Whenever we think of salts we automatically think of table salt, something we see every day. We know what it looks like and we even know it by taste. It’s only one of a wide family of compounds that we call ionic compounds that come about when an acid meets a base.
For example, if you introduce hydrochloric acid (common stomach acid) to lye (sodium hydroxide) the result is sodium chloride (table salt) and water. The sodium half of the molecule has a strong positive charge and is called the cation. On the other hand, the chloride is negative. Once the two are bolted together, the resulting sodium chloride molecule is neutral.
This is a relatively simple example, but it illustrates the point. Farmers face a number of different salts, some chemically simple and some more complex.
Another salt farmers know well is an isopropylammonium salt — an acid molecule bound to a salt for the purpose of packaging and handling. It’s more commonly known as glyphosate.
Magnesium sulfate, also known as Epsom salts, are fairly common in bath salts and are used in a number of medical treatments. It’s also one of the most common salts found in prairie salt clays and, since it dissolves easily in water, it’s one of the most serious causes of soil salinity.
Salt and water
Most of our crop species don’t tolerate soil salts particularly well. This is because salt interferes with the plant’s uptake of water. Water is precious in a dry environment and a plant that can’t get water is a dead plant. Saline groundwater messes with the “water potential” of the environment.
Simply put, water likes to move to where the salts are. If the water is pure and it’s sitting next to a plant cell with “solutes” dissolved in it, that water wants to move to where the solutes are. The “water potential” is greater in the cell so the water crosses the cell wall and moves in. If the water in the surrounding soil has more solutes than the cell, the water potential is the other way and it moves out of the cell and into the soil. The cell dies.
Oddly enough, magnesium sulfate may also be used as a fertilizer on land that’s deficient in either magnesium or sulfur and it may also be used with crops that are big users of these elements such as potatoes or tomatoes. Still, too much of a good thing is toxic. †