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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.H. Lieth and C.C. Pasian

A mathematical description for the relationship between the rate of rose (Rosa hybrida L.) leaf net photosynthesis and photosynthetically active radiation, leaf temperature, and leaf age is developed. The model provides a tool for the prediction of these rates for leaves growing in a rose crop canopy.

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C. C. Pasian and J. H. Lieth

Temperature affects the rate of rose shoot development. In this study heat units were used to quantify “physiological age”. The objective was to determine whether rose shoots require the same number of heat units to reach various stages regardless of climatic conditions. The dates of occurrence of “bud break” (BB), unfolding of each leaf, “visible flower bud” (VFB), and harvest (H) were observed for 126 shoots of 'Cara Mia' roses growing under 5 different temperature and light regimes. Average air temperature (T) and photosynthetic photon flux density (PPFD) levels were recorded hourly. Heat units, defined as the sum of the difference T-Tb (units: °C hr-1) where Tb is the base temperature, were found to be a suitable for tracking most phases of rose crop development. The duration of the phase from H to BB showed considerable variation and thus could not be predicted this way. The duration from BB to VFB or H could be predicted reasonably well to occur at 5900 ± 670 and 12300 ± 1000 °C hr-1 (Mean ± Std. dev.), respectively, assuming Tb =6 °C. The occurrence of unfolding of each leaf can be predicted similarly. PPFD integrals had no significant effect on any development rates.

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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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C.C. Pasian and H.J. Lieth

Temperature effects on the rate of flowering rose shoot development were previously modeled using a thermal units (heat units) approach. The current objective was to validate this model for three rose cultivars and to determine its suitability for use in rose production. Flowering shoots of `Cara Mia', `Royalty', and `Sonia' plants, grown in greenhouses at three temperature settings, were observed daily to determine when each of the following developmental events occurred: “harvest”, “bud break”, “unfolding of each leaf”, “visible flower bud”, and “shoot ready for harvest”. Each stage was defined to facilitate accurate, repeatable observations. Average hourly air temperatures were used in computing the accumulated thermal units (TU) required for shoots to develop from from one stage to the next. The base temperature (used in the TU computation) did not differ significantly among the cultivars; the value of 5.2C was used. Using these to predict the days on which the shoot was ready for harvest resulted in ±2 day accuracy for most shoots of `Royalty' and `Sonia' and ±2.5 days accuracy for most `Cara Mia' shoots. This indicates that this method is suitable for timing of rose crops and deciding on temperature set-points.

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J. Steininger, C.C. Pasian and J.H. Lieth

`Candy Sunblaze' and `Red Sunblaze' miniature roses (Rosa L. sp.), were grown at several temperatures. The phenological events of budbreak (BB), visible flower bud (VB), and open flower (OF) were recorded daily. Based on these events, phenophases from BB to VB (BB:VB), from VB to OF (VB:OF), and from BB to OF (VB:OF) were defined. Daily rates of development to complete a phenophase increased with temperature between 13.6 and 27 °C. For `Candy Sunblaze', the rate of increase changed to a smaller slope beyond 25 °C. A piecewise linear regression change point model was fitted to each dataset. The base temperature (Tb) and the temperature at which the nonlinearity (Ti) occurred could then be determined. Tb for the phenophase BB:OF was 9.5 °C for `Candy Sunblaze' and 8.1 °C for `Red Sunblaze'. Ti for `Candy Sunblaze' was 24.9 °C for BB:VB and 25.6 °C for the phenophase BB:OF. The resulting point of change in rate of development prompted a modification of the traditional thermal unit formula. To complete the phenophase BB:OF using the modified formula, 479 degree days (°Cd) were predicted necessary for `Candy Sunblaze' and 589 °Cd for `Red Sunblaze'. Predicted time of events was compared with observed values. Subdividing BB:OF into BB:VB and VB:OF and using their respective Tb and thermal units summations (TU) reduced the average prediction error from 1.9 to 1.8 days for `Candy Sunblaze' and from 2.4 to 1.5 days for `Red Sunblaze'. In addition to single plant observations, phenological observations and thermal units were determined for pots with four plants to simulate commercial greenhouse crop production. Subdividing BB:OF into BB:VB and VB:OF and using their respective Tb and TU accumulations, reduced OF prediction errors on a crop basis for `Red Sunblaze', but was ineffective for `Candy Sunblaze'.

