exists no in-situ salinity probe that can distinguish between the different ions that may be
present.
When salts such as sodium chloride are in their solid form, they exist as crystals. Within the salt
crystal, the sodium and the chorine atoms are joined together in what is called an ionic chemical
bond. An ionic chemical bond holds the atoms tightly together because the sodium atom will
give up an electron to the chlorine thus ionizing the atoms. If an atom like sodium gives up an
electron, it is said to be a positively charged ion (also called a cation). If an atom such as chlorine
receives an electron, it is said to be a negatively charged ion (also called an anion and is given
the suffix ide, like chloride). The sodium and the chloride ions comfortably arrange themselves
into a stacked like configuration called a crystal lattice. The sodium chloride crystal lattice has a
zero net charge.
Figure [5.3] The crystal lattice model of sodium chloride. The larger spheres are chloride anions.
Water will dissolve the sodium chloride crystal lattice and physically separate the two ions. Once
in solution, the sodium ion and the chloride ion will float around in the solution separately and
randomly.
This is generally true for all inorganic salts. Once in a solution, the ions will float apart and
become two separate species dissolved in the water. Typical, charged ions exist separately in a
solution. If the water dries up, the cations and the anions will find each other and fuse back into a
crystal lattice with a zero net charge.
5.3.3 Cation Exchange and Agriculture – Reclaiming Salt Affected
Land
In situ soil electrical conductivity monitoring is very important in agriculture because the salinity
levels in soil moisture can have dramatic effects on crop health and yields.
Agricultural soils over time may become sodic or saline and this may dramatically effect the
health and yields of the crops. There are techniques that can remove the sodium to improve soil
quality and increase crop production. The Stevens Hydra Probe can be an invaluable tool for
monitoring the progress of saline soil reclamation.
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