Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Nitrogen uptake efficiency by white cedar under different irrigation and fertilisation strategies on a sandy soil: model calculations
    Pronk, A.A. ; Heinen, M. ; Heuvelink, E. ; Challa, H. - \ 2007
    Journal of Horticultural Science and Biotechnology 82 (2007)3. - ISSN 1462-0316 - p. 451 - 459.
    thuja-occidentalis brabant - dry mass-production - zero-sink uptake - ground cover - denitrification - mineralization - simulation - diffusion - nutrients - constant
    A combined conifer growth-soil water balance model was extended and parameterised to simulate the nitrogen (N) dynamics of a common nursery stock system [i.e., white cedar (Thuja occidentalis) grown for 2 years on a sandy soil]. The model was used to explore the effects on N uptake efficiency (Naue), N application rate (Nappl), and N loss (Nloss) of three irrigation strategies combined with a single, or a split fertiliser application at a recommended rate, without or with a correction for the mineral N content of the topsoil (Nmin,ts). Irrigation strategies used were: no irrigation, daily drip irrigation, or drip irrigation triggered by a pressure-head threshold value. Simulated N dynamics were in agreement with the measurements, but discrepancies were found between measured and simulated Nmin,ts. The simulated Naue was 29% in the first growing season, and 68% in the second growing season. Correcting for Nmin,ts reduced Nappl, especially in the non-irrigated strategy and in the threshold-irrigated strategy. Simulated Nloss during the 2-year growing period ranged from 79 kg N ha-1 for the non-irrigated strategy with a split-application, corrected for Nmin,ts, to 248 kg N ha-1 for the daily irrigated strategy with a split application. Simulated N concentrations in the percolating soil solution at a depth of 1 m exceeded the EU limit of 11.3 mg NO3-N l-1 in almost all simulations. In conclusion, additional measures are necessary to improve Naue, especially in the year of planting, to be able to reduce Nloss and meet the EU nitrate-N limit
    De integrale beplantingsmethode, naar een dynamische benadering voor het ontwerpen van beplantingen
    Ruyten, F. - \ 2006
    Wageningen University. Promotor(en): K. Kerkstra; H. Challa, co-promotor(en): Ron van Lammeren. - - 136
    landschapsarchitectuur - landschapsbouw - beplantingen - stadsparken - beplanten - selectiecriteria - planten - ontwerp - landscape architecture - landscaping - plantations - urban parks - planting - selection criteria - plants - design
    Public parks and gardens (planting structures) in urban areas are subject to various forms of human intervention, based on traditional planting methods. These forms of intervention are related to the creation of individual space required for mature growth of ligneous plants by thinning or by limiting growth in cases where plants exceed the space delineated for them. Such intervention is costly, must be executed timely in order to prevent irreversible deformity, and influences undamaged growth.

    The objective of this study is to resolve the contradiction between human intervention and undamaged growth by adopting a planting method which is based on a dynamic approach to the design of planting schemes. This dynamic approach has led to the integral planting method as a theoretical model; in this method, the space required for maximum growth in a plant's mature phase is combined with the realisation of architectural functions. The desired effect is defined by the initial size of the trees and shrubs. The growth movement towards the dimensions of the maturity phase is part of a composition in time and space in accordance with a so-called 'planting-film'. Because the growth rate of the plants defines the above-mentioned composition, human intervention can be reduced to a minimum. In addition, the integral planting method contains a set of instruments to define the space for growth to a certain size at a certain point in time in location-specific circumstances. By providing sufficient room for growth and by relating life span to environment dynamics, unexpected changes in future growth development can, to a certain extent, be compensated.

    The retrospective in Chapter 2 shows that with the planting method applied in the three cases (Haarzuilens, Amsterdamse Bos, Bijlmermeer Groenstructuur), people are always aiming for quick results and planning for future growth requires much effort, which must be enforced timely and systematically to ensure that the desired effect is not affected irreversibly (Bijlmermeer Park Structure) or operational backlog is not increased further.

