Salinity Management for Sandy Soils

Salt burn  on almond.

Salt burn on almond.

AUTHORS NOTE: The following article discusses salinity management considerations for SANDY SOILS (e.g. sands, loamy sands). A follow up post will be made for finer texture soils (loams, silts, and clays). For the most part, this article describes issues with the EAST SIDE of the San Joaquin Valley. NOT ALL SOILS ARE THE SAME. Please note that the following guidelines may need site-specific adjustments.

During low rainfall years, salt burn often shows up in sandy soils. This salt burn is a combination of accumulation of sodium within the soil, the use of well water, and the low exchange capacity of the soil.

Starting with the soil, we often use the term cation exchange capacity (CEC) which is the amount of cations (positive charged ions like sodium, magnesium, calcium, potassium, etc.) that can bind to the soil particle surface. In the sandier areas on the east side of the San Joaquin Valley, CEC values can be quite low, with values less than 10 meq/100 g of soil. To put that in perspective, sandy loams are in the teens through 20s, silts and clays are in the 30s to 40s. This value is important as it indicates the amount of cations the soil particles can hold. The higher the CEC, the more cations that stick to the soil, preventing them from entering the soil water (soil water is the amount of water that is held between soil particles – it is what the tree drinks), reducing exposure to the roots of the tree. Regardless of the CEC, once the soil is saturated with cations, the excess will stay within the soil water. As the soil salinity increases, the tree’s roots have a greater exposure impacting them by affecting the osmotic movement of water (e.g. essentially making the tree work harder for water) and  eventual toxicity.

In most sandy areas, interestingly enough, salinity levels within the water are often low.  ECs commonly range from 0.5 – 1.0 dS/m, a value in which many would think sodium uptake issues would not occur. This would be true if accumulated salts are flushed out of the rootzone. Salts accumulate in the rootzone due to the ability for the plant’s roots to exclude them. For the most part, roots exclude between 95-99% of the sodium applied. As water is applied, the tree sucks up the water leaving the sodium behind. As subsequent irrigations occur, the sodium begins to accumulate. After multiple irrigation cycles (e.g. once a week through the summer is about 20 irrigation cycles), the soil will gradually become saltier than the water applied. At some point, the concentration of sodium exceeds the tree’s ability to exclude them. The sodium is then picked up by the tree, moves to the leaves, and burn occurs.

The combination of the accumulation of sodium with the low cation exchange capacity is why sodium toxicity occurs rapidly on sandy soils, especially when there are no winter rains or irrigation to help leach the sodium.  The good news is that within sandy soils, sodium can leach almost as fast as it has accumulated. This can be done by emulating rain through winter irrigations. If possible, an application of at least 4-6 inches of water before the end of November. This will fill the soil profile (check to be sure by probing to 5 feet). If over a half inch of rain occurs before then, it can be subtracted from the targeted total. This water should be applied in 18-24 hour shots. After an application, wait 4-5 days, and apply another irrigation until  the targeted total is reached.

After the soil profile is filled, another 4-6 inches of water will be needed. This can fall as rain or irrigation. After the soil profile is filled, any subsequent rains can count as leaching water. The leaching process should be completed by mid-January. This means that if Jan 1st comes around and no rain has fallen, winter irrigations following the episodic patterns as described above should begin. Do not wait until mid-Feb. Root expansion occurs in mid-January, and irrigating later than this could create anaerobic conditions, which kill the newly developed fine feeder roots.

Applications of calcium can help with the leaching process. Calcium can help displace the sodium from the soil’s charge sites. Although helpful, they are not required. I would rather see the money spent on pump time than on gyp as water is more critical than calcium at this point. If applying gypsum, make sure to apply potassium AFTER the gyp applications. Potassium is a single charged like sodium and will also flush out of the system.

On sandy soils, I have seen orchards recover within two-three years as it takes time for the trees to “flush” out the accumulated salts. Usually, the trees will express symptoms in the following year, but they are reduced. In the subsequent years, the damage will be less prevalent and the tree will respond with increasing yields.

