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Kent D. Kobayashi

The simulation programs Stella® (High Performance Systems) and Extend™ (Imagine That!) were used on Apple® Macintosh® computers in a graduate course on crop modeling to develop crop simulation models. Students developed models as part of their homework and laboratory assignments and their semester project Stella offered the advantage of building models using a relational diagram displaying state, rate, driving, and auxiliary variables. Arrows connecting the variables showed the relationships among the variables as information or material flows. Stella automatically kept track of differential equations and integration. No complicated programming was required of the students. Extend used the idea of blocks representing the different parts of a system. Lines connected the inputs and outputs to and from the different blocks. Extend was more flexible than Stella by giving the students the opportunity to do their own programming in a language similar to C. Also, with its dialog boxes, Extend more easily allowed the students to run multiple simulations answering “What if” questions. Both programs quickly enabled students to develop crop simulation models without the hindrance of extensive learning of a programming language or delving deeply into the mathematics of modeling.

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Xuewen Gong, Shunsheng Wang, Cundong Xu, Hao Zhang, and Jiankun Ge

for determining a scientific and rational irrigation schedule to improve water use efficiency ( Qiu et al., 2017 , 2019 ; Yan et al., 2017 ; Yuan et al., 2001 ). Establishing an ET c model is a simple method to get water requirements of crops, thus

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C. C. Pasian and J. H. Lieth

The main objective of this project was to develop a crop simulation model for greenhouse cut flower roses. An intermediate step towards the completion of that objective is the building of a model for the growth and development of a collection of shoots of various ages throughout the canopy. The canopy is represented as ten 20 cm thick layers. The shoot and leaves (age and location) are tracked as they grow into and through these layers using a model developed previously. Leaf area (LA) and leaf area index (LAI) for each layer is computed. A light distribution submodel, based on cumulative LAI, estimates the amount of radiation intercepted by each leaf. It is assumed that multiple shoots originating the same day from the same layer are identical. The model also simulates the effect of harvest of the shoots in the canopy. Currently, work is proceeding on data collection for prediction of carbohydrate partitioning within the canopy. Future work will focus on model validation.

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Hassan Zekki, André Gosselin, and Laurent Gauthier

24 ORAL SESSION 9 (Abstr. 078–085) Modeling & Statistics/Cross-commodity

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J.B. Reid, A.R. Renquist, A.J. Pearson, and P.J. Stone

Economic and environmental concerns have increased the need for quantitative advice on fertilizer rates. In addition, it would aid researchers to be able to estimate the degree to which nutrient availability is affecting yield in a wide variety of field experiments. All of these needs can, in principle, be addressed using the new PARJIB model. PARJIB retains the functional simplicity of much earlier analytical models of crop responses to soil test values and fertiliser application rates. However, in a key departure from previous approaches, response to scaled nutrient supply indices is dictated by the potential yield adjusted for plant population and water stress. The version currently being evaluated simulates responses to supply of N, P, K and Mg, varying either singly or in combination. We have calibrated the model for sweet corn, carrots, and snap bean crops grown under temperate conditions in a wide range of soils. Simulated yields agreed well with observed values; the root mean square error was 8% to 13%, and regressions of observed against simulated yields passed through the origin with slopes that were not significantly different from 1. After calibration, the model predicted strong interactions between nutrient supply, plant population and water stress. PARJIB appears to have substantial potential to improve nutrient management for horticultural crops.

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Robert D. Berghage, Alan Michael, and Mike Orzolek

Current and future plans for reductions in federal and state funding suggest that government supported programs must find ways to reduce costs while maintaining or expanding programs. The current model of extension, with an agent for each commodity in every county is not likely to survive. Furthermore, the days when university-based specialists could afford to make house calls also are probably limited. Yet, the need for extension support in the floriculture industry is as great as ever. Increased chemical costs and regulatory pressure are restricting grower options and making it increasingly important that information dissemination and technology transfer occur in timely and appropriate ways. To try to meet the needs of the floriculture industry in Pennsylvania, we have begun a program to help develop independent greenhouse crop management associations to work with milti-county and university-based extension specialists to improve program delivery to the member greenhouses. The first of these associations has been established in the Capital Region in central Pennsylvania and is providing IPM scouting and crop management services to member greenhouses. Development of associations and linkages with and the role of extension are discussed.