    It is essential that the terminology used is unambiguous to define and legitimize the objective or intended development of a planting structure during the analysis phase. To achieve this unambiguousness, Chapter 3 provides a description of the morphology and morphodynamics (dimensions, growth rate, life span) of the elements used to describe the defined situation. This description, as defined in the tables 'Classification of free-standing forms', Planting typology I, II, III and IV, has led to unambiguous terms and definitions. This will lead to the motivation for the planting scheme (initial situation: initial dimensions, planting distances, assortment) and the planting film (the defined situation). Next, the 'growth', as the effect of movement, is derived from the growth curve survey for each element. The growth curve survey reproduces the morphodynamic aspects in a simplified linear growth curve. The transformations of planting types are shown tobe brought about on the basis of morphodynamics. The Cd-rom supplied with this thesis shows these dynamics from different angles, in the form of a planting film.

    Chapter 4 describes the principles of the adopted, not-adopted, identical and shifted position, with which the morphodynamic aspects of the plant can be applied strategically to also realise transformations of the plant types. The implementation of the growth curve survey shows how larger plant material can be used to start with. The example of a 2-acre park in Boxmeer shows what the principles for freestanding plant shapes bring about in real situations. The operating method and manual clarify how a starting situation (the planting scheme) and its related management regime (execution and maintenance plan) can be derived from the defined situation to which it should lead.

    In chapter 5 a comparison is made to ascertain how the integral planting method behaves in relation to the traditional method. When designing parks and gardens, the definition of assortment, planting interval, initial size and construction and maintenance method covers many variables such as architecture, micro climate, soil, opinions on contruction and maintenance method, quality of base materials, organisation of implementation and so on.These aspects are covered in anumber of cases (Polderpark Almere, Bakenhof Arnhem, Prins Bernhardbos Hoofddorp).

    The method applied in the comparison covers four steps. Step one describes the defined situation and the set-up according to the original planting method. Step two covers the growth curve survey which defines the location-specific morphodynamic characteristics of the plants involved for their actual as well as projected or future growth. Step three contains a fully worked-out planting and maintenance plan based on the alternative planting method and starting from the same defined situation as in step one.

    In step four the architectural and cost aspects of both planting methods are compared. The architectural aspects show the morphodynamics of the plant structure in the long term with the aid of views and diagrams drawn to scale, elucidated with data from the location-specific growth curve survey and field observations of the actual situation. The cost aspects are based on construction and maintenance for the first 30 years, expressed in cumulative, indexed and hard cash amounts, shown graphically for each planting method in the different cases.

    The results of the comparison show that a screen or block based on the traditional planting method will reach full functionality at eye level after 4 - 7 years. With the integral planting method, the results of a screen or block will be visible at eye level from the start, and full functionality will be reached after 8 - 13 years. With the traditional method, it appears to be almost impossible to realise free-standing forms, in practice as well as in simulation during the growth curve survey. Empirical research of the Prince Bernhard forest, which was developed according to the integral planting method, shows that the head start of the larger initial sizes of the free-standing forms in this method provides the visitor with an increased sense of security because of the openness of the plant structure and the fact that this method leads to a completed planting structure in a shorter period of time.

    In addition, the comparison shows that the construction costs using the integral planting method are about double the costs using the traditional planting method. However, the maintenance costs for free-standing forms when the integral planting method has been applied are so low, that cost recovery will occur within a foreseeable period, as compared with the traditional planting method (urban variant).

    The integral planting method can be applied to small- and large-scale urban and small-scale rural park projects. For large-scale rural projects application of the integral planting method requires further investigation of the relation between architectural functions of planting structures and forest ecology and forest management.

