ISHS Acta Horticulturae 548: International Symposium on Growing Media and Hydroponics
RELATIONSHIP BETWEEN THE 1:1.5 WATER EXTRACT AND CaCl2/DTPA(CAT) EXTRACT IN VARIOUS GROWING SUBSTRATES |
| Author: | M. Prasad |
| Keywords: | water extract, CaCl2/DTPA extract, cations, anions, white peat, black peat, cocopeat, bark, woodfibre, critical values |
| Abstract:
The objective of this investigation to study the relationship between the 1:1.5 water volume extract and 1:5 volume CaCl2/DTPA extract (CAT), so that desirable values which are widely available for a wide range of crops values for the 1:1.5 water extract of crops could be converted to the 1:5 CAT method which is a relatively new method and has a dearth of desirable values. A 1:1.5 CAT volume extract was also included in this study. It was felt that the lower ratio of substrate to extract would be useful where a coarse material was being used and a larger volume of sample would be desirable to get a representative sample. Five substrates, namely white peat, black peat, composted spruce bark, woodfibre and cocopeat was used in this study. These materials received lime and five rates of a complete fertilizer. After incubation they were extracted by the three methods. There was a very good relationship between the water extract and the CAT extract as regards nitrate and phosphorus, regardless of the growing substrates used. However, the 1:5 CAT extract tended to give slightly higher value than the 1:1.5 CAT extract. The relationship between the water extract and the CAT extracts was poorer for the cations, ammonium and potassium. This poor relationship was primarily due to poor relationship between the water and CAT methods on growing substrates which are buffered such as bark, cocopeat and black peat. Here the relationship was often not linear and recovery of nutrients with water was much less than the CAT methods especially at the low rates. Thus it is not possible to convert desirable values from the 1:1.5 water extract method to the CAT method for cations using a regression equation that is valid for all types of growing substrates but such an equation will be valid for the anions for all types of growing substrates. | |
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