Magnesium in forage plants. II. Magnesium distribution in grasses and clovers

Abstract

1. A procedure for fractionating the magnesium in fresh herbage into acetone-soluble, watersoluble and insoluble magnesium fractions is described.2. Magnesium soluble in Analar acetone is shown to be virtually identical to chlorophyll magnesium, and generally represents less than 10% of the total magnesium.3. Water-soluble material represents about 25% of the total dry matter, but contains more than 50% of the total magnesium when the herbage contains 0·2% or more Mg in the dry matter.4. The fibrous material, which is soluble neither in acetone nor water, constitutes about two-thirds of the total dry matter, but has only about onethird of the total magnesium associated with it.5. Highly significant correlations were found between total magnesium content and each of the three fractions, but regression coefficients showed that variations in total magnesium were largely reflected in the water-soluble fraction, the chlorophyll and fibre magnesium being affected to a much smaller degree.6. Attention is drawn to the fact that at levels of pasture magnesium at which hypomagnesaemic tetany occurs in ruminants, water-soluble magnesium ceases to be the largest fraction and may be only about one-third of the total.