More on the effects of excessive sodium

An excess of sodium can decrease the soil's permeability — its ability to readily conduct water and air. It can also decrease the soil's tilth — its ability to cluster into easily crumbled masses of particles. Increasingly slow penetration of water into a soil is one sign that the soil contains excessive sodium — a condition that scientists describe as sodic. A white or black crust on the soil's surface is another symptom of sodic soil.

Irrigating with recycled water sometimes causes such a problem. This is because recycled water tends to contain a somewhat elevated amount of sodium and, at the same time, relatively low concentrations of salt. Such a combination of conditions is more likely to cause sodic soil.

At what point does the salt in irrigation water become harmful to plants? It all depends on a combination of the following:

• what's in the water, namely, the total amount of salt, as well as the types and concentrations of ions;
• what type, species, and age of plant is involved;
• what types of soil and climate are involved; and
• how well all of the above are taken into account to manage a particular landscape.

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