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properties as required by the specific crop and growing conditions ( Bunt, 1988 ). An important physical property of substrates is air-filled pore space. Air-filled pores allow for drainage and gas exchange between the root environment and the outside

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either 20% perlite or 20% composted bark and a total of 0%, 10%, 20%, or 30% feather fiber in the final root substrate ( Table 1 ) with the remainder being sphagnum peat. A total of eight substrates were formulated. Table 1. Total pore space, air-filled

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would be useful. However, the impact of the decrease in air-filled porosity is not known because it could lead to decreased aeration but may also have no impact if pore connectivity improvement leads to better air exchange. This point deserves further

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containers used for testing were 3.785-L Poly-Tainer PTC700 (Nursery Supplies). Container volume was measured and it was then filled with oven-dried substrate and weighed to determine dry weight. Water was added until all pore spaces were filled. Water was

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substrate physical properties include TPS, AFP, WHC, and bulk density. Air-filled pore space is particularly important because air-filled pores allow for gas exchange between the root environment and the outside atmosphere ( Bunt, 1988 ). Various materials

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air-filled pore space of 69% (v/v). Evans and Gachukia (2007) demonstrated that the large particle size of whole parboiled fresh rice hulls increased drainage and air-filled pore space in peat-based substrates without causing significant nitrogen

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granulates (1-mm diameter) were obtained from Amorim Cork Composites (Chicago, IL). Vermiculite and cork were packed into 345-mL porometers (7.5 × 7.5 cm), and bulk density (grams per cubic centimeter), total pore space (percent v/v), air-filled pore space

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conditions. The components used to formulate the substrate and the proportions of the components may be altered to change the physical properties of the substrate as desired ( Bunt, 1988 ). Total pore space, air-filled pore space, waterholding capacity

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estimated substrate matric potential measurements for the dry treatments are projected tensions. Air-filled pore space was determined by subtracting VWC from total pore space. Air-filled pore space in Fafard was maintained between 12% and 20% in the wet

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Two grades of ground bovine bone were evaluated as potential alternatives to perlite in horticultural substrates. The bulk density of small and large bone-amended substrates was significantly higher than equivalent perlite-amended substrates. Large and small bone increased the air-filled pore space of sphagnum peat. However, at 10% and 20% (v/v), neither size of bone resulted in as high an air-filled pore space as equivalent amounts of perlite. At 30% and 40%, incorporation of small bone resulted in a similar air-filled pore space as incorporation of equivalent amounts of perlite, and incorporation of large bone resulted in a higher air-filled pore space than incorporation of equivalent amounts of perlite. Water-filled pore space and water-holding capacities of substrates were inversely related to air-filled pore space. When placed in a moist substrate, mineral elements within the bone were able to leach into the substrate over time. Substrates amended with 40% large and small bone had significantly higher concentrations of ammonium (NH4 +), phosphorus (P), potassium (K), calcium (Ca), sodium (Na), and chloride (Cl-) than the 40% perlite-containing substrates. Substrates amended with 40% large bone had similar concentrations of magnesium (Mg), sulfur (S), iron (Fe), and copper (Cu) while substrates amended with 40% small bone had higher levels of these elements than perlite-amended substrates. Substrate concentrations of nitrate (NO3 -), manganese (Mn), zinc (Zn), and boron (B) were not different among the substrates after 4 weeks in the greenhouse. The pH, electrical conductivity (EC) and NH4 + levels of bone-amended substrates increased to levels significantly higher than recommended and resulted in rapid mortality of `Orbit Cardinal' geranium (Pelargonium × hortorum), `Cooler Blush' vinca (Catharanthus roseus), and `Dazzler Rose Star' impatiens (Impatiens walleriana) plants grown in bone-amended substrates. Therefore, ground bovine bone was not a feasible alternative to perlite for use in horticultural substrates.

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