THE HYDRAULIC PROPERTIES OF GROWING MEDIA - FROM LABORATORY MEASUREMENTS TO GREENHOUSE MANAGEMENT

R. Wallach, M. Raviv
The knowledge of hydraulic properties of growing media is essential for appropriate management of water-air relationship, nutrients and oxygen transport and their availability to plant roots. In general, the only hydraulic property that is directly measured is the theta - h relationship of the growing medium. The other hydraulic relationships are indirectly estimated from the measured theta - h relationship. The theta - h relationship for a given growing medium is measured in the laboratory by measuring the water content of the sample, theta, at a given tension head, h, when equilibrium has reached (time scale of days, weeks). A question arises whether such theta - h relationships adequately describe the transient theta - h relationships in the growing medium during wetting, drainage or water extraction by roots when significant changes take place during short time periods (minutes, hours). Are the in situ theta - h relationships depend on irrigation frequency, plant-roots spatial distribution, momentary atmospheric demand, etc. This study looks into some of these questions by comparing laboratory-measured and in situ-measured theta - h relationship. The later were obtained by frequent and independent measurement of theta and h variation with time at two heights in the growing container. Horizontally-installed electro-tensiometers and vertically-installed TDR probes were used to measure h and theta, respectively in a growing container filled with tuff (volcanic ash, scoria) in which roses were grown. Overall, the in situ theta - h relationships differed from the laboratory-measured theta - h relationships. Higher moisture contents were measured in situ for given tension heads compared to those measured in the laboratory. It was found that the deviations between the in situ- and the laboratory-measured theta - h relationships depend on the irrigation frequency and spatial roots distribution. The sources of these deviations and their implication to water availability to the plant roots and irrigation management were analyzed and discussed.
Wallach, R. and Raviv, M. (2008). THE HYDRAULIC PROPERTIES OF GROWING MEDIA - FROM LABORATORY MEASUREMENTS TO GREENHOUSE MANAGEMENT. Acta Hortic. 779, 263-272
DOI: 10.17660/ActaHortic.2008.779.32
https://doi.org/10.17660/ActaHortic.2008.779.32
θ - h relationship, in situ measurement, laboratory measurement, tensiometer, TDR, water availability, dynamic retention curve, Rosa hybrida
English

Acta Horticulturae