J. Heinrich Lieth

A simulation model for the growth and development of flowering rose shoots

Abstract Mathematical models were selected or developed for the physiological processes involved in rose shoot growth and development. These were assembled into a model for simulating the response of rose shoot growth to photosynthetically active radiation and temperature. The patterns of simulated and observed shoot part dry weights were very similar. Dynamic patterns for processes such as leaf growth, assimilate production, import/export of assimilates and respiration were explored. Further work is needed on model refinement and validation.

SIGNIFICANCE OF SOILLESS CULTURE IN AGRICULTURE

This chapter explains soilless culture and describes its significance in agriculture. It begins with a historical account of facets of soilless culture in agriculture, suggesting that substrates used throughout the world differ significantly as to their make-up, while attempting to adhere to a specific set of principles. These principles are quite complex, relating to physical and chemical factors of solids, liquids, and gasses in the root zone of the plant. Today the largest industries in which soilless production dominates are greenhouse production of ornamentals and vegetables and outdoor container nursery production. In urban horticulture, virtually all containerized plants are grown without any field soil. Following this, it deals with hydroponics, which simply means, growing plants without soil. Initially scientists used hydroponics mainly as a research tool to study particular aspects of plant nutrition and root function. Progress in plastics manufacturing, automation, production of completely soluble fertilizers, and especially the development of many types of substrates complemented the scientific achievements and brought soilless cultivation to a viable commercial stage. Today various types of soilless systems exist for growing vegetables and ornamentals in greenhouses. This has resulted in a wide variety of growing systems. Finally, it presents an account of the current prevailing trends with respect to soilless media in agriculture, all over the world.

A decision-support system for real-time management of Easter lily (Lilium longiflorum Thunb.) scheduling and height—I. System description

Abstract A decision-support system was developed for recommending night and day temperature settings to control the timing and height of Easter lily ( Lilium longiflorum Thunb.). Existing biological models and qualitative rules were combined into an overall model of the response of plant development rate to temperature. A process control algorithm was used to determine appropriate height control actions based on a graphical control chart of plant height over time. A knowledge-based system checked the feasibility of output from the development and height control models and generated a text report. This model was implemented on a personal computer in a program called “The Greenhouse CARE System” and has been linked directly with an environmental computer to control greenhouse temperatures. A companion article describes validation of this model.

Effect of shoot-bending on productivity and economic value estimation of cut-flower roses grown in Coir and UC Mix

Shoot-bending, a common cultural practice in cut-flower rose production, results in a canopy consisting of horizontally bent shoots in addition to upright shoots. Production of this bent canopy was compared with hedgerow canopy for two rose cultivars, ‘Kardinal’ and ‘Fire N Ice’. In conjunction with the two canopy styles, two soil-less horticultural systems with different growing media (Coir versus UC Mix) were tested in a 2 × 2 factorial experiment. We investigated the number and length of all harvested flowering shoots as indicators of productivity and quality, respectively, from September 1997 to August 1999. While bent canopy produced longer stems and higher biomass of individual flowering shoots in both cultivars, this also resulted in significantly fewer harvestable flowering shoots. The comparison between Coir versus UC Mix was not as conclusive. ‘Fire N Ice’ plants grown in Coir produced more harvestable flowering shoots than plants grown in UC Mix, while ‘Kardinal’ did not. Neither cultivar showed differences in stem length and biomass production of the flowering shoots between Coir and UC Mix. Calculation of market value using a linearly increasing value index with stem length showed that with ‘Fire N Ice’ the improvement in stem length achieved by bent canopy did not offset the economic loss due to the reduction in the number of shoots per square meter. For ‘Kardinal’ the increased quality as a result of shoot-bending did offset the reduced production. In neither case did the combination of bent canopy and Coir generate significant improvements in value. Bent canopy became economically feasible when both short-stem discount and long-stem bonus were applied together. Published by Elsevier B.V.

Prediction of rose shoot development : model validation for the cultivar 'Cara Mia' and extension to the cultivars 'Royalty' and Sonia

Abstract Temperature effects on the rate of rose shoot development were previously modeled using a thermal units (heat units) approach (Pasian and Lieth, 1994). To validate that model, developmental events were tracked over time for ‘Cara Mia’, ‘Royalty’, and ‘Sonia’ rose ( Rosa hybrida ) plants. These events, consisting of the occurrence of ‘bud break’, unfolding of each leaf, ‘visible flower bud’, or ‘ready for harvest’ were recorded daily throughout the experiment period for shoots of each cultivar. Hourly average air temperatures were monitored continuously and used to compute the accumulated thermal units (benchmarks) to each developmental stage. The shoot development model developed previously was found to be valid for predicting the stages of development of ‘Cara Mia’ flowering shoots. This model, however, required adjustments for successful use with ‘Royalty’ and ‘Sonia’. Although the base temperatures used in the thermal units computation for ‘Royalty’ and ‘Sonia’ did not differ significantly from the one for ‘Cara Mia’, using cultivar-specific benchmarks resulted in significant prediction improvements. This indicates that benchmarks for each phenological stage need to be specific to each cultivar. The newly calculated benchmarks for the cultivars ‘Royalty’ and ‘Sonia’ require future validation. The model is suitable for timing of rose crops and deciding on temperature set-points.