    Tree nurseries will need to put more effort into the methods for breeding and planting larger plant material. Some growers already guarantee that their plants will start growing immediately after planting and they offer care and maintenance of these larger inital sizes of trees and shrubs for a maintenance period of 10 years and longer.
    The Solar Greenhouse: state of the art in energy saving and sustainable energy supply
    Bot, G.P.A. ; Braak, N.J. van de; Challa, H. ; Hemming, S. ; Rieswijk, Th. ; Straten, G. van; Verlodt, I. - \ 2005
    Acta Horticulturae 691 (2005)2. - ISSN 0567-7572 - p. 501 - 508.
    The objective of the solar greenhouse project was the development of a Dutch greenhouse system for high value crop production without the use of fossil fuels. The project was completed and the results are reported here. The main approach was to first design a greenhouse system requiring much less energy, next to balance the availability of natural energy with the system¿s energy demand, and finally to design control algorithms for dynamic system control. This paper discusses the first two design steps. Increasing the insulation value of the greenhouse cover was the first step towards a reduction in energy demand. The challenge was in maintaining a high light transmission at the same time. A first generation of suitable materials was developed. The realizable energy saving is almost 40 %. The next reduction in fossil fuel requirement was accomplished by capturing solar energy from the greenhouse during the summer months, storing it in an underground aquifer at modest temperatures, and finally using the stored energy during the winter months by using heat pumps. Then the total realizable energy saving is more then 60%. For sustainable energy supply per ha greenhouse at this low energy demand 32 ha biomass is needed, or 600 kW nominal wind power or 1.2 ha PV assuming storage via the public grid.
    Dry mass production and water use of non- and drip irrigated Thuja occidentalis Brabant: field experiments and modeling
    Pronk, A.A. ; Heinen, M. ; Challa, H. - \ 2005
    Plant and Soil 268 (2005)1. - ISSN 0032-079X - p. 329 - 347.
    hydraulic conductivity - use efficiency - conifers - nitrogen - simulation - growth - roots - management - diffusion - stress
    Generally, irrigation increases dry mass production (DM) on sandy soils of horticultural crops and at the same time increases the risk of percolation losses of water and chemicals to below the root zone. However, the effects of irrigation are highly site-specific and not easily determined, which hampers the development of proper management tools and guidelines. A two-dimensional soil-water balance model combined with a crop growth model was parameterized and validated, and used to investigate DM and water use of Thuja occidentalis Brabant in a field trial under non- and drip irrigated conditions. Measured leaf DM and leaf area index (LAI) were not affected by irrigation but irrigation increased stem DM and the specific leaf area. Simulated DM and LAI were in good agreement with the measurements. Simulated pressure head followed the measured pressure head, although models performance was better under dry than under wet conditions. Simulation experiments indicated that increasing irrigation threshold levels increased DM production and leaching relatively to no irrigation, when the irrigation threshold level was measured at 0.25m depth
    The solar greenhouse: state of the art in energy saving and sustainable energy supply
    Bot, G.P.A. ; Braak, N.J. van de; Challa, H. ; Hemming-Hoffmann, S. ; Rieswijk, Th. ; Straten, G. van; Verlodt, I. - \ 2004
    In: Proceedings of GreenSys2004: Sustainable Greenhouse Systems, Leuven, Belgium, 12-16 september 2004. - - p. 132 - 132.
    The objective of the solar greenhouse project was the development of a Dutch greenhouse system for high value crop production without the use of fossil fuels. The project was completed and the results are reported here. The main approach was to first design a greenhouse system requiring much less energy, next to balance the availability of natural energy with the system's energy demand, and finally to design control algorithms for dynamic system control. This paper discusses the first two design steps. Increasing the insulation value of the greenhouse cover was the first step towards a reduction in energy demand. The challenge was in maintaining a high light transmission at the same time. A first generation of suitable materials was developed. The realizable energy saving is almost 40 %. The next reduction in fossil fuel requirement was accomplished by capturing solar energy from the greenhouse during the summer months, storing it in an underground aquifer at modest temperatures, and finally using the stored energy during the winter months by using heat pumps. Then the total realizable energy saving is more then 60%. For sustainable energy supply per ha greenhouse at this low energy demand 32 ha biomass is needed, or 600 kW nominal wind power or 1.2 ha PV assuming storage via the public grid.
