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- Author or Editor: Ursula K. Schuch* x
- HortScience x
Eight-week-old potted chrysanthemum (Dendranthema grandiflora Tzvelev. c. Ovaro) plants were treated with a soil drench of 0 or 2.5 mg uniconazole per liter and irrigated daily with 350 or 250 ml of nutrient solution. Plants were frequently water-stressed during their development. At the beginning of anthesis treatments were split and transferred to chambers with 20C/24 hr photoperiod or 25C/dark conditions. Anthesis progressed at the same rate in the two postharvest storage conditions, regardless of previous treatments. Plants were not watered until wilting, which was observed first in control plants under continuous photoperiod (8 days) and last in uniconazole-treated plants in dark storage (12 days). During the first 6 days in storage, evapotranspiration (ET) was lower for plants grown with 250 ml daily irrigation. From day 8 to day 12, when most plants were irrigated after they had wilted, ET was affected by uniconazole and an interaction of uniconazole and storage conditions.
The objective of this study was to determine whether mesquite (Prosopis velutina) seedlings have a preference for the ammonia or nitrate form of nitrogen (N), and to determine the optimum rate of N to maximize growth and minimize N leaching when seedlings are grown in different substrates. Mesquite seedlings were fertigated with different ratios of NH4 +: NO3 - to determine effects on shoot and root growth and N-uptake efficiency. Nutrient solution containing 67% NH4 + : 33% NO3 - resulted in greatest biomass after 120 days of fertigation. N leachate remained stable until 12 weeks after the onset of treatment, but increased significantly by week 16. Subsequently, mesquite seedlings were grown in sand or soilless media and were fertigated with a solution of 67 % NH4 +: 33% NO3 - at a rate of 25, 50, 100, or 200 mg·L-1 of N. After 60 days, plants in media produced 41% more leaves and total biomass compared to those in sand. Leaf number was greatest for plants grown at 200 mg·L-1 of N in both substrates. Root biomass of plants in media showed no response to increasing N concentrations while root biomass of seedlings in sand were similar for the three lower N concentrations and nearly doubled for the highest one. Shoot biomass of seedlings receiving 25, 50, or 100 mg·L-1 of N was similar, but more than doubled for plants fertigated with 200 mg·L-1 of N. N leachate losses were highest from seedlings growing in sand and receiving the two higher N fertigations, those in media had greatest N leachate loss when fertigated at 200 mg·L-1 of N. For balanced mesquite seedling growth and minimum N leaching losses, concentrations between 50 to 100 mg·L-1 of N are recommended. Implications of using a sand culture system vs. soilless growing substrate for nutrition studies will be discussed.
Rose (Rosa sp.) cultivars Blue Girl and Mister Lincoln were harvested bare-root on 1 Nov. 2001 and 22 Nov. 2002 from a commercial nursery in Arizona. Grade 1 plants were then potted and forced to flowering in either Tucson, Ariz., or Tyler, Texas. Total chilling hours were calculated as the number of hours that the plants were exposed to a temperature below 7 °C in the field and during shipping and cold storage. Data were recorded when the petals on the first flower beg an to reflex. Overall, the number of flowering shoots and plant performance was positively correlated to digging date, weeks of cold and total chilling hours received. Days from potting to flower were negatively correlated to weeks of cold storage and chilling hours. However, when the data were separated by location, the number of flowering shoots, the percentage flowering shoots, and plant performance was positively correlated to weeks of cold and chilling hours in Arizona, but was positively correlated to digging date in Texas. Days from potting to first leaf unfolding were recorded in Arizona only and were negatively correlated to weeks of cold storage and chilling hours. Days from potting to flower were negatively correlated to chilling hours at both locations and also to weeks of cold storage in Texas. The increase in chilling from two or four weeks of cold storage increased the number of flowering shoots and performance rating of plants forced in Arizona during both seasons, but only for the 2001 season in Texas. During the 2002 season in Texas, these responses were not influenced by cold storage, but were greater than those seen during the 2001 season. In Arizona, days from potting to flower were greater in 2001 than 2002, and decreased in response to cold storage in 2001, but not in 2002.
