TITLE:
Effect of Air Content on the Oxygen Diffusion Coefficient of Growing Media
AUTHORS:
Dominik Schmitz, Ruediger Anlauf, Peter Rehrmann
KEYWORDS:
Gas Diffusivity; Pore Tortuosity; Air Capacity; Horticultural Substrate; Peat
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.4 No.5,
May
29,
2013
ABSTRACT: An important parameter for
describing oxygen availability in growing media is the air capacity, but this
parameter does not include any information about the gas exchange with the
surrounding atmosphere. The oxygen diffusion coefficient fulfills this
requirement and may be better suited as a characteristic parameter to describe
the oxygen regime. The measurement of the gas diffusion coefficient is a common
method to describe the oxygenation in mineral soils, but this method has not
been studied well on growing media yet. In this investigation four different
growing media were used to measure the oxygen diffusion coefficient at two
different bulk densities and four different water tensions in the laboratory. The effect of density and
water tension on the oxygen diffusion coefficient in different growing media
and the dependence on air content were investigated. The results show that both water tension and density have a major
influence on oxygen
diffusion. With increasing density and moisture content, a decrease of the
oxygen diffusion coefficient can be observed. Between the substrates there are
no significant differences regarding the oxygen diffusion coefficient at the
same air content. Based on the oxygen diffusion coefficients of the substrates,
the models describing the dependence
of gas diffusion coefficients to air content in the literature were tested for
the transferability to growing media. The Moldrup model [1] shows the best fit.
The fit can be slightly further improved by modifying the tortuosity parameter.