ANALYSIS OF MACRO AND TRACE-ELEMENTS IN H ORTICULTURAL SUBSTRATES BY THE CACL2 DTPA-METHOD .4. PH MEASUREMENT/

An investigation was carried out with substrate samples from a liming experiment as well as with samples from growers to test the suitabilit y of the CaCl2/DTPA-method - recommended for the extraction of nutrien ts in horticultural substrates - for pH measurement. 1. pH values meas ured in CaCl2/DTPA suspension were linearly (r = 0.93) correlated with the values measured in CaCl2 suspension (standard method). 2. pH valu es measured in CaCl2/DTPA suspension were on average about one pH unit lower than the values of the 0.01 M CaCl2 method. 3. Tomato plants gr ew normally within a pH range between 4.2 and 5.2, measured in CaCl2/D TPA suspension. 4. In principle a pH determination in CaCl2/DTPA suspe nsion is possible and leads to a further rationalization of the analys is of horticultural substrates.