ANALYSIS OF MACRO ELEMENTS AND TRACE-ELEM ENTS IN HORTICULTURAL SUBSTRATES BY THE CACL2 DTPA METHOD .6. MAGNESIUM/

Impatiens-Walleriana-F1-Hybriden were grown in different substrates wi th increasing amounts of Mg to test the suitability of the CaCl2/DTPA- method for estimation Mg in horticultural substrates. 1. Only in wood- based substrates a Mg response occured because peat and peat/clay mixt ures contained enough available Mg. 2. With CaCl2/DTPA about the same amounts of Mg have been extracted as with the standard extraction meth od CaCl2. Contrary with DTPA less Mg and with NH4-acetate more Mg have been found. 3. CaCl2/DTPA soluble Mg contents of substrate and Mg con tents of plants were closely and linearly correlated. 4. In a wood-bas ed substrate with the CaCl2/DTPA method the critical value for Mg defi ciency was about 50 mg Mg/l substrate. 5. To determine Mg the CaCl2/DT PA method is equally suited as the traditional CaCl2 method and saves a separate extraction when horticultural substrates are analyzed for s everal nutrients.