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Mark A. Rose and John W. White

Temperature affects all major plant physiological processes. Traditional methods of controlling greenhouse temperatures use aerial sensors that do not monitor temperatures within each component of the soil-plant-atmosphere continuum.

Bench, pot, plant canopy, and aerial temperatures were monitored using thermocouples and thermistors processed by environmental computers during a wide range of greenhouse conditions. These include diurnal cycles of high and low solar radiation, night periods with and without artificial lighting, and various ventilation and heating conditions. Spatial temperature gradients of 10-22 °C were discovered during both day and night conditions. These spatial variations cause significant differences in average temperatures between and within benches over diurnal and even seasonal cycles.

Preliminary surveys of microclimatic variations that occur within the greenhouse experimental area are essential for choosing the proper experimental design. Continuous environmental monitoring during the experiment is necessary for interpreting experimental results.

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Mary Ann Rose and John W. White

`Celebrate 2' Poinsettias were grown for 8 weeks in a controlled-environment growth room until first signs of bract coloration. In growth stage I (GSI; weeks 1 through 4) low, medium, and high N rates (25, 75, and 125 mg N/liter, respectively) were applied by subirrigation (no leaching). Following floral induction [growth stage II (GSII), weeks 5 to 8], there were nine treatments: all possible combinations of the three N rates in GSI plus three rates (75, 125, and 175 mg N/liter) in GSII. Although >80% of shoot dry weight and >90% of total leaf area developed during growth GSII, reaching an acceptable plant size by week 8 depended on receiving adequate fertilization in growth GSI. In contrast, leaf chlorosis, noted in plants receiving the lowest rate in GSI, was rapidly reversed by increasing the N rate in GSII. Quadratic regression equations fitted to shoot dry weight and leaf area data predicted that using 125 mg N/liter in both growth stages gave maximum responses at week 8. However, using 75 mg N/liter in GSI and 125 mg N/liter in GSII also produced acceptable growth in poinsettias. Our results suggest that some growth restriction imposed by N availability during the first 4 weeks of growth may be acceptable and perhaps desirable to reduce growth regulator use and the environmental impact of overfertilization.

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Mark A. Rose, John W. White and Joel L. Cuello

Recently developed stem flow gauges that allow for direct, accurate, non-invasive, and continuous measurement of plant sap flow rates have not been used to monitor transpiration of floricultural plants grown in greenhouses.

A Dynamax SGA10 heat-balance sap-flow sensor was mounted on a potted rose plant's main stem containing a total leaf area of 0.52 m in order to monitor transpiration. The sensor was connected to a CR21X Micrologger for data calculation and temporary storage. The results showed average midday sap-flow rates range from 20-30 g·hr-1 to 50-70 g·hr-1 at low and high levels of PPF, respectively. Nighttime levels of 4-7 g·hr-1 persisted throughout early winter trials. Monitoring transpiration of the same rose stem using a lysimeter revealed a significant linear correlation (r2 = 0.999) between the lysimeter and the stem flow gauge values.

In the future, research will be conducted with the gauge to investigate relationships between microclimatic variables, photosynthesis, and transpiration.

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Xuri Zhang, David J. Beattie and John W. White

Commercially cooled bulbs of five genetically dwarf Asiatic hybrid lilies were stored frozen at -2 C. Every 4 weeks for a total of 40 weeks, they were potted and forced in controlled environment chambers at 10, 15, 20, or 25 C. For each temperature, days from the time of potting to shoot emergence, visible bud appearance, and anthesis generally decreased as storage time increased. The number of flowers per plant and plant height were not significantly affected by storage time. Compared with those at 15, 20, or 25 C, plants at 10 C required significantly more time from potting to shoot emergence, visible bud, and anthesis. However, the temperature effects on forcing time were not linear. There was a 30-50 day decrease from potting to anthesis when temperature was increased from 10 to 15 C, but there was only a decrease of about 10 days when temperature was increased from 15 to 20 C. In contrast, there was no significant difference in forcing time between plants at 20 and 25 C. This indicates there is no need to force these lilies above 20 C. Plants at 25 C had more aborted flower buds than those at 10, 15, or 20 C. Plants at 10 C were taller then those at 15, 20, or 25 C.

