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Kathryn S. Hahne and Ursula K. Schuch

Velvet mesquite [Prosopis velutina Woot., Syn.: P. juliflora (Swartz) DC. var. velutina (Woot.) Sarg.] has become more popular in arid landscapes of the southwestern U.S., but little information on N requirements during the seedling stage is available. In addition to optimize growth of seedlings, minimizing N in runoff during production is an important consideration. Experiments were conducted to determine how biomass production and N leaching were affected first by different ratios of ammonium and nitrate N in sand culture and second by different N concentrations when seedlings were grown in two substrates. Mesquite seedlings produced the greatest biomass after 120 days when fertigated with a solution of 33 NO3 : 67 NH4 +. Loss of N through leachate was 40% greater when NH + 4 comprised two thirds or more compared to one third or none in the fertigation solution. Nitrogen in leachate was highest after 16 weeks of treatment, coinciding with the reduced growth rate of seedlings. The second experiment utilized either sand or commercial growing media and a fertigation solution of 33 NO3 : 67 NH4 +. Fertigation with 200 mg·L–1 N after 60 days in either substrate produced greatest biomass, while rates of 25, 50, or 100 mg·L–1 N produced about half of that biomass. With few exceptions, less N in either form was found in leachate when seedlings were grown in media and were fertigated with the two higher N rates compared to seedlings grown in sand at the two higher N rates. Plant morphology, biomass accumulation, photosynthate allocation, and the fate of N in the growing substrate and in leachate were strongly affected by the choice of growing substrate.

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Ursula K. Schuch and David W. Burger

Twelve species of woody ornamentals were grown in containers in Riverside and Davis, Calif., to determine plant water use and compare crop coefficients (Kc) calculated with reference evapotranspiration (ET) from local weather stations (ETcim) or atmometers (ETatm). Water use, Kcatm, and Kccim differed by species, location, and month of the year. Raphiolepis indica (L.) Lindl., Pittosporum tobira (Thunb.) Ait., Juniperus sabina L., and Photinia ×fraseri Dress. were the highest water users in Riverside and Arctostaphylos densiflora M.S. Bak., Juniperus, Cercis occidentalis Torr., and Pittosporum used the highest amount of water in Davis, when averaged over the 20-month study period. Rhamnus californica Eschsch., Prunus ilicifolia (Nutt.) Walp., and Cercocarpus minutiflorus Abrams. were among the lowest water users in both locations. Although plant water use fluctuated considerably between individual sampling dates, the relative ranking of species water use in each location changed very little over the study period. During periods of high winds, ETcim may not provide an accurate reference for container crops. Kc values fluctuated seasonally from as much as 1 to 4.7 for high water users, while values were stable for low water users and also for Buxus microphylla japonica Rehd. & E.H. Wils., an intermediate water user. During periods of low ET, especially in fall and winter, Kc values were artificially high and failed to correspond to the plants' low water use. Kc values for low water users seem to be useful to estimate water requirements over an extended period of time, whereas general Kc values seem to have limited value for plants with high water demand and need to be modified for different growth stages and growing locations.

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Darren L. Haver and Ursula K. Schuch

The objectives of this study were to determine 1) the minimum controlled-release fertilizer (CRF) rate and the lowest constant medium moisture required to produce the highest quality plants and 2) if this production system affected quality of these plants under two postproduction light levels. Two New Guinea impatiens (Impatiens sp. hybrids) `Illusion' and `Blazon' (Lasting Impressions Series) differing in salt tolerance were grown for 42 days with a CRF at three rates (3.3, 6.6, or 9.9 g/pot) and two medium moisture levels (low or high) without leaching. The high moisture level (tension setpoints of 1 to 3 kPa) and 6.6 g of CRF/pot produced optimum biomass. Low medium moisture (tension setpoints of 4 to 6 kPa) reduced leaf area, leaf number, leaf N content, root, stem, and leaf dry masses as CRF rate increased from low to high for `Illusion'. Similar results in `Blazon' were observed as CRF rates increased from 3.3 to 6.6 g. Biomass decreased no further at the high rate of 9.9 g/pot. Biomass increased in both cultivars under high medium moisture when CRF rates increased from 3.3 to 6.6 g. Biomass of `Illusion' decreased at 9.9 g/pot, although no symptoms of salt sensitivity were observed (i.e., leaf tip burn). `Blazon' maintained a similar biomass when amended with 9.9 or 6.6 g CRF/pot, although electrical conductivity (EC) in the medium was 5.9 dS·m-1 in the upper half and 4.1 dS·m-1 in the lower half of the medium at the end of production. Growth of `Illusion' responded more favorably to postproduction light levels that were similar to those of production regardless of treatment imposed during production. Similar biomass responses occurred for `Blazon' regardless of the postproduction light level.

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Ursula K. Schuch, Leslie H. Fuchigami, and Mike A. Nagzao

Floral initiation in coffee has been shown to be stimulated by short days in young plants, but the inductive stimulus for mature plants is still not clear. Experiments were conducted to determine whether floral initiation in immature and mature plants is promoted by short photoperiods, and delayed by long photoperiods. In a growth chamber study, 18-month-old coffee (Coffea arabica L. cv. Guatemalan) plants exposed to 8 hr photoperiods developed flower buds after 4 weeks, whereas no floral initiation was observed on the plants exposed to 16 hr photoperiods for ten weeks. Trees growing in the field were illuminated with incandescent light from midnight to 3:00 a.m. from July to December 1989. The control plants received no artificial light during the same time period. Night light interruption delayed flower initiation until the end of December on branches that were fully exposed to the light. On control trees, flower buds started to emerge at the beginning of November. These results indicate that in immature and mature coffee plants floral initiation is stimulated by short days, and delayed by long days.

