Written by Mike Hamilton, CCA & President of Turf Dietitian
Understanding Sodium’s Function
Even though sodium is an essential element, we rarely think of it as part of our nutritional programs. Sodium is typically that evil nutrient that quickly becomes destructive to plants and soil structure. Because of osmotic pressure, moderate levels of sodium can suck moisture and nutrients in or out of plants, shrink roots, and diminish many of metabolic functions of a healthy plant.
Sodium replaces other nutrients on soil exchange sites and within the plant, especially potassium. Sodium and potassium are similar in size, are both carried into the plant through diffusion, and perform many of the same functions; mainly that of respiration and transpiration. Therefore, potassium will usually be the essential replacement nutrient when managing sodium.
High sodium levels on turfgrass are mostly caused by high sodium levels in water sources, but can also be caused simply by natural sodium deposits in the soil.
We work with hundreds of golf courses across the United States, and over three-quarters of them have sodium issues serious enough to warrant frequent monitoring and management. Most of the more serious problems we see are within 100 miles of an ocean or in the desert Southwest. However, we do see courses in those extreme zones that don’t have sodium issues, and courses in sodium free environments that have issues. Therefore, never assume you do or don’t have a sodium issue simply because of your location. Depend on testing to determine the challenges and establish a management strategy based on the data.
Inland sodium problems don’t tend to fluctuate as much as coastal courses, but are harder to manage because of the lack of rainfall. Sodium levels on coastal soils can fluctuate frequently due to seasonal rains, tropical storms, solar tides, high winds blowing off the ocean, elevated ground water levels, and osmosis movement. Consequently, your management programs should change to compensate for those instabilities.
Courses with moderate to extreme sodium levels will need to repeatedly manage the concentrations in the rootzone. If you don’t. you will be risking the health of the turf and soil, especially during periods of environmental stress. It’s also wise to test soil, water, and plant tissue frequently to help determine frequency and level of control measures. The more serious the challenge, the more you should test and adjust your procedures.
If the golf course you manage is one of those that has low levels of sodium in your water source and soil, count your blessings, but don’t assume it will always be that way. Although you won’t need to manage sodium as intensely as courses with high levels, you should still work on sodium ratio balance with other major cations. One example: if sodium is low, but potassium is lower; you have a sodium issue. Sodium will replace potassium in the plant which will affect respiration and transpiration.
We have a handful of golf courses (mostly in the mountains and the Northwest) in which the soils are almost deficient in sodium. Not many of those Superintendents apply sodium, but probably should.
Developing a sodium management program
Twenty years ago, managing high levels of sodium in plants and soils was usually attempted by applying gypsum a few times per year. However, as the demands for faster, smoother, greens grew, so did the necessity to develop more efficient and precise techniques.
In order to develop an effective sodium management program many factors must be considered. Let’s take a good look at most of those factors:
1. Determine the seriousness of the problem.
a. Levels of sodium in the soil and water
i. Levels in soil and water can vary drastically based on soil structure.
ii. Should you treat the soil or the water.
b. Ratios of sodium with other cations
i. Extremely important for managing healthy turf and soil.
c. Soil texture-soil density
i. The finer the soil partials the harder it is to manage problems.
d. Soil Structure
i. The better the soil the easier it is to manage the problem.
e. Percentage organic matter
i. The higher the OM the harder it is to correct problems.
f. Water infiltration rate
i. The lower the IR the harder it is to correct problems.
g. Percentage of air to water pore space
i. The higher the oxygen pores the easier it is to manage the problem.
h. Seasonal sodium impacts
i. Dilution of water from seasonal rain fall can temporarily improve water quality.
i. Weather impacts
i. Hurricanes, tropical storms, and string winds off oceans can dramatically worsen sodium issues
j. Plant tolerance
i. Sodium tolerant turf lessens the impact of high sodium soils.
k. Anion ratios
i. Determines efficiency of products used to manage high sodium soils.
2. Take soil, water and tissue samples.
a. Soil test will provide data to determine soil structure, sodium levels in soil reserve, and soil solution.
i. Data from soil structure will indicate the degree of difficulty in managing sodium.
The data above shows good soil structure. Low OM and SI makes it easier to manage sodium because you are assured that water will move through the soil quickly, allowing sodium to be flushed. Routine flushing will be an efficient means to push sodium out of the rootzone. Low CEC shows that less K, Ca, and Mg will need to be applied to replace sodium on the exchange sites.
The data above shows poor soil structure. High OM and SI makes it more difficult to manage sodium, because poorly structured soils hold water. If you can’t push the water through the soil, sodium will only accumulate. Turf grown in saturated soils are more prone to sodium impairment, due to lack of oxygen and root deterioration. Flushing becomes more difficult because it necessitates more water and time to achieve gravitational flow. High CEC show higher amounts of K, Ca, and Mg will be required to displace sodium and establish balanced ratios. If the greens have no sub-surface drainage, it may be unfeasible to achieve a gravitational flush.
b. Ratios of sodium to other major cations in soil reserve
If you are managing soils that have persistent sodium problems, then sodium ratios to other base cations will be essential data for you to identify. Flushing is a great tool to cleanse the rootzone exchange sites, but it’s only temporary relief. After three or four irrigation cycles the sodium concentrations will begin to increase again. Making a bulk application of calcium, potassium, or magnesium after the flush will increase the time intervals between the flush.
