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George Gizas and Dimitrios Savvas

performance in each treatment, the particle size distribution and the moisture retention curve for each grade of pumice were also determined. Materials and Methods Physical characteristics of the substrate The particle size distribution of the four

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E. Jay Holcomb, Robert Berghage and William Fonteno

The concepts of container water-holding capacity and air-filled porosity are important yet complicated for students interested in containerized crop production; however, both of these concepts can be observed and understood more completely if students develop a moisture retention curve. Our objectives were to describe an easy-to-construct and economical apparatus for creating a moisture retention curve and then to compare this curve with one generated by standard methods. The student method (column method) is constructed from plastic pipe cut into 5-cm sections. The sections of pipe are individually packed with a substrate then stacked and taped together, resulting in a 60-cm column of the substrate. The column is saturated and allowed to drain for 24 h. Then, the column is taken apart and the water content of each section determined gravimetrically. The water content of each section is graphed against height so that the result is a moisture retention curve. Data are presented to show the curve developed from the column method is similar to the curve developed by standard soil moisture tension method. The moisture retention curve can provide a better understanding of water and air holding capacities of substrates.

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Michael Raviv, J. Heinrich Lieth, David W. Burger and Rony Wallach

We are grateful to the Joseph Hill Foundation and Roses Incorporated for providing financial support for this research. We also acknowledge assistance of Shlomit Medina who conducted measurements for the moisture retention curves. The cost of

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William C. Fonteno, Matthew S. Drzal and D. Keith Cassel

The influence of substrate physical properties on water transport and plant growth must be known if irrigation water use efficiency is to be improved. Three fundamentally different substrates were examined: 1 peat moss: 1 vermiculite (v/v), 3 pine bark: 1 peat: 1 sand, and 1 mineral soil: 1 peat: 1 sand. Capacity analyses included total porosity, container capacity, air space, available water and unavailable water. Water transport was characterized by saturated and unsaturated flow analyses. A new method, Pore Fraction Analysis, was developed to characterize substrate pore structure into fractions based on function with the substrate. This method is based on soil moisture retention curves, pore size distributions, and average effective suction at container capacity (AEScc) This method is offered to expand the traditional terms of macropore and micropore into new definitions: macropores, mesopores, micropore, and ultramicropore; each based on a range of pore sizes and functions. Computer simulation models of air and water profiles were run on several container sizes with the three test substrates. Pore fraction analysis indicated that under traditional production practices macropores indicate the volume of a substrate that be filled with air at container capacity, the mesopore fraction effectively fills and drains with daily irrigation, the micropore fraction functions as a measure of water reserve, while the ultramicropores contain water unavailable to the plant.

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Jeb S. Fields, William C. Fonteno, Brian E. Jackson, Joshua L. Heitman and James S. Owen Jr.

Identifying a substrate’s ability to hold and release water is critical to improving the efficiency of water use in greenhouse crops. Moisture retention curves (MRCs) in soilless substrates were first described by Bunt (1961) and are obtained in a

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Yong Ha Rhie and Jongyun Kim

porosity = container capacity + air space. Bulk density was calculated by dividing dry weight (24 h at 105 °C) by volume. Moisture retention curves of each substrate mix were determined using a sandbox apparatus (Eijkelkamp, Giesbeek, the Netherlands) at

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Yong Ha Rhie, Seonghwan Kang and Jongyun Kim

and the substrate matric potential dropped to −1.1 kPa ( Fig. 1 ), which agrees with that reported by Wang (2010) . Fig. 1. Moisture retention curve of sphagnum moss. Automated irrigation system. The θ measurements in the moss decreased gradually

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George Kotsiris, Panayiotis A. Nektarios and Angeliki T. Paraskevopoulou

organic matter by combustion, the mechanical analysis of the substrates was performed using the dry-sieving method according to ASTM D422-63 (2007) with the use of a vibrating sieve shaker (AS 200; Retsch GmbH, Haan, Germany). Moisture retention curves

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Denise Neilsen, Gerry Neilsen, Sunghee Guak and Tom Forge

(<2%), low native fertility, drain rapidly, and generally have low water-holding capacity. Soil moisture retention curves determined on four undisturbed surface samples collected from the experimental block before planting indicated average volumetric

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Marc W. van Iersel, Matthew Chappell and John D. Lea-Cox

small pores. The relationship between VWC and matric potential can be determined from moisture release curves ( Fig. 4 ). Fig. 4. A substrate moisture retention curve (pF vs. volumetric water content) and the hydraulic conductivity as a function of pF