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Andrew G. Reynolds and Andrew P. Naylor

Glasshouse-grown `Pinot noir' and `Riesling' grapevines (Vitis vinifera L.) were subjected to one of four water stress durations [no water deficit (control); and water deficits imposed postbloom, lag phase, and veraison] in combination with three soil water-holding capacities (0%, 26%, and 52% gravel, by volume). Vines subjected to increasing water stress duration had less cumulative lateral shoot length and lower shoot count, leaf size, and berry weights than those not stressed. Soluble solids concentration (SSC) during maturation and pH at harvest also increased with increasing water stress duration, but titratable acidity was not affected. Transpiration and stomatal conductance also were reduced with increased water stress duration, but soil water increased, reflecting the larger leaf surface on vines with veraison-imposed deficits. Reducing water-holding capacity (by increasing the percentage of gravel in the soil) tended to increase berry weight and SSC but reduced lateral shoot growth. The 52% gravel treatments increased transpiration rate and stomatal conductance for `Riesling' but reduced them slightly in `Pinot noir'. Percentage of soil moisture was reduced linearly with reduced water-holding capacity. These results indicate that early irrigation deficits may advance fruit maturity of wine grapes with concomitant reductions in vegetative growth. Differential responses of these cultivars to soil water-holding capacity also should help to identify suitable wine grape cultivars as the wine grape industry expands into areas with low water-holding capacity soils.

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William R. Argo and John A. Biernbaum

Hybrid impatiens were grown in 15 cm pots containing one of six root medium. After seven weeks, plant available water holding capacity (AWHC) was measured as the difference between the drained weight of the plant and pot after a one hour saturation and the weight of the pot when the plant wilted. Water absorption potential (WAP) was calculated as the capacity of each root medium to absorb applied irrigation water up to the AWHC and was measured at two moisture levels with top watering (two leaching fractions), drip irrigation (two leaching fractions) and flood subirrigation. Top watering moist media (initial AWHC = 35%) with leaching fractions of 30+ % was me most efficient method of rewetting media and was the only irrigation method tested to obtain WAP's of 100%. In comparison, flood subirrigation was the least efficient method of rewetting media with WAP of 27% for dry media (initial AWHC = 0%), and obtained a total WAP of 55% for moist media (initial AWHC = 23%). In media comparisons, the incorporation of a wetting agent into a 70% peat/30% bark mix at planting increased the WAP compared to the same media without a wetting agent with nine of the ten irrigation treatments.

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Michael R. Evans, Giampaolo Zanin and Todd J. Cavins

properties of substrates are bulk density, total pore space, air-filled pore space, and water-holding capacity. Bulk density refers to the weight of a given volume of substrate and is most commonly reported as grams of dry weight per 100 cm 3 of substrate

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Michael R. Evans and Mary M. Gachukia

compare total pore space (% by volume), air-filled pore space (% by volume), water-holding capacity (% by volume and weight per weight), and bulk density (weight per volume) of sphagnum peat-based substrates amended with various amounts of PBH or perlite

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James S. Owen Jr and James E. Altland

materials and added components. Mechanical analysis ( Dane and Topp, 2002 ) of substrate particle size distribution is routinely performed to make inferences on infiltration, pore size and distribution, and, subsequently, water-holding capacity ( Argo, 1998

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Johann S. Buck and Michael R. Evans

million tons of fresh rice hulls were produced annually in the United States. According to Bunt (1988) and Hanan (1998) , fresh rice hulls had a bulk density of 0.10 g·cm −3 , water-holding capacity of 20% (v/v), total pore space of 89% (v/v), and an

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Arianna Bozzolo and Michael R. Evans

, vermiculite has been blended with peat as a component to increase substrate water-holding capacity ( Boodley and Sheldrake, 1977 ; Stamps and Evans, 1999 ). Additionally, vermiculite has been commonly used as a top coating material because it is sterile

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John M. Ruter and Hendrik van de Werken

The effect of container design on physical parameters of media with different bulk densities was evaluated. A significant interaction between container design and media for water-holding capacity and air space was found. A container with a polyester fabric bottom had the largest media air space and the smallest water-holding capacity after 24 h of drainage when placed on a column of sand to allow for free drainage from the container medium. For the media tested, a blend of composted pine bark and hardwood bark (PB:HB) appeared to have good physical characteristics for a container medium in the container designs that were evaluated. Container design should be considered when selecting a container medium because physical parameters of a given medium will be influenced.

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Michael R. Evans

Aggregates produced from finely ground waste glass [Growstones (GS); Earthstone Corp., Santa Fe, NM] have been proposed to adjust the physical properties of peat-based substrates. The GS had a total pore space (TPS) of 87.4% (by volume), which was higher than that of sphagnum peat and perlite but was similar to that of parboiled fresh rice hulls (PBH). The GS had an air-filled pore space (AFP) of 53.1%, which was higher than that of sphagnum peat and perlite but lower than that of PBH. At 34.3%, GS had a lower water-holding capacity (WHC) than sphagnum peat but a higher WHC than either perlite or PBH. The bulk density of GS was 0.19 g·cm−3 and was not different from that of the perlite but was higher than that of sphagnum peat and PBH. The addition of at least 15% GS to sphagnum peat increased the AFP of the resulting peat-based substrate. Substrates containing 25% or 30% GS had a higher AFP than substrates containing equivalent amounts of perlite but a lower AFP than substrates containing equivalent PBH. Substrates containing 20% or more GS had a higher WHC than equivalent perlite- or PBH-containing substrates. Growth of ‘Cooler Grape’ vinca (Catharanthus roseus), ‘Dazzler Lilac Splash’ impatiens (Impatiens walleriana), and ‘Score Red’ geranium (Pelargonium ×hortorum) was similar for plants grown in GS-containing substrates and those grown in equivalent perlite- and PBH-containing substrates.

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Robert H. Stamps and Michael R. Evans

A comparison was made of Canadian sphagnum peat (SP) and Philippine coconut (Cocos nucifera L.) coir dust (CD) as growing media components for Dieffenbachia maculata [(Lodd.) G. Don] `Camille' greenhouse production. Three soilless foliage plant growing mixes [Cornell, Hybrid, Univ. of Florida #2 (UF-2)] were prepared using either SP or CD and pine bark (PB), vermiculite (V), and/or perlite (P) in the following ratios (percent by volume): Cornell = 50 CD or SP:25 V:25 P, Hybrid = 40 CD or SP:30 V:30 PB, UF-2 = 50 CD or SP:50 PB. Initial CI concentrations and electrical conductivities were higher for CD-containing media (CDM) than SP-containing media (SPM). At termination, Ca, Mg, and NO3-N concentrations were higher for SPM than CDM. Bulk densities were lower for CDM than SPM for one medium, but not for the others. Water-filled pore space (W-FPS) and water-holding capacity (W-HC) were larger and air-filled pore space (A-FPS) generally was smaller for CDM than SPM. Cornell had the highest W-FPS and W-HC, lowest A-FPS and percentage of large particles, and produced the highest grade and heaviest plants. Plant top grades, fresh mass and overall mass, but not root grades and mass, were higher for CDM than SPM. Plant mass was positively correlated with initial medium W-HC but not with A-FPS. Lower K in mix UF-2 compared to the mixes containing vermiculite may have been partly responsible for the lesser growth in that mix.