It’s my opinion that target ranges on a soil report are useless information when correcting sodium ratios. If you prescribe to that theory, and don’t apply a nutrient when it shows up high, you will be unable to correct the sodium ratio.
Actual Calcium to Sodium is 10 to 1.
Actual Magnesium to Sodium is 1.3 to 1
Actual Potassium to Sodium is 1 to 1.
Ideal Calcium to Sodium range is 47 to 1
Ideal Magnesium to Sodium range is 8.5 to 1
Ideal Potassium to Sodium range is 2 to 1
Look at the ratios between calcium, magnesium, and potassium with sodium from the data above. The data shows calcium and magnesium are high in soil reserve. Yet, when you look deeper into the data it shows they are very low in ratio to sodium. Because the soil is getting a constant feed of excess sodium with each irrigation event, the only way you will correct the sodium ratios is to ignore the target ranges. What’s missing from the data above is this course has high organic matter and a saturation index. Since this course has poor soil structure, magnesium will likely make the problem worse.
I always stress caution when applying bulk rates of magnesium. High levels of magnesium will damage soil structure and cause waterlogged soils because of its small size.
The more serious the sodium challenge the more frequently you should test your water source. Water testing not only gives you an indication of where the nutrients in the soil are coming from, it also allows you to adjust based on the most current conditions. Your water source won’t likely change from day to day, but it will change from season to season and after large rain events. Typically, water is cleaner and more balanced during the rainy season, and at its worst during periods of drought. Seasonal changes in water quality can change the intensity and strategy of your management program.
The ratios for major cations on the water report ideally should be the same as soil ideals, and usually are if the soil structure is good. However, many times soil conditions are worse than the water quality.
As you can see from the water data blow, sodium is extremely high. If your water report looks like this, then sodium management will likely be your main challenge.
The question I get the most from superintendents is, “Should I amend the water or the soil?” My opinion is that treating the soil is the best method to manage sodium in most cases, because the soil has holding capacity. Treating water is a temporary fix, it’s expensive and if not constantly monitored, can cause as many problems as it corrects.
A lot of golf courses treat water with different forms of acid. But acid products aren’t really intended to manage sodium. Acid products are used to strip nutrients from soil colloids, and to help mineralize chemical compounds in the soil. I’m a big fan of using weaker acid products in a flushing and replace program because of its ability to free up exchange sites. However, I believe frequent applications of strong acids has the potential to create long term toxicity problems.
The general rule of thumb for determining whether acid injection is a practical tool for your golf course is based on absorption ratios. If the adjusted sodium ratio is 2 units higher than the sodium absorption ratio, then you will most likely see benefits. However, keep in mind if the adjusted ratio is only 2 units higher, the requirements will be less, and the intervals of use will be greater than if that number is higher.
3. Determine what type of sodium soil you have on your property. There are three types of high sodium soils: saline, saline-sodic and sodic. All three have their own unique characteristics, and all require a different management program.
a. Saline Soil
i. Contain ample amounts of soluble salts to injure plants.
ii. Typically have large enough amounts of calcium and magnesium to offset sodium accumulations.
iii. Have EC of 4 or higher
iv. Typically have high levels of sulfate and chlorides in soil solution.
b. Saline-Sodic Soil
i. Higher concentrations of sodium salts in ratio to calcium and magnesium
ii. Soils typically have an EC of less than 4
iii. Exchangeable levels of sodium higher than 15%
iv. pH’s below 8.5
c. Sodic Soil
i. pH’s higher than 8.5
ii. Extremely high exchangeable sodium
iii. The soil is sticky when wet but forms hard clods and crusts upon drying.
iv. Low water and air permeability.
4. Measure electro conductivity daily and chart.
a. Valuable data to adjust your program frequently and anticipate environmental changes.
5. Measure electro conductivity at various depths 2”, 4”, and 6”
a. Measuring at various depths will provide data for flushing depth and frequency.
b. Low to slightly salinity track monthly
c. Moderate and higher salinity track weekly.
d. GPS moisture meters make collecting and logging this data easy.
Methods to manage sodium
Flushing is one of the most valuable tools for managing sodium, but it’s only a temporary mitigation of sodium pressure.
Flushing can be accomplished by applying enough water to achieve gravitational flow through the soil profile. Flushes are better accomplished when calcium-based products, organic acids, and wetting agents are used in conjunction with the purge.
Flushing accomplishes four things:
- It helps to strip nutrients off occupied soil colloids.
