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Donald R. Davis

) reviewed the evidence for this well-known “dilution effect.” Although their review has been cited over 180 times (60 times from 2000 on), few mentions of the dilution effect contain a reference, suggesting that the effect is widely regarded as common

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Desmond G. Mortley, Stephanie Burrell, Conrad K. Bonsi, Walter A. Hill, and Carlton E. Morris

concentration in the leaves of plants exposed to the longer light period and lower irradiance may have been the result of a “dilutioneffect as evidenced by the greater storage root and foliage production among these plants. All leaf elemental concentrations

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Martin P.N. Gent and Michael R. Short

the volume and concentration of nutrient solution supplied. Environment has an effect on transpiration rate and water uptake through radiation and air temperature ( Norrie et al., 1994 ). Nitrogen use may change with radiation integral ( Charbonneau et

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Juan Carlos Díaz-Pérez and Touria E. Eaton

.0 at 167% ETc. In 2011, CI decreased from 55.8 at 33% ETc to 53.7 at 167% ETc ( Table 1 ). Decreased CI values with increased irrigation rates were likely due to dilution effect of nutrients, since plant growth was enhanced with increased irrigation

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Juana C. García-Santiago, Luis A. Valdez-Aguilar, Armando Hernández-Pérez, Andrew D. Cartmill, and Jesús Valenzuela-García

dilution effect associated with the higher biomass produced by these plants, as suggested by the higher total content of Ca in subirrigated plants when compared with drip-fertigated plants. Phosphorus concentration was affected in the root and in the whole

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David R. Hershey and Susan Sand

A Venturi-type proportioner (VP), trade name Hozon, can be used for an inexpensive, hands-on laboratory exercise that demonstrates the effect of water pressure on dilution ratio and water flow. Using electrical conductivity (EC) meters to determine solution concentration allows students to discover that the dilution ratio increases with water pressure, from 1:10 at 15 psi to 1:15 at 55 psi. The greater dilution at higher pressure can be explained by measuring the water flow, which is 2.3 gal/min (8.7 litersžmin-1) at 15 psi but 3.5 gal/min (13.2 litersžmin-1) at 55 psi. Experiments relating water pressure to dilution ratio provide experience in use and calibration of VPs and EC meters, as well as graph preparation and interpretation.

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Harvey J. Lang

Analysts of potting media for pH and electrical conductivity (EC) can be a useful tool for monitoring the nutritional status of greenhouse grown plants. This research examined the variability associated with procedures involved in the determination of pH and EC in greenhouse potting media. Three commonly used methods, the 1:5 dilution, the 1:2 dilution and the saturated media extract, were examined on several different commercial potting media. Because of the different dilution volumes used, there were significant differences in pH and EC between the three methods for all media tested. Within each method, results varied baaed on whether readings were taken in the slurry, solution phase, or extract, with extracts resulting in consistently higher pH, but lower EC values. There was a significant effect of medium-solution equilibration time on both pH and EC, with variability decreasing after 30 minutes of equilibration. Samples taken from the upper half of pots had higher EC readings than those collected from the bottom half of pots only on plants fertilized with N concentrations greater than 200 ppm. There was also slight variability between the different calibrated instruments used in determining pH and EC. Details of each study along with grower recommendations will be discussed.

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J. Roger Harris, Patricia Knight, and Jody Fanelli

Two rootball sizes as well as a nontransplanted control were randomly assigned to Acer saccharum Marsh. (sugar maple) trees in four adjacent nursery rows at Waynesboro Nurseries in Waynesboro, Va. One size (75 cm in diameter) corresponded to the American Association of Nurserymen standards. The other rootball size was 90 cm in diameter. Trees were transplanted just before bud swell or during shoot elongation. Rootball size had no effect on height, stem diameter, or twig growth, total nonstructual leaf nitrogen content (LNC), or total stem nonstructual carbohydrate (TNC). Height growth was reduced by 81%, stem diameter growth by 71%, and twig growth by 82% for trees transplanted before bud swell compared to nontransplanted trees. LNC was 25% more on transplanted trees than on nontransplanted trees, presumably due to a dilution effect. TNC was 20% higher on transplanted compared to nontransplanted trees. Growth was severely curtailed on late-transplanted trees for all characteristics measured compared to all other treatments.

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U. Afek, L.A. Lippet, D. Adams, J.A. Menge, and E. Pond

Vesicular–arbuscular mycorrhizal inoculum consisting of a mixture of roots of coast redwood [Sequoia sempervirens (D. Don)], soil, and spores of Glomus mosseae (Nicol. and Gerd.) Gerdemann and Trappe was tested for viability and efficacy following storage for 4 or 8 weeks at 4, 9, 15, or 24C and moisture contents of 0%, 6%, 12%, or 17%. Storage regimes did not have any effect on the number of spores of Glomus mosseae recovered after storage. However, germinability of the spores decreased from 35% before storage to 10% to 31% during storage, especially under typical ambient room conditions (17% moisture at 24C). Maximum colonization of coast redwood, sierra redwood [Sequoiadendrom giganteum (Lindl.) Buchh.], and incense cedar (Libocedrous decurrens Torr.) was achieved after inoculation with 1 inoculum: 1 potting mix dilution (w/w). However, plant fresh weight was highest following inoculation with a 1 inoculum: 5 potting mix dilution (w/w). Dried inoculum was effective when stored at 24C, or below 10C when moist.

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Steven A. Weinbaum, Wesley P. Asai, David A. Goldhamer, Franz J.A. Niederholzer, and Tom T. Muraoka

There is legitimate concern that excessive fertilizer nitrogen (N) application rates adversely affect groundwater quality in the San Joaquin Valley of California. A 5-year study was conducted to assess the interrelationships between N fertilization rates, tree productivity, leaf [N], soil [NO 3], tree recovery of isotopically labeled fertilizer N, and NO 3 leaching. High N trees recovered <50% as much labeled fertilizer N in the crop as did trees previously receiving low to moderate fertilizer application rates. Our data suggest that the dilution of labeled N in the soil by high residual levels of NO 3 in the soil had a greater effect than tree N status (as expressed by leaf N concentration) on the relative recovery of fertilizer N.