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James E. Altland and Ka Yeon Jeong

extraction of the water from the substrate and through the filter paper. Filtrates were immediately placed in a refrigerator and stored at 2 °C until the time of analysis. At analysis, pH was determined with a pH/ion analyzer (MA 235; Metler Toledo, Columbus

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Annick Moing, Laurence Svanella, Dominique Rolin, Monique Gaudillère, Jean-Pierre Gaudillère and René Monet

Changes in metabolites were studied during the fruit development of two greenhouse grown peach [Prunus persica (L.) Batsch] cultivars with low acidity (`Jalousia') or normal acidity (`Fantasia'). Both cultivars had the same sucrose concentration in fruit mesocarp at maturity. In the fruit juice, pH was higher and titratable acidity was lower for `Jalousia' than for `Fantasia' from 80 days after bloom to maturity. At four different times during fruit development, in vivo 13C NMR spectroscopy was used to measure the vacuolar pH of fruit mesocarp. At 55 days after bloom, the vacuolar pH of fruit mesocarp was not significantly different between `Jalousia' and `Fantasia', whereas the juice pH was different between cultivars. The three major organic acids in fruit mesocarp were malic, citric, and quinic acids for both cultivars. Citric acid concentrations were similar in both cultivars until ≈85 days after bloom and then became significantly higher in `Fantasia'. A significantly higher concentration in malic acid in `Fantasia' than in `Jalousia' was observed from the end of the first growth phase to maturity. At maturity, `Fantasia' fruit had two and five times more malic and citric acid, respectively, than `Jalousia' fruit. The differences observed between `Jalousia' and `Fantasia' fruit for malic and citric acid concentrations accounted for the difference in titratable acidity. The differences in acid concentration appeared during the plateau between the two rapid growth phases of the fruit, i.e., far before the onset of maturation. The three major amino acids were asparagine, glutamic acid, and proline for both cultivars. Their concentration followed similar patterns in acid and low-acid fruit.

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Harvey J. Lang and George C. Elliott

Effects of medium, NH4: N03, ratio, and N fertilizer rate on the development of NH4 oxidation in soilless potting media were evaluated. In two separate experiments, NH4 oxidizing activity increased to a maximum (4 to 6 weeks of cropping) and then dropped off sharply. Ammonium oxidation activity varied significantly among types of soilless potting media. Media fertilized with 1 NH4-N: 3 N03-N had higher rates of NH4 oxidation than media fertilized with ratios of either 1:1 or 3:1. Nitrogen fertilization at 15 mm gave consistently higher oxidation rates than fertilization at 30 mm. In general, media samples that had been cropped with plants had higher nitrifying activity than unplanted samples. Ammonium oxidation rate over all observations was significantly correlated with medium pH (r = 0.50). pH values above 6.8 were necessary but not completely sufficient for relatively high rates of NH4 oxidation. Rates of oxidation were insignificant with pH values <5.6.

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Harvey E. Arjona, Frank B. Matta and James O. Garner Jr.

Fruit growth (diameter) of purple passion fruit (Passiflora edulis Sims.) and maypop (P. incarnata L.) followed a sigmoidal growth curve. Passion fruit were larger than either greenhouse-grown or wild maypop fruit. Wild maypop produced larger fruit than greenhouse-grown maypop. Yellow passion fruit had the lowest percentage of pulp and the highest soluble solids concentration (SSC) and greenhouse-grown maypop had the lowest SSC among the four groups tested. Purple and yellow passion fruit had lower juice pH than maypop. Wild maypop fruit had the highest sucrose content and purple passion fruit had the lowest. Yellow and purple passion fruit juice had higher fructose and glucose contents than did maypop juice.

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Anthony W. Kahtz and Nick J. Gawel

One-year-old `Royal Burgundy' barberry (Berberis thunbergii var. atropurpurea) liners were potted in 1-gal (3.8-L) containers. Container media consisted of noncomposted recycled waste mixed at rates of 0% (control), 25%, 50%, 75%, and 100% by volume with a (by volume) 3 pine bark: 2 peat: 1 sand media. Treatments were replicated eight times. Three grams (0.1 oz) of Osmocote 13-10-13 (13N-4.37P-10.8K) with micronutrients were topdressed on all containers. Media electrical conductivity (EC) and pH readings were recorded every fifteen days over the course of 5 months. Dry shoot, root, and total weights were recorded at the end of the project and a foliar analysis was performed for nutrient and metal content. Results indicate a general trend of higher EC with greater volumes of recycled waste. EC levels for the control and 25% treatment were within recommendations for the optimal plant growth of plants for the duration of the study. All treatments had an acceptable pH level for plant growth. Nitrogen levels were below the recommended foliar analysis sufficiency range. Levels of phosphorus and potassium were above or within the recommended foliar analysis sufficiency range. Metals were below or within recommended ranges for all treatments. Total dry weights revealed no statistical difference between the control, 25%, 50%, and 75% treatments. This study indicates that 25% noncomposted recycled waste could be used in container media for production of `Royal Burgundy' barberry.