- It pushes the released nutrients through the profile with the water flow.
- It pulls oxygen down into the soil pores. The oxygen that’s pulled into the soil will enhance root growth, which will in turn improve soil structure.
- It increases microbial populations.
The goal of the flush is to reduce the amount of sodium occupying the exchange sites, then immediately replace it with calcium, potassium, or magnesium. By applying soluble forms of nutrients immediately after the flush, you are attempting to change the sodium ratios on the cation exchange sites to enhance a more balanced plant uptake of the base cations.
Soil data will give the information you need to know what nutrients to replace, at what ratio they need to be applied, and the source of product that will be most efficient.
When I look at the data below, I see the need to apply calcium and potassium to balance the CBS and use them in the carbonate form to enhance efficiency.
If you have good soil structure, the flushes will be quicker, less frequent and require less water to achieve a gravitational flush. For flushing to work the way it is designed, you must get a complete flush of water through the entire profile. If you don’t get a complete flush, you are likely to have little effect on changing sodium ratios and may even make the ratios worse.
For a true flush to occur, there must be water flowing through the drain tile at the end of the process. The process starts by filling the greens well to field capacity, then continue applying water until you get a steady flow through the tile. If your greens have moderate to bad soil structure, it will require more water to flush and will require cycle soak techniques to prevent run off.
I have flushed old greens that had never been flushed before that have required 4 to 5 hour’s run time per head. After the first flush those same greens flushed with 45 minutes of run time. I’ve also had old greens with no sub-surface drainage that I couldn’t flush, so not every course can use flushing as a tool. The bottom line is, if you have greens that can’t be flushed, they should have been rebuilt years ago.
Bulk applications to balance soil is a simple strategy. Use soil date to determine how acute the problem is, determine what nutrients to apply, determine the best source of product to use, then apply.
If you have sandy soils with good structure and low organic matter it will be easier to maintain and adjust soil balance. However, if you have poor soil structure, it may be financially unachievable to make a big impact through bulk applications.
We work with golf courses that have fairways and greens that are more than 100 years old. Many of those courses have heavy organic matter, on top of dense clay soils. These types of soils have a tremendous holding capacity and will require tens of thousands of pounds of each individual nutrient per acre foot to make a big difference. I don’t know of any golf course that has that type of budget. Yet, doing nothing is not a good answer either. If you have fundamental challenges with sodium, do as much as you can afford. Ag grade fertilizers consist of coarser grade particles, they move slowly through the soil profile, and can take a few years to completely mineralize. After a few years of consistent application, you will start making positive gains in the rootzone.
Too many times, I see a superintendent trying to amend newly constructed greens after the fact. The best time to amend new greens is when the mix is blended. You can add large amounts of nutrient, adjust ratios, and balance the entire column of soil. The number one reason I get for not blending nutrients in early stages of construction, is cost. In my opinion, it’s better to cut costs in another part of the golf course than to not blend the nutrients.
Any extra expense for amendments on greens in the early stages will only add to the longevity of the greens.
Improving Soil Structure
The success of any crop starts with soil structure. How do you improve soil structure? Oxygen! But, what can you do to improve soil structure if you have soils like mentioned above? Oxygen!
Farmers have a great advantage over golf courses, because they plow 12 to 18 inches of soil once or twice per year. Plowing increases air holding capacity, which infuses massive amounts of oxygen in the soil. Soil oxygen increases microbial populations, which further improve soil structure and soil productivity.
Superintendents aerify when golfers let them. Aerification is better than nothing, but only infuses small amounts of oxygen into the soil. Aerification of poorly structured soils rarely see a net gain of oxygen space in a soil profile.
The more aggressive you get with your aerifacation and top-dressing programs the better product you’re going to produce. The closer you can get to plowing your poorly structured soils, the easier it will be to improve conditions. Every year at the GCSAA show, I see new types of more aggressive equipment that’s aimed at deeply agitating soil.
Alternative Water Sources
Alternative water sources are rarely an option, but if you can find a cleaner water source it will payoff in the long run. I work with several courses with poor quality water, that use city water on greens, and it makes a big difference.
When soil and water are dominated by excessive amounts of sodium, very little in the plant is functioning correctly. At that point it may be better to bypass the soil and apply plant absorbed nutrients directly to the foliage. Spraying nutrients or injecting nutrients through the irrigation system may be the best option to feed the plant.
All elements can be toxic and can wreak havoc on both soil and plants. However, none wreak more havoc or require more attention than sodium.
There are many times we are called out to look at sick turf. In almost every case, the superintendent is at the point in which they have thrown the kitchen sink at the problem. Most of the time the final stage of the decline is due to pest, nutrition, or water problems. Unfortunately, rarely is sodium taken into consideration as the precursor.
If you have sodium issues, my advice is to develop a detailed management plan. Of course if you would like an individualized approach at developing a plan, give Turf Dietitian a call, we’d love to help.