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.
Moisture loss from bare-root plants during postharvest handling and storage can have a significant effect on plant growth and survival during establishment. Three film-forming antitranspirants and hot wax were applied to bare-root roses packaged after harvesting from the field and before three months of cold storage to determine effects on vegetative growth and flowering. Subsequently, during three weeks under display conditions, plants treated with hot wax resumed growth at the fastest rate compared to control or antitranspirant treatments. Hot wax-treated plants continued to grow at a faster rate than the other plants for two weeks following transplanting in the field. For the remaining 10 weeks of the experiment no differences in vegetative growth or flowering development were found between treatments. Over 70% of the plants treated with hot wax became sunburned, resulting in severe cane damage and plant dieback. Less than 20% of the plants from the other treatments were damaged.
Poinsettia (Euphorbia pulcherrima `Gutbier V-14 Glory') were grown using commercially available poinsettia fertilizer of various combinations of controlled-release (CRF) and constant liquid fertilizer (LF). At the end of the production period, plants treated with 83, 165 or 250 mg/l LF only were 10% taller than plants treated with the same concentrations of CRF. The total number of cyathia and the number of open cyathia at harvest was 18% and 50% higher for plants treated with LF only compared to plants treated with CRF only. Plants treated with 165 CRF/ 83 LF or 83 CRF/250 LF were not different compared to 250 CRF/0 LF or 0 CRF/ 250 LF in height, number of cyathia at anthesis, and total number of cyathia at the end of the production period. When LF was changed to clear water 5 weeks before the end of production, nitrate runoff from 83 CRF/250 LF treatment was reduced 30% for the last two weeks, and from the 165 CRF/83 LF treatment nitrate leachate was reduced gradually from 33 to 66% over the 5-week period.
This study was designed to determine whether trees growing in tall, narrow containers versus regular containers of equal volume, or trees growing in containers coated with cupric hydroxide versus no coating would have a better quality root system, less circling roots, and more biomass production. Ficus (Ficur retusa L. `nitida') and pepper (Schinus terebinthifolius Raddi.) liners were grown for 6 months in the greenhouse in one-gal. containers. Cupric hydroxide coating prevented matting of roots on the side of the root ball in both species and root circling at the bottom of containers in ficus. Pepper trees growing in regular-shaped containers had a higher biomass production versus trees growing in tall containers. Subsequently, trees were transplanted to 3 or 5 gal. containers with shape or coating as described above. For pepper, cupric hydroxide coating versus no coating reduced circling and matting of roots, trees in regular versus tall containers had increased above ground biomass, and trees in 5-gal. versus 3-gal. containers grew more medium and small-sized roots and produced more total biomass.
High tunnels are unheated structures covered with polyethylene (PE) glazing to protect high-value crops from adverse weather. The objective of this study was to raise soil temperatures to determine the efficacy of soil solarization using clear mulch on the soil surface and glazing or no glazing on a high tunnel during the hottest months of the year in the semiarid southwestern United States. Solarization trials were conducted in May and June 2013 in two high tunnels in southern Arizona. Highest soil temperatures were reached with the combination of a high tunnel covered with glazing and the soil covered with PE mulch. Average daily soil temperatures were 48 and 47 °C and average degree hours (DH) per day (base temperature 45 °C) were over 14 at soil depths of 5 and 15 cm. The average daily maximum soil temperature at 5- and 15-cm depth was 63.4 and 52 °C, respectively. The second highest soil temperatures were reached when the soil was covered with PE mulch without high tunnel glazing, which resulted per day in 5.2 DH above 45 °C at 5 cm and less than one DH at 15-cm depth. Glazing on the high tunnel without covering the soil surface raised soil temperatures only at the 5-cm depth above 45 °C, but not further down. High tunnel producers in the low desert areas in the southwestern United States can complete solarization in less than 1 week, depending on the organism to be controlled, when the soil is fallow during the summer months with glazing on the high tunnel and on the soil surface.
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.
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%.