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Title: Developing Moisture Characteristic Curves and Their Descriptive Functions at Low Tensions for Soilless Substrates

item Altland, James
item OWEN JR., JAMES - Oregon State University
item FONTENO, WILLIAM - North Carolina State University

Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/9/2010
Publication Date: 11/23/2010
Citation: Altland, J.E., Owen Jr., J.S., Fonteno, W. 2010. Developing moisture characteristic curves and their descriptive functions at low tensions for soilless substrates. Journal of the American Society for Horticultural Science. 136(6):563-567.

Interpretive Summary: Moisture characteristic curves (MCC) are useful for describing the water holding characteristics of a soil or soilless substrate. They relate the amount of water held to the pressure exerted on a substrate. MCC are difficult to develop for soilless substrates at low tensions with currently used methods. Furthermore, methods for developing MCC are time-consuming and laborious. We developed a new Modified Long Column (MLC) technique for rapidly generating MCC at low tension, making them ideal for use on soilless substrates. Our data show that the MLC is rapid and more precise at low tensions compared to traditional methods. However, the MLC method is limited to low tension ranges, and thus not useful when tensions greater than 150 cm are required. The MLC method will expedite development of MCC for common nursery substrates, and allow nursery professionals and university extension faculty to more precisely understand the differences in water holding characteristics of soilless substrates.

Technical Abstract: Moisture characteristic curves (MCC) relate the water content (') in a substrate to the matric potential ('m) at a given tension or height (h). Most techniques for developing MCC are not well-suited coarse substrates such as those composed of bark used in container nursery substrates. The objectives of this research were to compare an inexpensive modified Long Column (MLC) method to an established method for creating low tension MCCs, and then to determine the best model for describing MCCs of bark based soilless substrates. Three substrates composed of Douglas fir bark alone or mixed with either peat moss or pumice were used to compare models. Both methods described differences between the three substrates, although MCC for each method differed within a substrate type. A four parameter log-logistic function was determined to be the simplest and most explanatory model for describing MCC of bark based substrates.