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Mark V. Yelanich, James E. Faust, Royal D. Heins, and John A Biernbaum

The measurement of evaporation and transpiration from container-grown crops is labor intensive and expensive if measurements are made by periodic weighing of the plants with electronic scales. Thin-beam load cells (LCL-816G, Omega Engineering) measured with a datalogger provides a method of making continuous mass measurements over time. Four load cells were tested to determine the feasibility for use in greenhouse studies. The sensors were calibrated to an electronic scale at a range of air temperatures. The electrical signal (μV) was a linear function of mass from 0 to 816 g. The change in mass per change in electrical signal (i.e. the slope) was the same for all four load cells (1.26 g ·μV-1), however the absolute electrical signal (the intercept) was unique for each sensor (-246 to + 101 g). The effect of temperature on sensor output was unique for each sensor in terms of both the magnitude and direction of change. A two-point calibration of mass performed at a range of temperatures is required to properly use thin-beam load cells to continuously measure evapotranspiration of container-grown crops.

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Thayne Montague*

Granier style thermal dissipation probes (TDP) have been used to estimate whole plant water loss on a variety of tree and vine species. However, studies using TDPs to investigate water loss of landscape tree species is rare. This research compared containerized tree water loss estimates of three landscape tree species using TDPs with containerized tree water loss estimates as measured by load cells. Over a three-year period, established, 5.0 cm caliper Bradford pear (Pyrus calleryana `Bradford'), English oak (Quercus robar), and sweetgum (Liquidambar styraciflua `Rotundiloba') trees in 75 L containers were placed on load cells, and water loss was measured for a 60-d period. One 3.0 cm TDP was placed into the north side of each trunk 30 cm above soil level. To reduce evaporation, container growing media was covered with plastic. Each night, plants were irrigated to soil field capacity and allowed to drain. To provide thermal insulation TDPs and tree trunks (up to 30 cm) were covered with aluminum foil coated bubble wrap. Hourly TDP water loss estimates for each species over a three-day period indicate TDP estimated water loss followed a similar trend as load cell estimated water loss. However, TDP estimates were generally less, especially during peak transpiration periods. In addition, mean, total daily water loss estimates for each species was less for TDP estimated water loss when compared to load cell estimated water loss. Although TDP estimated water loss has been verified for several plant species, these data suggest potential errors can arise when using TDPs to estimate water loss of select landscape tree species. Additional work is likely needed to confirm estimated sap flow using TDPs for many tree species.

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Amanda Bayer, John Ruter, and Marc W. van Iersel

each replication, plant height, number of internodes, internode lengths, stem diameter, and number of leaves were measured. The weight of each plant was measured using individually calibrated load cells (LSP-10; Transducer Techniques, Temecula, CA

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Lucas O’Meara, Matthew R. Chappell, and Marc W. van Iersel

allowed to drain for 15 min before being placed in growth chambers. Plants were randomly assigned to a load cell and growth chamber location with three load cells within each growth chamber. Plant weight was measured every 10 s using individually

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Lucas O’Meara, Marc W. van Iersel, and Matthew R. Chappell

; Campbell Scientific). The mass of a subset of eight plants, four of each species, was measured using eight individually calibrated load cells (LSP-10; Transducer Techniques, Temecula, CA) mounted on steel baseplates with the same 6.0-L containers mounted to

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Troy M. Buechel, David J. Beattie, and E. Jay Holcomb

A characteristic problem with peat moss is its difficulty in initial wetting and rewetting, especially in a subirrigation system. Wetting agents improve wetting characteristics primarily by reducing the surface tension of water. This results in a rapid, uniform movement of water by capillary rise through the growing medium.

Two methods were used to compare the effectiveness of different wetting agents: gravimetric and electrical. Ten cm pots containing peat moss were placed in a subirrigation system. The gravimetric method used a laboratory scale where pots were periodically weighed to determine the amount of water absorbed. The electrical method utilized thin beam load cells, which have strain gages bound to the surface, to determine the weight of a suspended object. Load cells were coupled with a Campbell Scientific datalogger to collect data every minute without removing the pot from subirrigation. Because the effect of buoyancy altered the true weights, equations were generated to adjust the water uptake values. Corrected weights were used to create absorption curves for comparison of the slopes to determine which wetting agent has the fastest rate of absorption. The load cell reliably and accurately described the wetting characteristics of Peat moss and we found good agreement with the gravimetric method.