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Ursula K. Schuch, Anita N. Miller, and Leslie H. Fuchigami

Dormant coffee (Coffea arabica L.) flower buds require water stress to stimulate regrowth. A xylem specific watersoluble dye, azosulfamide, was used to quantify the uptake of water by buds after their release from dormancy by withholding water. In non-stressed flower buds, the rate of water uptake was generally slower and variable. In stressed flower buds, the rate of uptake tripled from one day to 3 days after rewatering and preceded the doubling of fresh and dry weight of buds. Free, ester, and amide IAA levels of developing flower buds were measured by GCMS-SIM using an isotope dilution technique with [13C6] IAA as an internal standard. Throughout development, the majority of IAA was present in a conjugated form and the dominant form was amide IAA. The proportions of amide and free IAA changed rapidly after plants were water stressed until day 3, and preceded the doubling of fresh and dry weight. Correlation coefficients of 0.9, 0.7, and 0.7 (p<0.l) were found between auxin content and fresh weight, dry weight, and rate of water uptake, respectively.

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Ursula K. Schuch, John F. Karlik, and Charlene Harwood

Moisture loss from bare-root plants during postharvest handling and storage can have a significant impact on plant survival and growth during establishment. Three film-forming antitranspirants and hot wax were applied to bare-root roses (Rosa) packaged after harvesting from the field and before 13 weeks of –2C storage to determine effects on vegetative growth and flowering. Subsequently, during 15 days under simulated display conditions (22 to 32C), plants treated with hot wax resumed growth at the fastest rate compared to control or antitranspirant treatments. Hot-wax-treated plants remained at an advanced phenological stage compared to the other plants for 2 weeks following transplanting in the field. For the remaining 10 weeks of the experiment, vegetative growth and flowering development were similar for all treatments. More than 60% of the plants treated with hot wax developed moderate to severe cane damage and plant dieback. Less than 20% of the antitranspirant-treated plants were damaged. A laboratory experiment confirmed that hot wax treatment was most effective; it reduced weight loss from stem sections by 85% relative to the control. The other antitranspirants reduced weight loss by 27%.

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John F. Karlik, J. Ole Becker, and Ursula K. Schuch

The impending worldwide restrictions on the use of methyl bromide (MeBr) as a soil fumigant have prompted an intensive search for more-effective methods for delivering MeBr or replacement compounds. Although the majority of agrochemicals are applied in the solid phase or the liquid phase at ambient pressure and temperature, some chemicals, including certain soil fumigants such as MeBr, are gases under normal field conditions. Experiments were conducted to evaluate use of two types of commercial drip irrigation tubing to deliver gases to nontarped planting beds. Air moved through each tubing type immediately after burial; water was not necessary for inflation. Air was also able to move through 40 m of buried rigid drip tubing and through 90 m of buried flat tape that had been used for subsurface drip irrigation for more than 1 year. Mixtures of known ratios of propane and air were introduced into the buried tubing over several time intervals to evaluate gas movement from buried drip tubing into the surrounding soil matrix. Samples were collected from sets of three soil gas sampling tubes placed 15, 30, and 45 cm to the side of the buried tubing and at regular intervals along the length of the tubing, and propane concentrations were quantified by gas chromatography. Tubing lengths and run times affected the magnitudes and uniformity of propane concentrations. Results suggest gas-phase chemicals can be delivered via buried drip-irrigation tubing, but effective distances from the point of introduction will be limited by the low densities and viscosities of gases, and corresponding high rates of escape through tubing emitters.

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Cynthia B. McKenney, Amber Bates, Kaylee Decker, and Ursula K. Schuch

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Ursula K. Schuch, H. Brent Pemberton, and Jack J. Kelly

Five cultivars of bare-root rose plants were exposed to increasing periods of drying and after rehydration were grown in containers until flowering in a plastic-covered greenhouse. At the start of the experiment, moisture content of well-hydrated roses was between 51% and 56%. Five or 7 h of drying resulted in moisture contents below 43% for four of the cultivars and caused up to 80% mortality, increased time to flower, and decreased the number of flowering shoots. ‘First Prize’ was most tolerant of drying conditions and all plants survived, whereas ‘Mister Lincoln’ plants were most susceptible and had poor regrowth performance. Whole-plant moisture of ‘Mister Lincoln’ was similar to that in the stem or shank, which means that aboveground components instead of the entire plant can be used for moisture determination.

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Ursula K. Schuch, Leslie H. Fuchigami, and Mike A. Nagao

Unsynchronized flowering and fruit ripening of coffee prohibits mechanical harvesting and results in high labor costs. Coffee (C.arabica c. Guatemalan) trees were sprayed at the beginning of the 1988 and 1989 flowering season with solutions of benzyladenine (BA), gibberellic acid GA3 (GA), and Promalin (PR) or were pruned in 1988 to determine effects on synchronizing flowering and ripening. Growth regulators affected the time to flowering and harvesting compared to the control, however, treatment effects were dependent on the time of growth regulator application. Application of PR and GA at 100 mg/l in Jan 1988 shortened the average days to flowering by 16 and 13 days, and the average days to harvest by 15 days compared to the control. Pruning of three apical nodes of primary lateral branches in Feb 1988 caused delays in flowering, reduced flower and fruit number per tree, and caused branch dieback.