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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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Shaul Naschitz and Amos Naor

Water availability and crop load (number of fruit per tree) affect the fruit size of apple (Malus ×domestica Borkh.), but their interaction in relation to fruit size is not well understood. The objective of the present study was to explore the effect of crop load on water consumption of `Golden Delicious' apple in relation to fruit size. A wide range of irrigation rates and crop loads was applied to mature, field-grown `Golden Delicious' apple trees for two consecutive years, 1995 and 1996. The number of fruit, crop yield, and average fruit diameter were determined for each tree. A model was proposed to describe the combined effect of crop yield and irrigation rate on fruit size. In the model, irrigation waters were divided between two uses: vegetative water use (UV), which enables the tree to produce a steady, long-term yield; and reproductive water use (UR), which supports the production of the dry mass of commercial-size fruit. Potential fruit diameters were 77.1 and 72.2 mm for 1995 and 1996, respectively. Calculated vegetative use values were 300.2 and 323.4 mm for 1995 and 1996, respectively. The response of fruit diameter to reproductive water use per ton fresh weight (specific reproductive water use; URT) was fitted by a hyperbolic model in which the fruit diameter increases with increasing specific reproductive water use and approaches the yearly potential diameter at 60 to 70 m3·t-1, irrespective of the potential fruit diameter. In both years, fruit diameter showed a closer correlation with the specific reproductive water use than with either crop load or irrigation rate. In conclusion, the crop yield and the potential fruit size determine the irrigation rate required to achieve a certain average fruit diameter. The year's potential fruit diameter does not affect the total tree water use or its components. The proposed model can be used by growers for supporting decisions on irrigation and thinning strategies in commercial orchards.

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K.J. Boote and N.B. Pickering

. Goudriaan for their excellent suggestions for adapting the sunlit leaf area index approach for hedgerow canopies. We thank J. Norman for his advice on the model and E.B. Blazey and G. Bourgeois for their assistance with photosynthesis measurements. The cost

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James A. Poss, Christy T. Carter, Catherine M. Grieve, and Peter J. Shouse

Common stock flower production can be achieved under moderate levels of salinity and relatively low levels of nitrogen with no significant decrease in quality in a closed-recirculating irrigation system. A 4 × 4 factorial design with partial replication was used to assess the effects of salinity and nitrogen on the production of Matthiolaincana (L.). Seeds were sown in outdoor volumetric lysimeters at the George E. Brown, Jr., Salinity Laboratory in Riverside, Calif., with target electrical conductivity (EC) levels of 2, 5, 8, and 11 dS·m–1 combined with four nitrogen treatments of 35, 50, 75, and 100 ppm N. An empirical model was implemented to evaluate the growth response of each combination of salinity and nitrogen treatments over the course of plant development. The three-phase model is represented by an initial size parameter (alpha), an estimation of the intrinsic growth rate of the exponential phase (beta), a transitional phase between the first two phases (tl), the length of the linear phase (epsilon), and the final intrinsic saturation rate (gamma), The model successfully fitted the plant height data over time for all 16 nitrogen and salinity treatment combinations. Effects of salinity on epsilon and t2 (epsilon + t1) were nonsignificant. Nitrogen treatments had no significant effect on any of the model parameters and the effect of salinity was greatest when irrigation water EC was 11 dS·m–1. The length of the flower-bearing stems exceeded the standards recommended for commercial acceptability in all treatments (>41 cm). If 60 cm is the minimum length acceptable, then 50 ppm N or more where the EC was 8 dS·m–1 or less is required. Nitrogen uptake per unit evapotranspiration increased with salinity and nitrogen.