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W. Cao and T.W. Tibbitts

Three nutrient culture experiments were conducted to determine the responses of potatoes (Solanum Tuberosum L.) to various solution pH levels with NO3, NH4, and mixed NO3/NH4 (1/1) at the same total N of 4 mM. The pH levels were maintained at 4, 5, 6, and 7 with NO3 or NH4, and at 4, 4.5, 5, 6, 6.5, 7 with mixed N. In each of the experiments, Norland plants were grown for 28 days after transplanting. With mixed N, plant growth as total dry weight, leaf area and tuber number was essentially similar at pH 4.5 to 7, and decreased only at pH 4. However, with either NO3 or NH4 growth peaked at a particular pH level, pH 5 and 6 respectively, and was significantly reduced at other pH levels with severe stunting at pH 7. With mixed N, the concentrations of total N in shoots were similar at pH 4 to 7 whereas, with either N form, the concentrations of total N were higher at particular pH levels, pH 4 and 5 with NO3 and pH 7 with NH4. The concentrations of P, S, Ca, Mg, and Mn in shoots were similar at pH 4 to 7 with mixed N, but varied at certain pH levels with either NO3 or NH4. The results indicate that the useful pH range for nutrient uptake and plant growth is broader with mixed N than with either NO3 or NH4.

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Amy J. Moberg, James J. Luby, Carl J. Rosen and Peter D. Ascher

Accessions of Vaccinium species (deliciosum, ovalifolium, membranaceum, parvifolium, scoparium) were evaluated for tolerance to higher pH in the root zone using an in vitro screening procedure. Seeds were germinated on media containing all essential nutrients with nitrogen in the nitrate form at pH 5 and pH 6 and evaluated for 21 weeks. Excess EDTA was used to buffer the micronutrients and pH was buffered by MES and succinic acid. Germination varied among species with V. ovalifolium being highest and V. parvifolium not germinating at all. Mortality was lower at pH 5. At pH 6, V. ovalifolium and V. membranaceum exhibited variation for growth while all other species suffered complete mortality.

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B.M. Cregg, M.W. Duck, C.M. Rios, D.B. Rowe and M.R. Koelling

We assessed variable chlorophyll fluorescence (Fv/Fm) and needle chlorophyll concentration of seedlings of Maccedonia fir (Abies borisii regis Mattfeld), subalpine fir [A. lasiocarpa (Hooker) Nuttall], Sakhalin fir [A. sachalinensis (Schmidt) Mast.], Siberian fir [A. sibirica (Lebed.)], and Veitch fir (A. veitchii Lindl.) grown under varying soil media pH. Soil media pH was modified using liquid flowable dolomitic limestone, resulting in five pH levels (3.4, 4.0, 5.4, 6.0, and 6.8). Increasing media pH significantly reduced Fv/Fm and needle chlorophyll concentration in all of the species tested. The effect of pH on photochemistry was due to depressed nutrient uptake of P, Mn, B, and Cu. Because photosynthetic quantum yield may be related to deficiencies of several elements affected by pH, Fv/Fm may serve as a criterion to select for improved pH tolerance. Among the species examined, A. veitchii and A. lasiocarpa were most tolerant of increased pH based on Fv/Fm and needle chlorophyll concentration.

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James F. Harbage and Dennis P. Stimart

Involvement of pH and IBA on adventitious root initiation was investigated with Malus domestica Borkh. microcuttings. The pH of unbuffered root initiation medium (RIM) increased from 5.6 to 7 within 2 days. Buffering with 2[N-morpholino] ethanesulfonic acid (MES) adjusted to specific pHs with potassium hydroxide prevented pH changes and resulted in a 2-fold higher root count at pH 5.5 compared to pH 7 or unbuffered medium. As pH decreased, lower concentrations of IBA were required to increase root counts. Colorimetric measurement of IBA in buffered RIM showed greater IBA loss and higher root count were associated with lower pH levels in all cultivars. This suggests that IBA loss from RIM depends on medium pH, which affects root count. Root count differences between easy-to-root through difficult-to-root cultivars were not consistent with amount of IBA loss from RIM. Cultivar differences in root count could not be explained solely by IBA loss from RIM.

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Vladimir Orbović, Diann Achor, Peter Petracek and James P. Syvertsen

Effects of air temperature, relative humidity (RH), and leaf age on penetration of urea through isolated leaf cuticles of `Marsh' grapefruit (Citrus×paradisi Macfad.) trees on `Carrizo' citrange (C. sinensis L. Osbeck × Poncirus trifoliata (L.) Raf. rootstock were examined. Intact cuticles were obtained from adaxial surfaces of `Marsh' grapefruit leaves of various ages. A finite dose diffusion system was used to follow movement of 14C-labeled urea from urea solution droplets across cuticles throughout a 4-day period. Within the first 4 to 6 hours after urea application, the rate of urea penetration increased as temperature increased from 19 to 28 °C, but there was no further increase at 38 °C. Increasing relative humidity increased urea penetration at 28 °C and 38 °C. Cuticle thickness, cuticle weight per area, and the contact angle of urea solution droplets increased as leaves aged. Cuticular permeability to urea decreased as leaf age increased from 3 to 7 weeks, but permeability increased in cuticles from leaves older than 9 weeks. Contact angles decreased with increased urea solution concentration on leaf surfaces that were 6 to 7 weeks old, but solution concentration had no effect on contact angle on cuticles from younger and older leaves. Changing urea solution pH from 8.0 to 4.0 could have an effect on the amount of urea penetrating the cuticle through the loss of urea from breakdown possibly due to hydrolysis. Results from this study define leaf age, environmental conditions, and formulation for maximum uptake of foliar-applied urea.