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ISHS Acta Horticulturae 99: Symposium on Substrates in Horticulture other than Soils In Situ

METHODS USED AT WEST OF SCOTLAND AGRICULTURAL COLLEGE FOR ANALYSES OF LOAMLESS COMPOSTS AND RECOMMENDED LEVELS FOR TOMATOES GROWN UNDER GLASS

Author:   G.C.S. Wilson
Abstract:
Analyses of loamless composts is carried out on three extracts at a 1:2 volume to volume, sample - extractant ratio
  1. distilled water
  2. saturated calcium sulphate
  3. m - ammonium acetate

pH and conductivity are determined on the water extract, nitrogen, phosphate and potash are determined on the filtered calcium sulphate extract and calcium and magnesium on the filtered ammonium acetate extract.

The recommended levels of nutrients for tomatoes grown in a peat substrate are:

nitrogen 500–100 ppm  
phosphate 30–50 ppm (13–22 ppm P)
potash 350–450 ppm (290–374 ppm K)
calcium 1000 ppm  
magnesium 200 ppm  
calcium/magnesium ratio 5:1  
ph 5.5–6.0  
pC 3.0–2.9 (conductivity 1000–1300 micro-mhos,10–13CF)

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