    Temperature integration and process-based humidity control in chrysanthemum
    Körner, O. ; Challa, H. - \ 2004
    Computers and Electronics in Agriculture 43 (2004)1. - ISSN 0168-1699 - p. 1 - 22.
    grandiflorum ramat. kitamura - dendranthema x grandiflorum - greenhouse climate - air humidity - growth - morifolium - model - microclimate - irradiance - quality
    Simulations in the authors’ previous studies have shown that a modified temperature integration regime with a 6-day averaging period and increased set-point flexibility was able to reduce annual energy consumption by up to 9% as compared to a regular temperature integration regime. The commonly applied fixed set-point for relative humidity (RH) of 80–85% strongly reduced the potential for energy saving with this regime. Therefore, a more flexible humidity control regime was developed. Simulations indicated that yearly energy consumption could be reduced by 18% as compared to a fixed set-point of 80% RH. By combining the two regimes (temperature integration and humidity control), it was predicted that the energy saving would be even greater. To test this prediction, the combined regimes were applied in two experiments with cut-flower chrysanthemum crops investigating the effect on plant development and growth. Different temperature bandwidths for temperature integration (±2, ±4, ±6 and ±8 °C) were also compared within the joint regime. Crop development was only delayed with the ±8 °C temperature bandwidth. The best regime with respect to plant development, growth, quality and energy saving (±6 °C temperature bandwidth) was compared in a spring experiment with a climate regime used in commercial practice. Energy consumption was 23.5% less with the joint regime. No negative consequences of high humidity were observed, but there was a strong increase in the dry weight of all plant organs. Total plant dry weight was 39% higher than in the regular regime. It can be concluded that energy saving and crop yield increase can be achieved simultaneously, although the dynamic temperature control has to be adjusted to the chrysanthemum developmental stage. The combined dynamic climate regime forms a promising basis for future climate controllers and is easily extendable to other greenhouse crops.
    De Zonnekas : gewasproduktie zonder fossiele energie
    Bot, G.P.A. ; Verlodt, I. ; Hemming, S. ; Braak, N.J. van de; Challa, H. ; Straten, G. van; Riewijk, T. - \ 2003
    Wageningen : Wageningen Universiteit - 56
    glastuinbouw - zonne-energie - teeltsystemen - productie - bio-energie - energiebesparing - duurzaamheid (sustainability) - greenhouse horticulture - solar energy - cropping systems - production - bioenergy - energy saving - sustainability
    The Solar Greenhouse project aimed at the development of a greenhouse system for high value crop production with sustainable energy supply. The project meets the EET goal to substantially increase contribution of sustainable energy in energy supply. Moreover CO2 emission is reduced considerably. The research contained three themes: Decrease of the energy demand of the greenhouse system. Matching the time patterns of sustainable energy supply and greenhouse energy demand and Optimal control of the designed greenhouse system
    Process-based humidity control regime for greenhouse crops
    Korner, O. ; Challa, H. - \ 2003
    Computers and Electronics in Agriculture 39 (2003)3. - ISSN 0168-1699 - p. 173 - 192.
    glasshouse tomatoes - air humidity - growth - water - microclimate - quality - yield - model
