A neutral atom that loses or gains one or more electrons or protons is called an “Ion”. Ions that lose electrons and gain protons have a positive (+) charge, and are called “Cations” (cat-eye-on). An ion that gains electrons, or loses protons will have a Negative (-) charge, and is called an “Anion” (an-eye-on). Ionization can occur in a number of ways, two of which are in water and in soil environments.
Ordinary matter is electrically neutral, and Ions normally exist in groups of Cations and Anions where the sum total of the negative and positive charges is zero. Most of the common Anions are not single atoms, but are groups of atoms called molecules. Common Ion molecules are Sulfates, Carbonates, Phosphates, and Hydroxides. pH is a measure of Hydrogen Ions in a compound, where the higher Hydrogen Ion count, the higher the pH will be. High Hydrogen Ion count is why many acids and bases are corrosive, especially to soft tissue, and will chemically burn human tissue.
The major plant nutrients that occur mainly as negatively charged Anions are Carbon, Nitrogen, Phosphorus and Sulfur. These nutrients form weak acids in water. They are held in soil reserves in the form of complex organic compounds, unlike cations, which bond chemically to soil colloids.
When added to the soil as soluble fertilizers, anion nutrients may be lost because they volatilize into the atmosphere, leach away or revert to more stable insoluble forms. These soluble fertilizers may be acid forming and harmful to soil organisms. When substituted for nutrient sources right in organic matter, they can become an addiction; higher doses will continually be required to replace the nutrients that were previously supplied by the soil’s ecosystem.