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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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Daniel C. Bowman, Richard Y. Evans and J.L. Paul

Hydration of three commercial hydrophilic polyacrylamide gels in deionized water ranged from 340 to 420 g per gram of gel. Hydration was progressively inhibited by fertilizer salt concentrations from 0 to 20 meq·liter-1. Hydration of the gels in the presence of divalent cations (Ca2+ and Mg2+) and monovalent cations (K+ and NH4 +) at 20 meq·liter-1 was reduced to ≈10% and 20% of maximum, respectively. The valence of the accompanying anion did not affect hydration. Gel hydration was unaffected by urea over the range of 2 to 20 mm. Sequential rinses of the hydrated gels with deionized water completely reversed the inhibition due to the monovalent, but not the divalent, cations. The electroconductivity (EC) of the external solution increased during gel hydration. In the presence of fertilizer salts, the physical properties of a 2 redwood sawdust : 1 sand (v/v) container mix were unaffected by hydrophilic gel additions of 1.2 and 2.4 kg·m-3 (1 × and 2 × the recommended rate, respectively).

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Celso L. Moretti, Steven A. Sargent, Donald J. Huber, Adonai G. Calbo and Rolf Puschmann

`Solar Set' tomatoes (Lycopersicon esculentum Mill.) were harvested at the mature-green stage of development and treated with 50 μL·L-1 ethylene at 20 °C. Breaker-stage fruit were dropped from 40 cm onto a solid surface to induce internal bruising and held along with undropped fruit at 20 °C. At the ripe stage, pericarp, locule, and placental tissues were analyzed for soluble sugars, vitamin C, pigments, titratable acidity, soluble solids content, pericarp electrolyte leakage, extractable polygalacturonase activity, and locule tissue consistency. Bruising significantly affected chemical composition and physical properties of pericarp and locule tissues, but not placental tissue. For bruised locule tissue, carotenoids, vitamin C, and titratable acidity were 37%, 15%, and 15%, lower, respectively, than unbruised fruit. For bruised pericarp tissue, vitamin C content was 16% lower than for unbruised tissue, whereas bruising increased electrolyte leakage and extractable polygalacturonase activity by 25% and 33%, respectively. Evidence of abnormal ripening following impact bruising was confined to locule and pericarp tissues and may be related to the disruption of cell structure and altered enzyme activity.

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Charlotte Mundy, Nancy G. Creamer, L. George Wilson, Carl R. Crozier and Ronald D. Morse

Conservation tillage using residue from a cover crop grown before potato (Solanum tuberosum L.) production has been infrequently and inconclusively studied. The objectives of this study were to 1) conduct a field study to evaluate soil physical properties, and potato growth and yield, in conventional-tillage (CT), no-tillage (NT), and subsurface-tillage (SST) systems and 2) conduct a greenhouse study to evaluate the effect of soil bulk density (ρb) on potato growth and yield. Potatoes (`Atlantic') were planted into residue of sorghum-sudangrass [Sorghum bicolor (L.) Moench × S. sudanense (Piper) Staph] at two sites in eastern North Carolina—Plymouth into Portsmouth fine sandy loam and Lewiston into Norfolk sandy loam. Potatoes in the NT and SST system emerged more slowly than potatoesplanted conventionally. There were no differences in plant population or size by 8 weeks after planting at Plymouth, but plant population and size were less in NT and SST systems at Lewiston. Reducing tillage also affected soil compaction, increased soil moisture early in the season at both sites, and increased ρb at Lewiston. Yield of U.S. No. 1 potatoes planted in NT and SST systems were comparable to potatoes planted in a CT system at Plymouth, but were less than potatoes planted in a CT system at Lewiston. There were no differences in yield between potatoes planted with NT and SST. In the greenhouse study, ρb did not affect leaf area or tuber yield or tuber grade. Specific sites and soils may allow for comparable potato production with no or SST, but further research, conducted on different soil types would promote further understanding of the impacts of reducing tillage in potato production.

