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L-Y. Li and J.H. Lieth

Greenhouse crop production involves high rates of energy input to implement a greenhouse microclimate that results in high productivity levels, correct crop timing, and desired product specifications. Producing quality crops while maintaining low energy consumption is achievable through improved crop management and environment control strategies. In this study, greenhouse crops and their microclimate were treated as an integrated system that was driven by solar radiation and external energy input. A set of simulation models were developed to describe the greenhouse climate, the crop, and their dynamic interactions. The temperature and light regimes were simulated using the greenhouse energy budget under typical weather patterns. The crop model simulated growth and development of several ornamental greenhouse crops. Coupling the crop model with the greenhouse energy model resulted in a system that allows determination of optimal strategies for crop management and environmental control. This greenhouse/crop system can be used to assist growers with formulating strategies of greenhouse production management.

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J.L. Robbins, X.Y. Li, and A.K. Yadav

Shoot tip explants from field-grown guava (Psidium guajava L.) trees, which frequently show a high rate of contamination, were cultured on the MS medium with neem leaf (Azadirechta indica L.) extract in H2O. Ten grams of neem powder prepared from crushed dried leaves was made to 200 mL aqueous solution and was left on a laboratory bench for 24 h. The amber-color neem extract was filtered to separate and discard solid. The liquid was refrigerated until needed. To 950 mL basic medium in deionized H2O containing 25 mL macronutrients, 5 mL micronutrients, 5 mL vitamins, 5 mL EDTA + Fe, 2 mL BA, 30 g sucrose, and 7 g agar, 50 mL neem extract was added either before or after autoclaving. No neem extract was added to the control. Medium was adjusted to 5.7 pH. Unused medium was refrigerated. Shoot tips from actively growing young twigs of field-grown L-49 guava trees that showed variable contamination in previous studies were harvested during midmorning hours. Samples were washed in running water and disinfected with 15% Clorox solution with few drops of Tween-20 for 15 min. There were 20 explants in each treatment. Explants were subcultured a week later. None of the four test studies showed contamination-free cultures from field trees. There was no consistency due to autoclaving neem extract. The neem leaf extract did not show complete elimination of contamination, although it delayed it for few days. It was concluded that neem extract was not effective at concentrations used in getting rid of contamination. Therefore, further investigate effect of neem for this purpose higher concentrations need to be examined.

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L-Y. Li, J.H. Lieth, R.H. Merritt, and H.C. Kohl

A heat-unit model was established for tracking the development of geranium, based on experimental data collected at UC Davis and Rutgers Univ. The temperature thresholds for initiating development and heat-unit benchmarks needed to accomplish each phenostage are parameters in this model. The methods of estimating these parameters were proposed and tested with the observed data. The model worked well during either vegetative or reproductive stages, but failed to predict the initiation of flowers, suggesting that factors other than only temperature drive the flower initiation process. With this model crop development characterized by a series of specific morphological events can be tracked and predicted under various temperature regimes, so that crop timing can be more precise.

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Z.L. He, D.V. Calvert, A.K. Alva, and Y.C. Li

Fertilization is among the most important factors influencing fruit quality of citrus. Effects of Individual element such as N, P, or K on fruit quality have been well-documented. Much less has been done on the interactions of N, P, and K in relation to citrus fruit quality. A field experiment was conducted from 1994 to 1999 in a commercial grove on a Riviera fine sand (Loamy, siliceous, hyperthermic Arenic Glossaqualf) to investigate the effects of fertilizer rates and sources on fruit quality of 26-year-old `White Marsh' grapefruit trees (Citrus paradisi Macfad.) on Sour Orange rootstock (Citrus aurantium Lush). Fertilizer was applied as water-soluble dry granular broadcast (three applications/year) at N rates of 0, 56, 112, 168, 224, and 336 kg/ha per year using a N;P:K blend (1.0:0.17:1.0). There was a quadratic relationship between fruit weight or peel thickness and fertilizer rates. Fruit weight per piece increased with fertilizer rates from 0 to 168 kg N/ha per year, but decreased from 168 to 336 kg N/ha per year. Fruit size was small at zero or low fertilizer rates due to nutrient deficiencies. Large fruit sizes of `White Marsh' grapefruit in the sandy soil were achieved at fertilizer rate around 168 kg N/ha per year. Increasing fertilizer application rates higher than 168 kg/ha per year greatly increased the number of fruit per tree, but decreased the size of fruit. Peel thickness, which is related to the fruit size, declines at higher fertilizer rates. Increase in fertilizer rate from 0 to 336 kg N/ha per year increased solids content and fruit acid concentration of the grapefruit. Fertilization rate effect on fruit Brix concentration was more complicated. Brix concentration was not affected by increasing fertilizer rates from 0 to 168 kg N/ha-per year, but was increased at higher fertilization rates (168 to 336 kg N/ha per year). As a result, the Brix/acid ratio was, in general, decreased by increasing fertilizer rates.

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J.H. Lieth, L.R. Oki, P. Ng, M.C. Garcia-Navarro, S.H. Kim, and L.-Y. Li

Daminozide is a growth retardant used in potted plant production as a foliar spray to inhibit shoot elongation. It has its greatest inhibitory effect immediately after application, becoming less pronounced thereafter; continued retardation is accomplished by reapplication at 7to 14-day intervals. A model for this retardation effect is useful in developing decision support tools, as well as in optimizing (perhaps minimizing) the use of this growth retardant. Such a model, as developed and described earlier, simulates the effect of a foliar spray application of daminozide at various concentrations on various days during the production cycle. The objective of this work was to validate this model for various varieties of chrysanthemum. Using the model to simulate the effect of one application of daminozide resulted in predicted plant heights very close to the observed heights for most of the varieties tested. Of four methods used to implement the multiple-application effect, two resulted in very good simulation of the observed plant heights. In summary, the model was shown to be valid for all the varieties of chrysanthemum tested.