ISHS Acta Horticulturae 294: II Symposium on Horticultural Substrates and their Analysis, XXIII IHC
THE RELATIONSHIP OF OXYGEN DIFFUSION RATE TO THE AIR-FILLED POROSITY OF POTTING SUBSTRATES |
| Author: | A.C. Bunt |
| Abstract:
Potting mixtures having a wide range of physical properties were prepared from Canadian sphagnum peat, fine or coarse grade sands, perlite and a mixture of redwood bark and sawdust. Using containers holding 14 cm depth of substrate, oxygen diffusion rate (ODR, g O2 x 10-8 cm-2 min-1) profiles were determined for 13 substrates with a platinum micro-electrode, the results being corrected for a constant effective voltage (-0.65 V). An integrated ODR value was computed for each substrate and these were correlated with the air-filled porosity (AFP, %) values for the containers giving the following relationship which accounted for 91.3% of the variance: ODR = 10 + AFP1.85. The AFP values of potting substrates can therefore be used to estimate the mean ODR, eg. at an AFP of 10% the ODR will be 80g g O2 x 10-8 cm-2 min-1. ODR profiles of a 100% peat substrates showed that irrigation caused a shallow layer of peat, about 2 cm below the surface, to become dispersed, resulting in this layer having a lower ODR than the peat immediately above and below it. | |
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