All but one of the essential elements is absorbed by plants from either soil solutions or nutrient solutions as either a cation, a positively-charged ion, or an anion, a negatively-charged ion. Cations and anions may differ not only in the sign of the ionic charge (positive/negative), but also its magnitude (1, 2, or 3).
In the table below, the essential elements are listed in their approximate order of critical concentrations, from greatest to least, from top to bottom. Interestingly, several elements are absorbed as oxyanions, ions composed of the element surrounded by three or four oxygen atoms, giving a net negative charge. Also of interest is the fact that several elements are taken up in different forms.
From this table, a number of points can be made:
This page was last modified by Phillip Barak, Univ. of Wisconsin, on 2 Feb 1999. All rights reserved.