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P.R. Fisher, J.H. Lieth and R.D. Heins

Stem elongation of commercially produced flowering poinsettia (Euphorbia pulcherrima L.) is often sigmoid. However, sigmoid mathematical functions traditionally used for representing plant growth fail to adequately describe poinsettia stem elongation when a shoot has a long vegetative growth period. A model was developed that explicitly described three phases of poinsettia stem elongation: 1) the initial lag phase, where stem length increases approximately exponentially; 2) a period when elongation is linear; and 3) a plateau phase, where elongation rate declines to zero and stem length reaches an asymptotic maximum length. The timing of the plateau phase was linked to flower initiation date. Fit of the resulting model to data from single stem `Freedom' poinsettia grown with different periods between transplant and flower initiation had an R2 of 0.99. Model parameters had clear biological meaning, and the poinsettia model has horticultural application for simulation and graphical tracking of crop height.

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P.R. Fisher, J.H. Lieth and R.D. Heins

A model was developed to quantify the response of Easter lily (`Nellie White') flower bud elongation to average air temperature. Plants were grown in greenhouses set at 15, 18, 21, 24, or 27C after they had reached the visible bud stage. An exponential model fit the data with an R 2 of 0.996. The number of days until open flowering could be predicted using the model because buds consistently opened when they were 16 cm long. The model was validated against data sets of plants grown under constant and varying greenhouse temperatures at three locations, and it was more accurate and mathematically simpler than a previous bud elongation model. Bud length can be used by lily growers to predict the average temperature required to achieve a target flowering date, or the flowering date at a given average temperature. The model can be implemented in a computer decision-support system or in a tool termed a bud development meter.

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M. Raviv, J.H. Lieth and D.W. Burger

Rose plants (cv. Kardinal, grafted on Natal Brier) were grown in UC mix (42% fir bark, 33% peat, and 25% sand) and in coir. Water tension in the media was maintained within a predetermined narrow range using electronic tensiometers. Whole plant net photosynthesis as a function of the water tension in the medium was determined and the results were later normalized to measured leaf area. Simultaneous measurements of metabolic heat and respiration rate were carried out on detached young (FW = 10-20 mg.) leaflet samples, using differential scanning calorimeter (model 4100, Calorimetry Sciences, Provo, Utah). Only a small amount of plant material is removed for analyses so the assay is essentially non-destructive for the whole plant. Physical characteristics of the media greatly affect the relationship between water tension and water availability to plants. At similar tension values, water availability is much lower in coir than in UC mix. The effects of water availability on net photosynthesis, metabolic heat rate, and respiration will be discussed in relation to their effect on productivity.

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P.R. Fisher, J.H. Lieth and R.D. Heins

The objective was to predict the distribution (mean and variance) of flower opening for an Easter lily (Lilium longiflorum Thunb.) population based on the variability in an earlier phenological stage and the expected average temperature from that state until flowering. The thermal time from the visible bud stage until anthesis was calculated using published data. `Nellie White' grade 8/9 Easter lilies were grown in five research and commercial greenhouse locations during 1995, 1996, and 1997 under a variety of temperature and bulb-cooling regimes. Distributions of visible bud and anthesis were normally distributed for a population growing in a greenhouse with spatially homogenous temperatures. The variance at anthesis was positively correlated with variance at visible bud. The mean and variance at visible bud could therefore be used to predict the distribution of the occurrence of anthesis in the crop. The relationship between bud elongation, harvest, and temperature was also incorporated into the model. After visible bud, flower bud length measurements from a random sample of plants could be used to predict the harvest distribution. A computer decision-support system was developed to package the model for grower use.