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Patrick H. Brown

The aim of this research was to determine the seasonal patterns of N demand and uptake in mature almond trees and to use this information to develop an integrated computer model to guide fertilization management. To this end sequential whole tree excavations were conducted at 5 stages during a 15-month period. At each harvest date, five entire mature trees were excavated and partitioned into leaves, root, trunks, and branches. Samples were then analyzed for total nutrient content and differences in nutrient content between sequential harvests, which represents tree nutrient demand and tree nutrient uptake. Infromation on seasonal N uptake dynamics and total yearly N demand has now been integrated into a user-friendly interactive computer program that can be used to optimize N fertilizer management. The details of this program will be discussed. In summary, the determination of N fluxes in almond demonstrates that the majority of N uptake and demand occurs from late February through to early September and that the primary demand for N is for nut fill and nut development. N demands can therefore be predicted by estimating yield and can be applied during the periods of greatest N uptake from the soil which occurs during nut development. By timing N applications with periods of greatest demand, and matching N application rates with crop load we provide growers with a tool that will encourage maximum efficiency of use of N fertilizers. Maximum efficiency of use will result in a minimization of N loss from the orchard system.

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Niels Ehler, Mark A. Rose, and Jesper Mazanti Hansen

Currently, greenhouse environmental computers are programmed to monitor and control the macroclimate instead of directly controlling plant growth and development, which are features of more interest to growers. Our objective was to develop a generic system to represent and control the dynamic plant processes that regulate plant growth in the greenhouse. Before plant growth can be directly controlled, the dynamic interactions between the microclimate around plants and plant physiological processes must be further understood. Future computerized control systems must be able to display an intuitive, interactive software program that helps the user understand and make use of the dynamic relationships between climate controls, climate processes, and plant processes. A conceptual framework was designed for a user interface with a biological orientation. This software consists of five different elements: the information provider, the information monitor, the information browser, the growth system controller, and the system visualizer. A demonstrator application illustrating this concept was developed and connected in real time to a standard greenhouse environmental computer. Crop tissue temperature is calculated and used instead of conventional irradiance limits to control shading screens to optimize the amount of radiation absorbed by the crop. The application is based on a set of generic automatically created paradox databases. A graphical user interface on the screen displays virtual plants that are used for visualizing, understanding, and controlling the different processes governing the crop tissue temperature.

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Hudson Minshew, John Selker, Delbert Hemphill, and Richard P. Dick

Predicting leaching of residual soil nitrate-nitrogen (NO3-N) in wet climates is important for reducing risks of groundwater contamination and conserving soil N. The goal of this research was to determine the potential to use easily measurable or readily available soilclimatic-plant data that could be put into simple computer models and used to predict NO3 leaching under various management systems. Two computer programs were compared for their potential to predict monthly NO3-N leaching losses in western Oregon vegetable systems with or without cover crops. The models were a statistical multiple linear regression (MLR) model and the commercially available Nitrate Leaching and Economical Analysis Package model (NLEAP 1.13). The best MLR model found using stepwise regression to predict annual leachate NO3-N had four independent variables (log transformed fall soil NO3-N, leachate volume, summer crop N uptake, and N fertilizer rate) (P < 0.001, R 2 = 0.57). Comparisons were made between NLEAP and field data for mass of NO3-N leached between the months of September and May from 1992 to 1997. Predictions with NLEAP showed greater correlation to observed data during high-rainfall years compared to dry or averagerainfall years. The model was found to be sensitive to yield estimates, but vegetation management choices were limiting for vegetable crops and for systems that included a cover crop.

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. (covering duplication, postage, and handling). Send to: Gary Huntzinger, Rutgers Cooperative Extension, Office of Computer Services, P.O. Box 231, Blake Hall, New Brunswick, NJ 08903-0231 (phone 908/932-9279).

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M.B. Thomas, H.W. Beck, J.H. Crane, J.J. Ferguson, and J.W. Noling

A computer-based diagnostic system that can assist commercial producers, extension agents, and homeowners in the diagnosis of diseases, disorders, and pest damage for citrus, avocado, `Tahiti' lime, mango, carambola, lychee, and papaya was developed. The program was written in C++ and runs under MS-DOS. The system design was based on the diagnostic reasoning process of experts by identifying the location of symptoms, tree vigor, and occurrence within a grove. Full-screen color images link symptoms to possible diseases, disorders, and/or pest damage. Users can also refer to expert knowledge, graphic displays, pop-up menus, dialogue boxes, and retrieve information via hypertext from extension publications as well as current control methods. The program is available on CD-ROM, contains over 800 digital color images, and includes a glossary of terms.