Plant growth and development of Chrysanthemum and Ficus in aero-hydroponics: response to low dissolved oxygen concentrations

Abstract The growth of Chrysanthemum and Ficus plants in aero-hydroponics was reduced as the dissolved O2 concentration decreased; however, both species showed some adaptation to prolonged hypoxia in growth chamber experiments. Leaf number and plant height of Ficus plants grown in University of California (UC) mix or in water with an O2 concentration of 2 mg l−1 were lower than those in plants grown in O2-saturated water. Mathematical models were used to predict the time needed by Ficus plants growing in UC mix or aero-hydroponics to reach a particular leaf number. Ficus plants growing in O2-saturated water in aero-hydroponics produced leaves at the fastest rate.

Modeling stem elongation and leaf unfolding of Easter lily during greenhouse forcing

Abstract Equations were developed to predict stem elongation and leaf unfolding of potted Easter lily during the greenhouse forcing period. The average potting medium temperature was used in the stem elongation model to predict the day on which the stem emerged through the potting medium and the day when the first leaf unfolded. Together with an equation for the air temperature dependence of the leaf unfolding rate, these were built into a simulation model of the total number of Easter lily leaves unfolded during the greenhouse forcing period. This model predicts the data quite well, providing a tool for commercial monitoring of the development of this crop.

Irrigation in Soilless Production

Irrigation is the process of delivering water to plants so as to meet their needs for several important resources. There are several approaches to making irrigation decisions in the nursery: look-and-feel, gravimetric, timer-based, sensor-based, and model-based methods. While providing water is certainly a major facet of irrigation, various other nutrients, as well as oxygen, that are dissolved in the water are also provided to the plant at the same time. In soilless plant production, soluble fertilizers are frequently dissolved in the irrigation water using injection equipment. When the irrigation scheme includes soluble fertilizers dissolved in the irrigation water at various concentrations, this is called “fertigation.” Irrigation delivery systems are always designed to optimize various specific characteristics. This includes system capacity as well as system uniformity. The degree to which these characteristics are optimized has a greater impact on how irrigation is controlled rather than on the water utilization of the crop. All irrigation systems consist of tubing or pipe to transport the irrigation solution from the source to the individual plants or to a group of plants. Mixing or blending tanks assure that the dissolved materials are distributed uniformly within the water, and filters remove any insoluble materials. Irrigation schemes are management strategies developed to attain specific crop production goals utilizing various delivery and monitoring methods and refer to the overall plan of managing the irrigation water for the duration of the crop.

Variability in flower development of Easter lily (Lilium longiflorum Thunb.): model and decision-support system.

Abstract A model to predict the distribution of harvest dates in an Easter lily crop was validated using data from several locations. Plants were individually harvested (i.e. removed from the greenhouse for shipping) when flowers on a plant reached a minimum flower bud length. A computer decision-support system called LilyDate was developed to allow the model to be used to optimize greenhouse temperature settings to ensure that the majority of a crop is ready to harvest by a target date. To implement LilyDate, the user measures the length of the largest flower bud per plant on a sample of plants in the greenhouse, and enters the frequency of plants at each flower bud length (to the nearest cm) into the program. Based on the expected temperature and sample growth data, the software predicts a cumulative and daily distribution of when plants will be in flower. Model predictions were not biased, and the model predicted the number of days until 50 or 95% of plants were in flower with a precision of ±2 and ±3 days, respectively. The general approach to the computer system could be adapted to predict the harvest distribution for other crop species that require a consistent quantity of thermal time to harvest, and that are grown for a target harvest date.

Growing Plants in Soilless Culture: Operational Conclusions

This chapter presents the facets of soilless plant production, representing the state of the art and including some perspectives on the direction in which the field is moving, to provide practitioners with practical operational tools, allowing them to optimize crop production. It aims to develop a better understanding of the intricate processes taking place within the system along the root zone–plant–atmosphere continuum, as affected by the interactions among the growing substrate, the liquid and gaseous phases held in its matrix, and its nutritional status. The study verifies the concept presented by Mitcherlish, which suggests that plant productivity is limited by the nutritional factor that is limiting. This concept is appropriate if all factors except one are non-limiting. It also holds true in a broader sense when considering all factors that impact soilless crop production. However, when multiple factors are limiting, one must anticipate interacting effects which are more complex than simply suggesting causality of suboptimal production to the most-limiting factor. Finally, the study summarizes that horticultural engineering has significant opportunities in the area of integration of sensor technology with dynamic control over the root-zone variables that are the primary constraints to productivity.