IRON AVAILABILITY IN PEAT SUBSTRATES AS ASSESSED BY WATER, CALCIUM-CHLORIDE, AMMONIUM ACETATE, DTPA AND CALCIUM-CHLORIDE DTPA

An experiment was conducted to find out which extractant for a peat su bstrate gave the best prediction of iron (Fe) uptake by the plant. Iro n was added in four levels (including zero) to peat in the form of eit her EDTA or sulphate, at two pH levels. Iron from the peat was extract ed by water, 0.01M CaCl2, 0.5M NH4OAc, 0.O02M DTPA and 0.01M CaCl2/0.0 02M DTPA. The test plant was chrysanthemum. Iron in the plant was dete rmined by total analysis and by o-phenantroline and HCl-extraction. Ir on additions and pH differences resulted in large differences in Fe co ntent in the peat. Tron contents in the plant were hardly influenced b y the treatments. There were poor correlations between Fe in the peat by the various extractants and Fe in the plant. This is probably relat ed to the very small differences in Fe contents in the plant. These sm all differences could have been caused by the fact that at the low gro wing rate of the plants during the experiment (winter), also low Fe co ncentrations in the substrate were enough for the plant.