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Eric H. Simonne, Joseph M. Kemble, and Doyle A. Smittle

A TurboPascal computer program was developed to calculate daily water budgets and schedule irrigations. Daily water use (di) is calculated as pan evaporation (Ep) times a crop factor (CFi), where i is crop age. The water balance uses a dynamic rooting depth, the soil water holding capacity (SWC) and rainfall data (Ri). di is added to the cumulative water use (Di-1) and Ri is subtracted from Di. An irrigation in the amount of Di is recommended when Di approximates allowable water use. The program cart be adapted to most crop and soil types, and can be used for on-time irrigation scheduling or for simulating water application using past or projected weather data. This program should increase the acceptance of modem scheduling irrigation techniques by farmers and consultants. Additionally, this program may have application in an overall water management programs for farms, watersheds or other areas where water management is required.

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Peter Havard, Leonard J. Eaton, and Peter R. Hicklenton

Two commercial freezers were modified to provide an inexpensive chamber system to investigate frost effects on wild, lowbush blueberries (Vaccinium angustifolium) under field conditions. A computer control system was developed with software written in Visual Basic 6.0 for MSWindows, which precisely controlled temperature in the plant canopy when the chambers were placed over blueberry plants in the field. Frost events (with temperatures ranging from -2 to -15 °C (28.4 to 5.0 °F)) were simulated by user input to control the cooling and warming rates, and minimum temperatures. The system records temperature set points, and current temperature in the plant canopy, or elsewhere in the plant environment, and provides a graphical display of key parameters. Trials have verified the reproducability of temperature profiles and the chambers have been used to provide preliminary information on the effects of frost at bloom on fruit set and development.

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Anthony W. Kahtz

The cognitive learning style theory of field dependence and independence was used to examine the academic achievement of students using a computer assisted instruction (CAI) program in a woody plant identification course. The Group Embedded Figures Test (GEFT) was used to determine the students' level of field dependence and independence. Students were blocked and randomly assigned to experimental or control groups. Participants in the experimental group used a nonlinear drill and tutorial type of CAI program as a partial laboratory substitute. The CAI program had no influence relative to traditional laboratories upon either field dependent or field independent students' long term memory of course material. However, the CAI program was of equal benefit to field dependent and independent students' academic achievement. Qualitative interviews were also conducted to assess the effect of the CAI program. Data indicated that field dependent students benefited from the CAI program as a presentation source of recall cues in the reviewing of course material, but not for the initial acquisition of knowledge. Field independent students may be able to use the CAI program to initially acquire knowledge, but its best usage may be as a method of presenting recall cues to refresh their memory. These results showed that the CAI program could be used as a partial laboratory substitute for traditional woody plant identification laboratories with no adverse effect upon student academic achievement, regardless of their level of field dependency.

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Josiah W. Worthington, James L. Lasswell, and M.J. McFarland

A computer model was used to predict irrigation rates and numbers of emitters or microsprayers required to trickle irrigate Redskin/Nemaguard peach trees. Irrigation rates were 0, 50%, and 100% of the predicted requirement based on a crop coefficient of 50, 80, 100, 80, and 50 percent of pan evaporation for the tree's canopy area for May, June, July, August and Sept. respectively. Full irrigation (100% of predicted) was applied through 6, 8L/hr emitters or one 48L/hr microsprayer. Half the predicted rate was applied through 6, 4L/hr emitters or 1 24L/hr microsprayer. Control trees received no supplemental irrigation. Microsprayers height was adjusted to wet a surface area comparable to the 6 emitters. There was no significant difference in fruit size or yield based on emitter vs microsprayers, but fruit size and total yield was increased in direct proportion to irrigation rate. There was no treatment effect on tree pruning weights. Moisture measurements indicated that trees de-watered the soil efficiently enough that water never moved below the 30 cm level in spite of the fact that up to 260 liters per tree per day were applied in mid-summer.

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C.A. Sanchez, T.M. Blackmer, G.E. Meyers, and J.S. Schepers

Lettuce (Lactuca Sativa L.) produced in the low desert typically shows large yield responses to N fertilization. Concern about the potential threat of nitrate-N to ground water prompted the state of Arizona to pass legislation aimed at implementing improved N management practices. Nitrogen management guidelines recommended by the University of Arizona for lettuce suggest a preplant application based on a soil nitrate-N test and subsequent sidedress applications based on plant tissue monitoring. However, growers have some anxiety that close adherence to recommendations resulting from an average plant sample may compromise crop uniformity. Aerial photographs have the potential to detect differences in N status in any portion of the field. This study evaluated digital computer analysis of aerial photographs as a tool for evaluating the N status of lettuce. The digitized photographs appeared to detect deficiencies not apparent to the human eye. There were good correlations (R2 0.83 to 0.99) between Gray-scale ratio and N status, suggesting digital analysis of aerial photographs has potential for diagnosing N deficiencies in lettuce.