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James S. Owen Jr and James E. Altland

substrate physical properties as it has on soil physical properties. Texture for soilless substrates can be defined as the distribution and proportions of particle sizes in a substrate resulting from grinding, processing, and decomposition of the parent

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Michael R. Evans and Mary M. Gachukia

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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Patrice Cannavo, Houda Hafdhi and Jean-Charles Michel

an extensive list of abiotic factors that influence root growth in containers in their review. Among them, the physical properties of growing substrate are of great importance. The air-filled porosity and the water retention capacity and availability

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Glenn B. Fain and Charles H. Gilliam

The objective of this study was to evaluate the potential use of container substrates composed of whole pine trees. Three species [loblolly pine (Pinus taeda), slash pine (Pinus elliottii) and longleaf pine (Pinus palustris)] of 8–10 year old pine trees were harvested at ground level and the entire tree was chipped with a tree chipper. The chips from each tree species were then further processed with a hammer mill to pass a ½-inch screen. On 29 June 2005 these three substrates along with 100% pinebark were mixed with the addition per cubic yard of 9.49 kg·m–3 Polyon 18–6–12 (18N–2.6P–10K), 2.97 kg·m–3 dolomitic lime and 0.89 kg·m–3 Micromax. One gallon (3.8 L) containers were then filled and placed into full sun under overhead irrigation. Into these containers were planted 72 cell plugs of Catharanthus roseus`Little Blanche'. Data collected were pre-plant chemical and physical properties of substrates, as well as plant growth index (GI), plant top dry weight, root ratings, and plant tissue (leaves) nutrient analysis at 60 days after planting (DAP). The test was repeated on 27 Aug. 2005 with C. roseus Raspberry Red Cooler. Top dry weights were on average 15% greater for the 100% pinebark substrate over all others at 60 DAP. However there were non differences in plant GI for any substrate at 60 DAP. There were no differences in plant tissue macro nutrient content for any substrate. Tissue micronutrient content was similar and within ranges reported by Mills and Jones (1996, Plant Analysis Handbook II) with the exception of Manganese. Manganese was highest for slash and loblolly pine and well over reported ranges. There were no differences in root ratings. There were no differences in substrate physical properties between the three whole tree substrates. However the 100% pinebark substrate had on average 50% less air space and 25% greater water holding capacity than the other substrates. Physical properties of all substrates were within recommended ranges. Based on the results of this study substrates composed of whole pine trees have potential as an alternative sustainable source for a substrate used in producing short term nursery crops.

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Philippe Jobin, Jean Caron, Pierre-Yves Bernier and Blanche Dansereau

Hydrophilic polymers or hydrogels have shown potential to increase water retention of media and to reduce irrigation frequency. This property would be particularly useful in the production of fast growing species in which large amounts of water are needed. This study evaluated the effect of two acrylic-based hydrogels on water desorption curve and hydraulic conductivity of substrates and on plant growth. The duration of their effects was also investigated. Rooted cuttings of Surfinia (Petunia ×hybrida `Brilliant Pink') were transplanted into 30-cm pots containing one of three different substrates amended with one of two types of hydrogels, a commercial acrylic polymer, and a commercial acrylic-acrylamide copolymer, and grown for 9 weeks under well watered conditions and then imposed with a drought. Results indicated that both polymer types gave similar results. The substrates' physical properties (air-filled porosity, available water) at potting time were significantly affected by hydrogel addition, but differences vanished within 9 weeks of growth. Hydrogels had no significant effect on the point at which plant wilted and on the substrate's unsaturated hydraulic conductivity. Shoot dry weight was affected by substrate and hydrogel and was positively correlated to water content between container capacity and -10 kPa of water potential, or between container capacity and the soil water potential at plant turgor loss.

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William C. Fonteno and Paul V. Nelson

Loose rockwool had a total porosity similar to peatmoss (92%, by volume) but with water retention capabilities similar to sand. Root media formulations containing loose rockwool were tested with seven plant species for plant response and nutrient uptake. The volume percent formulation, 20 rockwool : 10 peatmoss : 20 vermiculite : 45 pine bark : 5 perlite, was superior to formulations containing 10% or 30% rockwool. Plant response in this rockwool medium in bedding plant flats was superior to that in two high-performing commercial media for impatiens (Impatiens sultanii Hook), marigold (Tagetes patula L.), and petunia (Petunia hybrida Vilm) and equal to one commercial medium for tomato (Lycopersicon esculentum Mill.). However, response of chrysanthemum (Chrysanthemum × morifolium Ramat.), geranium (Pelargonium × hortorum Bailey), and poinsettia (Euphorbia pulcherrima Willd. ex Kl.) in 1.58-liter pots was inferior to both commercial media in one-half of the trials. Differential plant responses in the root media treatments did not relate directly to differences found to occur in plant nutrient composition. The high initial pH level of rockwool necessitated reduced application of limestone and increased application of calcium sulfate to offset Ca deficiency.