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9 thoughts on “Salinity Management for Sandy Soils

  1. Have you done any work with soil surfactants? We have seen a benefits when using for increasing water penetration, for difficult soils, in season. What about helping to leach salts in the fall and winter?


    1. Ken,
      To answer your first question – not really, simply due to the costs associated with the use of surfactants and the effectiveness of calcium amendments.

      As you stated surfactants help water infiltration by reducing the surface tension of the water, which helps it mitigate the chemical sealing that has occurred in the top few millimeters of soil. This could help with leaching as it would help increase the rate of water movement into the soil, but I am unsure if it is superior to other soil amendments that attempt to reduce soil sealing (e.g. calcium containing products). I would think it would be better to see a program that is heavy with gyp have no effect before I would switch to surfactants. The problem with gyp, however, is that it may take several applications before the effect is visible.

      Keep in mind that the SAR must be in balance in order to maintain rates of infiltration.

      David


  2. Soil surfactants are much easier to apply than gypsum unless you have a soil solution or other comparable machine. Soil surfactants seem to work much faster than gypsum, we see a response much quicker, in water penetration and a responses in the trees. We are not just talking top millimeters of soil, but infiltration below a foot or two.
    Cost wise they are a little more expensive but used with gypsum seems to give use better bang for the buck. There are many brands out there. I am not sure what the differences in all of the proprietary brands.


    1. Ken, I fixed my first comment to accurately respond to your questions (my first statement was answer to your first question – sorry for the confusion). I agree with your comments on surfactants. They tend to work faster, but the effect is not as long lasting as if the soil and water are properly amended. As you said, they provide a greater benefit when used in combination with other techniques to mitigate infiltration, but are expensive.

      By the way, here is a great reference for managing infiltration issues: http://fruitsandnuts.ucdavis.edu/files/73694.pdf

      I should also add that sandy soils, which this article is discussing, rarely have issues with infiltration rates.
      David


  3. Felicitaciones por los trabajos y comentarios.

    Trabajo con surfactantes y es una herramienta real, practica, fácil de usar y 100% efectiva

    Manejar sequías y sus consecuencias no es ni fácil ni barato, pero mucho peor es perder los huertos de años


    1. Muchas gracias para las comentarios.

      Surfactants do have a use, but are part of the solution to a much more complicated issues. Infiltration issues have been a major issue facing irrigated agriculture for over 100 years. In micro-/drip-irrigated systems, these problems can be much worse due to the amount of water applied to the area of soil. More information on the research and how it applies to orchard soils can be found here: http://fruitsandnuts.ucdavis.edu/files/73694.pdf

      David


  4. Pingback: Salinity Management for Fine Textured Soils - The Almond Doctor

  5. David, it seems that a few growers have used soil surfactants and they see a real value and great return on investment. Do you have any interest in testing soil surfactants? You comment that “Surfactants do have a use, but are part of the solution to a much more complicated issues”. Can you elaborate on that please? I believe gypsum is a good long term soil amendment, but we the technology is offering growers easy to use and effective tool to battle surface tension and most important improve water use (SAFE WATER) and surprisingly to growers IMPROVE yield and quality of fruits due to enhanced movement of water into the soil- both lateral and vertical , stimulating the root system to use the nutrients efficiently. Best regards,


    1. Elena,
      I dont know how to elaborate more than that comment. Surfactants alone wont solve a salinity problem, neither will gypsum or water, they will assist and must be part of a long term program. The only way to reduce salinity issues is to remove salts from the rootzone. In almonds, this is done with winter leaching programs utilizing amendments and water to help “flush” toxic salts. Salts can be also removed with crop load, but this usually is not possible due to the amount being applied v/s removed.

      There has been ample testing of surfactants in the past. They have been shown to assist in the above mentioned ways. What questions do you wish to answer? Are they any different from the ones asked before?
      David


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