of stress tolerators are just what one wants in a turfgrass to produce links surfaces.

Festuca_keilir
Fine fescue growing in an environment of high stress and minimal disturbance at Hafnarfjörður, Iceland

When we go to tropical Southeast Asia, we find one grass growing in environments analogous to those in which we find the stress tolerating fine fescue growing in cool climates. This grass is manilagrass (Zoysia matrella).

Ishigaki_manilagrass
Manilagrass growing in an environment of high stress and minimal disturbance at Ishigaki, Japan

Manilagrass is a stress tolerator, with the same desirable characteristics for links surfaces as those found in fine fescue: slow growth rates, long-lived leaves, low nutrient requirements, and superior shade tolerance. In short, manilagrass is the fine fescue of the tropics. 

Ishigaki_zoysia
Manilagrass growing in rocks beside the ocean at Ishigaki, Japan

Even though manilagrass is the grass most similar to fine fescue in its survival strategy, when it comes to new golf courses in South China or Southeast Asia, manilagrass is rarely used. Rather, seashore paspalum (Paspalum vaginatum) or bermudagrass (Cynodon spp.) are the most common grasses planted.

To read more about this topic, see:

Correcting a common misapprehension about seashore paspalum

Grass selection for golf greens and fairways in Asia

Asian Turfgrass Climate Charts, a website with information related to climate and its influence on turfgrass selection and turfgrass performance

Grime's Evidence for the Existence of Three Primary Strategies in Plants and Its Relevance to Ecological and Evolutionary Theory

Grime's Plant Strategies and Vegetation Processes

Universal adaptive strategy theory

Why manilagrass (Zoysia matrella) is the best choice for links-style golfing surfaces in East and Southeast Asia

Manilagrass photo gallery


Does extra potassium improve bermudagrass performance when soil sodium is high?

The short answer is no, as long as sufficient potassium (K) is present in the soil. In another interesting paper from the 2013 International Turfgrass Society Research Conference, Cisar et al. looked at Tifway bermudagrass performance when the soil contained high amounts of sodium (Na).

The results were presented in Beijing and are published in the ITS research journal as Potassium and sodium application effects on soil-test values, and turfgrass quality, clipping yield, and elemental composition of bermudagrass grown in a sand soil. I was especially interested in this research, because I observed Tifway bermudagrass growing in Thailand, and performing well (Figure 1), despite soil Na more than twice the level of soil K.

419_thailand
Figure 1. Tifway bermudagrass grown at the Asian Turfgrass Center's research facility in Thailand performed well despite soil sodium more than twice the amount of soil potassium.
In the experiment of Cisar et al., treatments of sodium chloride were made to establish high levels of soil Na. Over the course of this four-year study, where Na was applied, the soil Na levels were often more than 10x higher than the soil K levels. Where Na was applied, the average soil Na was 246 ppm; where Na was not applied, average soil Na was 47 ppm. 

After a thorough examination of the results, Cisar et al. conclude that:

"The results of this intensive 4-year investigation do not suggest that additional K fertilization is beneficial for bermudagrass quality or clipping yield when elevated soil Na is present."

"Little to no increase in tissue K was observed for K application rates greater than 1.25 g/m2/month." (1.25 g/m2/month is equivalent to 0.25 lb/1000 ft2/month)

"Higher application rates of K fertilization generally did not result in an improvement of bermudagrass quality ratings."

One can use the MLSN guidelines to ensure soil K is kept at an adequate level. Adding more K beyond that level, as this research by Cisar et al. reports, does not seem to confer any benefit.