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U.K. Schuch and D.W. Burger

Twelve species of woody ornamental plants were grown for 2 years in containers at Riverside and Davis, Calif., to determine plant water use (WU) and compare crop coefficients (Kcs). WU was determined gravimetrically in 1993 and 1994, five times each year in Riverside and four times each year in Davis. WU and Kc were affected by significant interactions among species, location, and time of year. WU was primarily influenced by the month, while Kc was most affected by location. Rhaphiolepis and Pittosporum, followed by Juniperus and Photinia, respectively, were the highest water users in Riverside when averaged over the 2 years. Arctostaphylos was the highest water user in Davis, followed by Juniperus, Cercis, and Pittosporum, respectively. Rhamnus, Prunus, and Cercocarpus were among the lowest water users in both locations. Heteromeles, Buxus, and Ceanothus were intermediate water users. The largest difference in species WU between the two locations was found for Arctostaphylos and Cercis, both high water users in Davis, but moderate or low water users in Riverside. The other species ranked similarly in both locations. Kcs of the 12 species, when averaged over the 2-year sampling period, ranked similar to water use. Kcs tended to be artificially high in the winter months and were not correlated to the low WU during that time.

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D.W. Burger, T.K. Hartz and G.W. Forister

Seed germination and crop growth characteristics were determined for Tagetes spp. L. `Lemondrop', marigold; Catharanthus roseus Don. `Little Pinkie', vinca; Petunia hybrida Vilm. `Royalty Cherry', petunia; Dendranthema×grandiflorum (Ramat.) Kitamura `White Diamond', chrysanthemum; Pittosporum tobira Ait. `Wheeleri', sweet mock orange; Photinia ×fraseri Dress., photinia and Juniperus sabina L. `Moon Glow', juniper grown in various size containers containing blends of composted green waste (CGW) and UC Mix. Seed germination, plant height, and stem and root fresh and dry mass were lowest in unamended CGW. For most plants studied, a CGW: UC Mix blend containing at least 25% UC Mix was required for adequate growth and development. Germinating seeds and young seedlings were most adversely affected by unamended CGW. As plants grew and were transplanted into larger containers (10- and 15-cm pots, 530 and 1800 mL), they were better able to grow in media with higher CGW content.

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J.L. Lyles, J.D. MacDonald and D.W. Burger

Roots of hydroponically grown Hibiscus Rosa-sinesis L. cuttings were exposed to 22, 30, 40, or 50C for 20 minutes, after which they were inoculated with zoospores of Phytophthora parasitica Dastur. Visual assessment of root discoloration and culturing of randomly selected root pieces 10 to 13 days after treatment showed that roots exposed to 40 or 50C had a significantly higher incidence of infection than those exposed to 20 or 30C. Plants were also grown in pots containing University of California (UC) mix or washed, graded sand and exposed to solar radiation for 1 day or 3 weeks, respectively. Root systems of plants in direct sunlight heated to 52C, while roots of shaded plants heated to 40C. Assessment of infection severity was done visually or by means of a Phytophthora-specific antibody probe. In all experiments, infection severity was highest in sun-exposed plants and was insignificant to moderate in shaded plants.

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M. Raviv, J.H. Lieth and D.W. Burger

Rose plants (cv. Kardinal, grafted on Natal Brier) were grown in UC mix (42% fir bark, 33% peat, and 25% sand) and in coir. Water tension in the media was maintained within a predetermined narrow range using electronic tensiometers. Whole plant net photosynthesis as a function of the water tension in the medium was determined and the results were later normalized to measured leaf area. Simultaneous measurements of metabolic heat and respiration rate were carried out on detached young (FW = 10-20 mg.) leaflet samples, using differential scanning calorimeter (model 4100, Calorimetry Sciences, Provo, Utah). Only a small amount of plant material is removed for analyses so the assay is essentially non-destructive for the whole plant. Physical characteristics of the media greatly affect the relationship between water tension and water availability to plants. At similar tension values, water availability is much lower in coir than in UC mix. The effects of water availability on net photosynthesis, metabolic heat rate, and respiration will be discussed in relation to their effect on productivity.

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P.A. Kiehl, J.H. Lieth and D.W. Burger

A computer-controlled drip irrigation system was used to implement three types of moisture regimes in the potting medium of container-grown chrysanthemum [Dendranthema × grandiflorum (Ramat.) Kitamura] plants: “constant” moisture tension treatments were maintained by setting low- and high-tension set-points to the same value; “variable” tension treatments were imposed by setting the low- and high-tension set-points to 2 and 7 kPa, respectively, “timed” irrigation consisted of irrigating once per day for a fixed (excessive) duration that resulted in fluctuations in tension ranging from O to 10 kPa. Constant moisture tension conditions in the range of 0.8 to 16 kPa showed decreasing fresh and dry weight patterns with increasing tension, decreasing average moisture content, decreasing amounts of applied irrigation solution, and, consequently, with decreasing amounts of nutrients applied. Plants grown under conditions where the moisture content fluctuated appreciably (variable and timed) tended to be larger than those grown within the narrow tension ranges (constant); for the latter, optimal plant growth occurred at the lowest tension (0.8 kpa) and highest average moisture content (71%). For fluctuating conditions, the control (with the widest fluctuations) had the highest dry weight growth. The variable tension treatments, while resulting in average moisture tensions of 4.4 to 4.9 kpa, resulted in plant growth similar to plants grown at constant low tension (0.8 to 1.6 kPa), rather than those grown at tensions between 4 and 5 kPa.

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J.H. Lieth, P.A. Kiehl, S.A. Tjosvold, G.B. Vogel and D.W. Burger

An irrigation system was developed to water container-grown ornamental plants so that soil moisture tensions could be continuously monitored and controlled. Operation of such a system has been shown to significantly reduce the amount of water which must be applied to produce high-quality potted chrysanthemums. This presentation will focus on modification of drip irrigation systems in commercial production environments to irrigate based on soil moisture tension. High-quality plants were produced in commercial trials with such systems. In all cases significant economic savings due to reduced fertilizer and water application were observed. Furthermore, the amounts of irrigation water run-off were significantly lower than in systems where irrigation was controlled manually or with timers.