FORESTRY UPDATE by Gary Allen Burns 8-31

The nutrients in the soil that the plant roots take up are in the soil as ions. Ions are charged atoms or groups of atoms. Most metals form positively charged ions, called cations. Cations include Ca2+, K+, Na+, and Mg2+. Clay particles and humus both may have an excess of negative charges on their colloidal surfaces. Cations can bind to this surface, preventing being leached by the soil water.

The bond is weak and these cations can be replaced by other cations and be released into the soil solution, available for plant uptake.

Negatively charged ions called anions are also found in the soil. The principle anions found in the soil are NO3-, SO42-, HCO3-, and OH-. Anions don’t attach to clay particles and therefore leach out of the soil more rapidly than cations. Leached nitrate ions, in particular, have polluted water systems.

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