ANGERS, FRANCE--The physical properties of various growing media used in horticulture are usually characterized by their water retention capabilities during the drying process. Because of the limited volume of growing containers, water content in growing media changes more frequently and more significantly than the water content in soil. Consequently, the physical properties of growing media that have undergone many drying/rewetting cycles change more radically, resulting in considerable variations in water and air availability for container-grown plants. Scientists in France have determined that a new laboratory device can accurately measure water retention and irrigation properties of Sphagnum peat, a popular plant growing material.
"In horticulture, the ability to precisely measure the water retention and shrink/swell properties of growing media or soil over time is an important aspect of irrigation and fertilization management," said Jean-Charles Michel, lead author of a report published in HortScience. Michel and colleagues Guifang Qi, Pascal Boivin, and Sylvain Charpentier adopted a method originally developed by Boivin for simultaneous and continuous measurements of water retention and shrinkage/swelling curves, and adapted the method to the measurement of drying/wetting cycles with different drying intensities.
"The results from this method were encouraging," said Michel. "The experiments (on slightly decomposed Sphagnum peat) showed that, regardless of the intensity of drying, water retention and shrink/swell properties are mainly modified after the first drying process, resulting in losses of water retention and volume after the first cycle, whereas the general physical behavior for the other cycles does not significantly change with reversible hysteresis phenomena."
The research team noted that the method had several limitations, most notably the limited range of water potentials in the case of soil study as compared with growing media for which water is generally managed in this range, and the relatively poor accuracy of pressure head data obtained close to saturation. "Nevertheless, this set-up could make it possible to evaluate the possible evolutions or physical stability of growing media or soil according to water regime history in the laboratory to manage irrigation accordingly," the report concluded.
The complete study and abstract are available on the ASHS HortScience electronic journal web site: http://hortsci.ashspublications.org/content/46/9/1298.abstract
Founded in 1903, the American Society for Horticultural Science (ASHS) is the largest organization dedicated to advancing all facets of horticultural research, education, and application. More information at ashs.org
A Laboratory Device for Continual Measurement of Water Retention and Shrink/Swell Properties during Drying/Wetting Cycles
Guifang Qi, Jean-Charles Michel, Pascal Boivin, and Sylvain Charpentier
HortScience 46:1298–1302. [Abstract][Full Text][PDF]