    Modern greenhouses in The Netherlands are designed for efficient use of energy. Climate control traditionally aims at optimal crop performance. However, energy saving is a major issue for the development of new temperature regimes. Temperature integration (TI) results in fluctuating and often high relative humidity (RH) levels in modern, highly insulated greenhouses. At high temperature, water vapour pressure deficit (VPD) is usually high and RH consequently low and vice versa. Relatively low fixed set points (80¿85% RH) for air humidity as is common practice, may strongly influence the efficiency of TI, because heating and/or ventilation actions are required to control humidity rather than temperature. This requires much energy. Fluctuating RH may affect crop performance in several ways. Too low VPD may reduce growth due to low transpiration and associated physiological disorders. Water vapour pressure above the dew point leads to condensation on the relative cooler plant tissue and this may give rise to diseases. High VPD, on the other hand, may induce high stomatal resistance and plant water stress (PWS). The aim of the present research was the design of a process-based humidity control concept for a reference cut chrysanthemum crop cultivated with TI. RH control set points were generated as function of underlying processes. Greenhouse performance with this humidity regime and different temperature regimes were simulated with respect to greenhouse climate, energy consumption and photosynthesis. Compared with a fixed 80% RH set point, annual energy consumption of a year-round cut chrysanthemum cultivation could be reduced by 18% for TI with ±2 °C temperature bandwidth as well as for regular temperature control. For separate 12 week cultivations with planting date 1 March, energy saving could increase up to 27 or 23% for TI and regular temperature control, respectively.
    Using the expolinear growth equation for modelling crop growth in year-round cut chrysanthemum
    Lee, J.H. ; Goudriaan, J. ; Challa, H. - \ 2003
    Annals of Botany 92 (2003)5. - ISSN 0305-7364 - p. 697 - 708.
    oleracea l. botrytis - intercepted radiation - light interception - solar-radiation - use efficiency - young tomato - plant-growth - 3 densities - temperature - irradiance
    The aim of this study was to predict crop growth of year-round cut chrysanthemum (Chrysanthemum morifolium Ramat.) based on an empirical model of potential crop growth rate as a function of daily incident photosynthetically active radiation (PAR, MJ m¿2 d¿1), using generalized estimated parameters of the expolinear growth equation. For development of the model, chrysanthemum crops were grown in four experiments at different plant densities (32, 48, 64 and 80 plants m¿2), during different seasons (planting in January, May¿June and September) and under different light regimes [natural light, shading to 66 and 43 % of natural light, and supplementary assimilation light (ASS, 40¿48 µmol m¿2 s¿1)]. The expolinear growth equation as a function of time (EXPOT) or as a function of incident PAR integral (EXPOPAR) effectively described periodically measured total dry mass of shoot (R2 > 0·98). However, growth parameter estimates for the fitted EXPOPAR were more suitable as they were not correlated to each other. Coefficients of EXPOPAR characterized the relative growth rate per incident PAR integral [rm,i (MJ m¿2)¿1] and light use efficiency (LUE, g MJ¿1) at closed canopy. In all four experiments, no interaction effects between treatments on crop growth parameters were found. rm,i and LUE were not different between ASS and natural light treatments, but were increased significantly when light levels were reduced by shading in the summer experiments. There was no consistent effect of plant density on growth parameters. rm,i and LUE showed hyperbolic relationships to average daily incident PAR averaged over 10-d periods after planting (rm,i) or before final harvest (LUE). Based on those relationships, maximum relative growth rate (rm, g g¿1 d¿1) and maximum crop growth rate (cm, g m¿2 d¿1) were described successfully by rectangular hyperbolic relationships to daily incident PAR. In model validation, total dry mass of shoot (Wshoot, g m¿2) simulated over time was in good agreement with measured ones in three independent experiments, using daily incident PAR and leaf area index as inputs. Based on these results, it is concluded that the expolinear growth equation is a useful tool for quantifying cut chrysanthemum growth parameters and comparing growth parameter values between different treatments, especially when light is the growth-limiting factor. Under controlled environmental conditions the regression model worked satisfactorily, hence the model may be applied as a simple tool for understanding crop growth behaviour under seasonal variation in daily light integral, and for planning cropping systems of year-round cut chrysanthemum. However, further research on leaf area development in cut chrysanthemum is required to advance chrysanthemum crop growth prediction