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Tarja Hietaranta and Minna-Maria Linna

The firmness of five strawberry (Fragaria×ananassa Duch.) varieties was determined by penetrometric method using a motorized materials testing device equipped with a 100-N load cell and a probe 6.4 mm (0.252 inches) in diameter. Maximum and mean forces and instant of yield point were recorded with the aim of testing the suitability of these three parameters for the assessment of fruit firmness, i.e., handling and transportation tolerance. The maximum and mean force data revealed significant differences among varieties, but instant of yield point was not reliable measurement in this test arrangement. Maximum force was the best parameter for the assessment of firmness.

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Tiangen Wang and Stephen K. O'Hair

Concerns relating to pollution from nitrogen fertilizers leaching into ground water are increasing. This is especially important in southern Florida because the pollution threatens fragile ecosystems in Biscayne Bay, and the two National Parks that abut agricultural areas. The current research is focused on the development of an automatic system which can monitor \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document} and \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\) \end{document} leaching from plant nursery pots. \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document} and \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\) \end{document} electrodes and a load cell were used for real-time measurements of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document}, \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\) \end{document}, and leachate volume. The leachate was directed to pass the sensing areas of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document}, reference, pH, and \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\) \end{document} electrodes. It was collected and weighed in a container placed on a load cell. The analog signals from the electrodes and load cell were digitized through data acquisition technology using a 16-bit A/D converter and a self-developed software program. With this system the volume of the leachate and concentrations of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document} and \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\) \end{document} in the leachate were determined in situ. Based on this design, the dynamics of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document} and \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\) \end{document} leaching from pots can be observed. This system can be used to 1) determine soil (or media) holding capacity of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document} and \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\) \end{document}, 2) evaluate the effects of nitrogen fertilizer formulations on water quality, 3) develop best management practices of nitrogen application in containerized plant production, and 4) determine the soil-holding capacity to optimize the use of water. The advantages of the developed system are 1) low labor cost for sample collection and analysis and 2) high measurement resolution resulting from a minimization errors that occur during sampling and other manual operations.

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Craig A. Storlie and Paul Eck

Inexpensive weighing lysimeters ($1475/unit) were constructed for measuring evapotranspiration of young highbush blueberries (Vaccinium corymbosum L.). The use of a single load cell and other design characteristics decreased lysimeter measurement accuracy but minimized lysimeter construction costs. Measurement error was within ±3%. Crop coefficient (CC) curves for 5- and 6-year-old `Bluecrop' highbush blueberry plants in their third and fourth year of production were generated using reference evapotranspiration and crop water use data from the 1991 and 1992 growing seasons. The CC increased during leaf expansion and flowering in the spring to its maximum value of about 0.19 in 1991 and 0.27 in 1992 and remained near these values until leaves began senescing in the fall. Water use on sunny days during June, July, and August ranged from (liters/bush each day) 3.5 to 4.0 in 1991 and 4.0 to 4.5 in 1992. During the second year of the study, plants had an average height of 0.9 m, an average diameter of 0.9 m, and covered 18% of the total cultivated area. The maximum calculated CC was equal to 1.5 times the measured canopy cover percentage.

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D.A. Devitt, R.L. Morris, and D.S. Neuman

A 2-year study was conducted to quantify the actual evapotranspiration (ETa) of three woody ornamental trees placed under three different leaching fractions (LFs). Argentine mesquite (Prosopis alba Grisebach), desert willow [Chilopsis linearis (Cav.) Sweet var. linearis], and southern live oak (Quercus virginiana Mill.) (nursery seedling selection) were planted as 3.8-, 18.9-, or 56.8-liter container nursery stock outdoors in 190-liter plastic lysimeters in which weekly hydrologic balances were maintained. Weekly storage changes were measured with a portable hoist-load cell apparatus. Irrigations were applied to maintain LFs of +0.25, 0.00, or -0.25 (theoretical) based on the equation irrigation (I) = ETa/(1 - LF). Tree height, trunk diameter, canopy volume, leaf area index, total leaf area (oak only) and dry weight were monitored during the experiment or measured at final harvest. Average yearly ETa was significantly influenced by planting size (oak and willow, P ≤ 0.001) and leaching fraction imposed (P ≤ 0.001). Multiple regressions accounting for the variability in average yearly ETa were comprised of different growth and water management variables depending on the species. LF, trunk diameter, and canopy volume accounted for 92% (P ≤ 0.001) of the variability in the average yearly ETa of oak. Monthly ETa data were also evaluated, with multiple regressions based on data from nonwater-deficit trees, such that LF could be ignored. In the case of desert willow, monthly potential ET and trunk diameter accounted for 88% (P ≤ 0.001) of the variability in the monthly ETa. Results suggest that irrigators could apply water to arid urban landscapes more efficiently if irrigations were scheduled based on such information.