ABSTRACT
Rocks and minerals, which have been in existence at least four billion years, usually contain a higher percentage of magnesium than do soils; this reflects the loss of magnesium during weathering. During weathering, magnesium may be precipitated in clay minerals, a process which plays a significant role in governing the solubility of magnesium in soil. Magnesium is more abundant in the parts of a plant that are concerned with vital processes, such as seed and foliage, than in roots and stems. The lack of magnesium in early spring grass may result in so-called grass tetany in animals grazing on young grass in soils low in available magnesium or where the soil solution contains a high concentration of the stronger cations which may limit absorption of the weaker magnesium ion by certain plants. Magnesium is a factor in nitrogen fixation by nodule bacteria of legumes. In its absence a rather characteristic chlorosis develops in green plants.
