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  Eur.J.Hortic.Sci. 80 (4) 190-195 | DOI: 10.17660/eJHS.2015/80.4.7
ISSN 1611-4426 print and 1611-4434 online | © ISHS 2015 | European Journal of Horticultural Science | Original article

Effects of freezing on the physical properties and wettability of highly decomposed peats used as growing media

J.-C. Michel
Agrocampus Ouest, Centre d’Angers, UP EPHor, France

SUMMARY
The influence of freezing on Sphagnum highly decomposed peats was estimated from their physical properties and their wettability measured in relation to the degree of desiccation. The results showed that the physical properties of peats were drastically affected by freezing, particularly improving their water availability and resulting in less, and more reversible, shrinkage after air-drying. However, contact angles measured for frozen or unfrozen peats are very similar. These results seem to indicate that the changes in physical properties are only due to a change in peat structure during freezing and are not a consequence of a change in water affinity. Nevertheless, even if freezing does not affect the wettability of materials, its influence on peat structure contributes to an improvement in their hydric properties.

Keywords contact angle, peat substrate, shrinkage, water repellency, water retention

Significance of this study

What is already known on this subject?

  • The extraction of highly decomposed peat by freezing temperatures during winter is commonly performed by substrate manufacturers. Except for an improvement of agronomic properties, there is no information available on the effect of freezing on the affinity of peat to water.
What are the new findings?
  • This paper showed that freezing modified physical properties of highly decomposed peats by improving air capacity and water availability, however, it had no effect on wettability.
What is the expected impact on horticulture?
  • Since peats began to show a hydrophobic character at water potentials close to those commonly used for irrigation scheduling, the end-users have to be careful in order to avoid poor wettability of both unfrozen and frozen peat.

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E-mail: jean-charles.michel@agrocampus-ouest.fr  

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Received: 10 October 2014 | Revised: 12 June 2014 | Accepted: 23 June 2015 | Published: 23 August 2015 | Available online: 23 August 2015

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