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Mark A. Rose, David J. Beattie and John W. White

Two distinct patterns of whole-plant transpiration (WPT) were observed in `Moonlight' rose (Rosa hybrida L.) using an automated system that integrated a greenhouse climate computer, a heat-balance sap-flow gauge, an electronic lysimeter, and an infrared leaf temperature sensor. One pattern consisted of a steady rate of transpiration in a stable greenhouse environment. The second pattern consisted of large oscillations in transpiration unrelated to any monitored microclimate rhythms. These oscillations had a sine-wave pattern with periods of 50 to 90 minutes and ranged from 2 to 69 g·h-1 in natural light and 3 to 40 g·h-1 under high-pressure sodium lamps at night. Leaf-air temperature difference (T1 - Ta) also oscillated and was inversely related to transpiration rate. Oscillatory transpiration has not been reported in roses. Plant scientists need to recognize the complex and dynamic nature of plant responses such as the oscillatory pattern of WPT monitored in Rosa hybrida when selecting monitoring and control strategies.

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Allyson M. Blodgett, David J. Beattie and John W. White

Impatiens wallerana `Accent Red' were grown in a peat : perlite : vermiculite (PPV) or bark : peat : perlite (BPP) medium amended with SuperSorb-C (SS) or Soil Moist (SM) hydrophilic polymer and/or AquaGro-G (AG) wetting agent. In PPV or BPP, neither SS nor SM significantly increased shoot dry weight. In PPV, quality ratings were higher for plants grown in nonamended or SS- or SM- amended medium than for plants in AG-amended medium. In BPP, quality ratings were highest for plants grown in nonamended, AG-, or SM + AG-treated medium. Number of days from final irrigation to permanent wilting point (PWP) was greater in AG, SS + AG, or SM + AG treatments in PPV than in control, SS, or SM treatments, due to smaller plants in AG-amended media. In both media, root dry weight was not significantly greater with the use of either hydrophilic polymer or wetting agent. However, in PPV, AG suppressed root growth compared to the control.

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Mary Ann Rose, John W. White and Mark A. Rose

`Celebrate 2' poinsettias (Euphorbia pulcherrima Willd.) received either a constant application rate of 200 mg N/liter or a variable rate that was linked to the N accumulation pattern of the crop. At final harvest, shoot N content, N concentration, dry weight, leaf area, and quality were similar for the treatments. However, N recovery efficiency of the variable treatment was greater (58% vs. 38%), and 41% less total N was applied compared to the constant-rate treatment. Growth analysis revealed that N accumulation rates for both treatments increased rapidly as side branches developed, reaching a maximum 50 to 60 days after potting, and decreased throughout bract development. The decrease in N accumulation rates after day 60 reflected a shift in N allocation from leaves to bracts, a tissue with a lower N concentration.

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Jeffery C. Kallestad, Theodore W. Sammis, John G. Mexal and John White

Optimal pecan (Carya illinoiensis) production in the southwestern United States requires 1.9 to 2.5 m of irrigation per year depending on soil type. For many growers, scheduling flood irrigation is an inexact science. However, with more growers using computers in their businesses, and with soil moisture sensors and computerized data-collection devices becoming more inexpensive and accessible, there is potential to improve irrigation and water use efficiencies. In this project two low-cost soil monitoring instruments were introduced to a group of pecan producers. They were also given instruction on the use of Internet-based irrigation scheduling resources, and assistance in utilizing all of these tools to improve their irrigation scheduling and possibly yield. The objectives were to determine whether the technology would be adopted by the growers and to assess the performance of the sensors at the end of the season. Three out of the five growers in the project indicated they used either the granular matrix (GM) sensors or tensiometer to schedule irrigations, but compared to the climate-based irrigation scheduling model, all growers tended to irrigate later than the model's recommendation. Graphical analysis of time-series soil moisture content measured with the GM sensors showed a decrease in the rate of soil moisture extraction coincident with the model's recommended irrigation dates. These inflection points indicated the depletion of readily available soil moisture in the root zone. The findings support the accuracy of the climate-based model, and suggest that the model may be used to calibrate the sensors. Four of the five growers expressed interest in continued use of the tensiometer, but only one expressed a desire to use the GM sensor in the future. None of the participants expressed interest in using the climate-based irrigation scheduling model.

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Allyson M. Blodgett, David J. Beattie, John W. White and George C. Elliott

A plantless system using subirrigation was developed to measure water absorption and loss in soilless media amended with hydrophilic polymers, a wetting agent, or combinations of these amendments. Peat-perlite-vermiculite and bark-peat-perlite controls achieved 67% and 52% of container capacity, respectively, after 20 daily irrigation cycles. Maximum water content of amended media was 78% of container capacity. Adding only a hydrophilic polymer did not increase total water content significantly. Adding a wetting agent increased water absorption in both media. However, when hydrophilic polymer and wetting agent were present, the medium absorbed more water than with wetting agent alone. More extractable water was removed from media containing wetting agent. Water loss rate by evaporation was not affected significantly by medium, hydrophilic polymer, wetting agent, or any combination of these variables.