Page "Soil" Paragraph 13

Most nutrients, with the exception of the lack of nitrogen in desert soils, are present in the soil but may not be available to plants due to extremes of pH.

Most nutrients originate from minerals and are stored in organic material both live and dead and on colloidal particles as ions.

The action of microbes on organic matter and minerals may free nutrients for use, sequester them, or cause their loss from the soil by their volitalization to gasses or by leaching upon their conversion to soluble forms.

Most of the nitrogen available in soils is the result of nitrogen fixation by bacteria.