soil testing

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Superstorm Sandy, Salt and Sodium
March 5, 2013

Over the past few months I have been getting calls and emails from those affected by Superstorm Sandy; those areas flooded with salt water in particular. It must be a good year for gypsum salesmen in the Tri-State area. Here's the skinny on what to expect and what to do.

Soil samples we have seen have been high in salt and sodium. Salt is the greatest concern from a plant health standpoint and there is no product you can add to counter its effect; just water. A great deal of leaching has probably already occurred over the winter. Now would be a good time to check soluble salts to see if additional leaching through irrigation is necessary.

Sodium is only a problem where it is the predominant cation (positively charged ion) in the soil. If the ratio of sodium is high relative to calcium and magnesium and you have clay in the soil, the sodium causes soil aggregates to break down and disperse, effectively destroying soil structure. A result of this is decreased permeability or drainage. The best management approach to dealing with sodic soils is adding a material high in calcium, usually gypsum. When the calcium in gypsum goes into solution, it replaces the sodium on the cation exchange sites, moving it into the soil solution where it can be leached out. Again, having the ability to leach the soils is important. You have to move the sodium out. A rate of 30 to 50 lbs of gypsum per 1000 square feet should be plenty. Finer grades of gypsum will break down more quickly and are preferred to coarser granular grades.

In sandy soils low in clay (like many coastal areas), gypsum may not be needed at all. In the absence of clay, there isn't much to hold the sodium in place, so it is prone to leaching as well.