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Silvia Burés, Franklin A. Pokorny, David P. Landau, and Alan M. Ferrenberg

A FORTRAN computer program was developed to simulate packing of spherical particles via a Monte Carlo procedure. Shrinkage in volume upon mixing different particle sizes was studied and simulated results were compared with experimental data. Maximum experimental shrinkage was obtained when the proportion of coarse particles of pine bark and sand mixtures ranged from 50% to 70% of the volume. Experimental shrinkage of a mixture of coarse and fine sand was closely reproduced by means of simulation. Particle size distribution appears to be the most important factor in relation to shrinkage and also in the establishment of relationships between the simulated and the experimental system.

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Rico A. González, Daniel K. Struve, and Larry C. Brown

An irrigation control system has been developed and used to estimate evapotranspiration of contamer-grown plants by monitoring randomly selected plants within a container block and watering on an “as needed” basis. Sensor reliability and operational ease allows application of the system in a wide variety of field conditions. First-year tests, using red oak (Quercus rubra L.) seedlings, showed a reduction of 95% or better in both total irrigation and leachate rates with the computer-controlled treatment relative to a manually controlled, drip irrigation treatment without reducing plant growth.

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Arlie A. Powell and Karl Harker

It is always challenging to develop innovative Extension programs delivery methods. The development of a winter chilling model (Modified 45) for Alabama, the evaluation of a growth regulator (Dormex—hydrogen cyanamide) to replace lack of chilling in peaches and the establishment of a computerized weather program allowed us to create a superior expert program for grower application. Access through a personal computer is all that is required to monitor chilling accumulation and determine the most ideal time for application of Dormex (which is very critical). This information (formerly available from NWS) is now accessible through a private weather firm. The development of a chilling hour/heat unit (growing degree hour) for peaches is showing promise of providing growers still another useful product (via their PCs) in improving orchard management via better timing of practices.

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Steven E. Woerner and Douglas A. Hopper

A computer simulation model was developed to be used in evaluating irrigation scheduling techniques and assisting irrigation scheduling decisions under greenhouse conditions in Colorado. The model simulates variable greenhouse conditions and shows how each of four irrigation scheduling techniques responds to these conditions. Reports from the model detail numbers of irrigation events, sensitivities to parameters, and forecasts water usage. The model was also used to determine appropriate accumulation triggers for Colorado conditions.

Four techniques evaluated here include: time clock control; accumulated radiation; accumulated vapor pressure deficit; combination method (radiation and vapor pressure deficit). The model has shown the combination method to be the most sensitive to changes in environmental conditions, while the time clock method proved to be least sensitive (and most wasteful of water).

The model may evaluate additional irrigation scheduling techniques by including additional parameters in the model, and may readily be adapted to different climatic regions.

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Edward F. Gilman

Due to the high cost of color separations, few plant materials texts have photographs and line drawings showing each plant at different times of the year and at different ages. CD-ROM computer technology allows the user ready access to this information at a reasonable cost. Horticulturists at the University of Florida have developed three CD-ROM discs for use throughout the U.S. The discs contain more than 3000 pages of text, extensive morphological characteristics and plant use suggestions, in addition to more than 2000 line drawings and nearly 3600 photographs of more than 1,800 plant species. Software developed for DOS and Windows allows the student to generate customized plant lists for landscape sites. Lists can be created to match specific site characteristics, desirable ornamental attributes, or both. Students can also use the programs to help identify unknown plant specimens. Other features allow viewing of insect and disease problems and access to up-to-date control recommendations.

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Royal D. Heins and Paul Fisher

Height control is a major challenge in the production of high quality poinsettia crops. Graphical tracking is a technique where growers make height control decisions by comparing actual measured plant height with a desired height. A computer decision support tool, the Poinsettia Care System, is being developed to combine graphical display of plant height with an expert system to provide height control advice. A simulation model is used to predict future growth of the crop based on greenhouse temperature, growth retardant applications, plant spacing, plant maturity, and light quality. Growth retardant and temperature recommendations are made based on a crop's deviation from the target height, expected future growth rate, and crop maturity. The program was beta tested by 8 Michigan growers over the 1991 poinsettia season. The test growers reacted positively to the program in a follow-up survey. Perceived benefits included improved height control, consistent crop recording, and a `second opinion' when making height control decisions. Improvements were suggested to combine the advice of different crops within the same greenhouse zone, to improve the predictive growth model, and to streamline data entry and output.

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Robert Augé

The determination of tissue water potential components is important for understanding plant growth and response to the environment. Pressure-volume (PV) analysis is often considered to give the most accurate estimate of symplastic osmotic potential. Additional information about tissue water relations can also be computed from PV curves estimates of bulk cell wall elasticity, symplastic water volume, and turgor potential at various states of tissue water content. The generation of PV curves is a time-consuming procedure, however, and involves considerable computation. This presentation describes a computer spreadsheet template for traditional evaluation of a PV curve through linear regression of the zero turgor segment. The template allows real-time plotting of the inverse ψ/ water loss relating, provides estimates of most commonly calculated PV characteristics and permits instant graphic visualizations of changes in water potential components and elasticity with changes in water potential, total tissue water and symplastic water content. The advantages of spreadsheet analysis of PV curves are simplicity, consistency, thoroughness and speed. A fleeting acquaintance with spreadsheet software and a thorough understanding of pressure-volume theory on the part of the user is assumed.

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Mona R. Corbett, Christine D. Townsend, and Jayne M. Zajicek

Plant identification is a prerequisite to many, if not all, horticulturally related classes. It typically has been taught through the use of live specimens, slides, and text books. Recently, computers have entered the picture as a possible tool to teach plant identification. Increased availability and sophistication of computer systems in the college setting have led to the increased use of computers in instruction.

The objective of this study was to determine if there was a relationship between a student's learning style and academic achievement following computer assisted instruction. Undergraduate students enrolled in a plant identification class were involved in the study. Students learned plant identification either by: 1) viewing live specimens, 2) utilizing a computer instruction database system, or 3) combining live specimens with computer instruction. The students' cognitive knowledge was evaluated with pre and post tests. Learning style and attitude toward computer assisted instruction were also obtained.

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Lauren E. Howell and Michael N. Dana

A mail survey was conducted to determine attitudes held by garden center owners/managers about computers as customer-interactive marketing tools. The survey was sent to 220 garden centers in the 7-state North Central Region (IA, IL, IN, MI, MN, OH, WI), who were members of the Garden Centers of America. A response of 46% was received. Ownership of one or more computers was reported by 64% of respondents. Over 50% said they believe there is a place in garden centers for customer-interactive computer usage. Of those who did not agree that there is a place for point-of-sale computer usage in the garden center, the two most common objections were the impersonal nature of computers, and the cost. Survey results will contribute to development of perennial flower garden design software for use in point-of-sale marketing.

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Craig McFarlane and Thomas Pfleeger

Chambers were developed to study the uptake, accumulation and phytotoxicity of environmental pollutants. Each is connected to the computer and other support facilities by quick connects which allow the laboratory to be configured in various ways depending on experimental design. Each chamber consists of two isolation compartments connected only by plant stems. Electronic instruments are used to monitor key physiological processes of both the roots and shoots during the course of plant exposure. The computer controls the exposure conditions (i.e. day length, temperature, nutrient pH, CO2 concentration, etc.) as well as continuously collects information about plant responses (i.e. photosynthetic and transpiration rates). Photosynthesis, transpiration, and mineral nutrient uptake can be individually controlled by manipulating the environment and thus allowing their study in combination with additional stressors. The computer used to accomplish these tasks will be discussed along with other examples of computer use for plant manipulation.