MULTIPLE APPLICATIONS OF FEDTPA OR DTPA ON MICRONUTRIENT EXTRACTION AND POTENTIAL AVAILABILITY FROM PEAT-BASED MEDIUM

The chelate, DTPA, has been shown to be an effective extraction agent for the micronutrients from peat-based soilless media. Multiple applic ations of 2 mM DTPA extracted 95 ppm iron (Fe) after one week and then declined to 16 ppm Fe while 0.2 mM DTPA extracted Fe which increased to 16 ppm after three weeks. Leachate Fe concentrations from 0.02 mM D TPA and 0.02 mM FeDTPA were similar, increasing from 1 to 2 ppm. Leach ate Fe concentrations from 0.2 mM FeDTPA increased from 7 to 14 ppm, h owever, 0.2 mM DTPA decreased from 9 to 3 ppm. The 0 DTPA treatment ha d a constant 0.1 ppm Fe in the leachates. Manganese (Mn) was rapidly e xtracted from the medium. Leachate concentration of both copper (Cu) a nd zinc (Zn) increased slightly above applied concentrations. There we re no differences in dry weight or total micronutrient content among g eranium (Pelargonium x hortorum 'Aurora') grown with either DTPA or Fe DTPA treatments 0.2 mM and below.