Magnesium-organic matter complexes

Iron oxide may also increase the beneficial effects of organic matter (Chesters et al., 1957). McIntyre (1956) concluded from studies of soils in South Australia that the chief influence on the structure of these soils is iron acting through the medium of an iron-organic matter complex. In semi-arid soils calcium and magnesium carbonates may also act as cements. These materials are carried in the soil percolate and a portion is deposited on aggregates, or may form hardpans at lower levels. 

The Analytical Methods Committee of the S,A,C. has described a method for the determination of traces of magnesium, based on the method of Hunter. In this method, after destruction of organic matter, the magnesium is complexed with Titan Yellow and the excess dye is extracted from the reaction mixture and determined spectrophotometrically. The method is generally applicable but zinc, if present in quantities greater than 10 per cent of the magnesium content, interferes and should be removed. Aluminium, cadmium, cobalt and nickel interfere also. The recommended procedure is as follows ... 

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