    Temperature integration and DIF in cut chrysanthemum
    Korner, O. ; Challa, H. - \ 2003
    Journal of Horticultural Science and Biotechnology 78 (2003)3. - ISSN 1462-0316 - p. 335 - 342.
    To reduce energy consumption in greenhouses, temperature integration can be used. However, the temperature integration principle considers only average temperatures and does not comply with the DIF concept (difference between mean day temperature and mean night temperature). With DIF, stem elongation, one of the major quality aspects of many crops, can be controlled. Short compact plants can be achieved by a negative DIF (average night temperature > average day temperature). In spring, summer and autumn temperature integration usually results in positive DIF and therefore longer stems. The aim of this study was to investigate whether temperature integration and DIF could be applied simultaneously. Greenhouse temperature fluctuates with temperature integration. During spring or autumn it is difficult to obtain short compact plants by a negative DIF with regular temperature integration. In this research, temperature integration was therefore modified by applying two independent integration regimes, one for daytime and one for nighttime while a zero DIF was set. Simulations and experiments with standard temperature control, regular and modified temperature integration showed that temperature integration and DIF could be applied simultaneously, while energy consumption and stem elongation were reduced
    Dry mass production and leaf area development of field-grown ornamental conifers: measurements and simulation
    Pronk, A.A. ; Heuvelink, E. ; Challa, H. - \ 2003
    Agricultural Systems 78 (2003)3. - ISSN 0308-521X - p. 337 - 353.
    radiation interception - use efficiency - model - forest - index - photosynthesis - lai-2000 - density - trees
    A dynamic simulation model of dry mass (DM) production and leaf area index (LAI) development in ornamental conifers, CONGRO, was developed. The concept of a constant radiation use efficiency (RUE) was combined with a model for radiation interception by row crops. A field trial was used to calibrate RUE, DM partitioning and the specific leaf area (SLA). LAI increase was simulated through leaf dry mass increase and SLA. Ten independent trials (1991–1999) were used for validation. Predicted aboveground DM agreed well with measured data (R2=0.94) with a standard error of the regression of 149 g m-2. Predicted LAI agreed less with experimental field data (R2=0.90), standard error of the regression was 0.312 m2 m-2. Sensitivity analysis showed a large positive sometimes more than proportional effect of RUE, SLA and partitioning into the leaf dry mass on simulated total DM, LDM, LAI and intercepted radiation.
    A simple method to estimate radiation interception by nursery stock conifers: a case study of eastern white cedar
    Pronk, A.A. ; Goudriaan, J. ; Stilma, E.S.C. ; Challa, H. - \ 2003
    NJAS Wageningen Journal of Life Sciences 51 (2003)3. - ISSN 1573-5214 - p. 279 - 295.
    thuja occidentalis - plantmateriaal - kroondak - interceptie - zonnestraling - schatting - thuja occidentalis - planting stock - canopy - interception - solar radiation - estimation - leaf-area index - lai-2000 - photosynthesis - canopies - stands - model
    A simple method was developed to estimate the fraction radiation intercepted by small eastern white cedar plants (Thuja occidentalis 'Brabant'). The method, which describes the crop canopy as rows of cuboids, was compared with methods used for estimating radiation interception by crops with homogeneous canopies and crops grown in rows. The extinction coefficient k was determined at different plant arrangements and an average k-value of 0.48 ± 0.03 (R2 = 0.89) was used in the calculations. Effects of changing plant characteristics and inter- and intra-row plant distances were explored. The fraction radiation intercepted that was estimated with the method for rows of cuboids was up to 20% and for row crops up to 8% lower than estimated with the method for homogeneous canopies at low plant densities and a LAI of 1. The fraction radiation intercepted by small plants of Thuja occidentals 'Brabant' was best estimated by the simple method described in this paper
    Crop based climate regimes for energy saving in greenhouse cultivation
    Körner, O. - \ 2003
    Wageningen University. Promotor(en): H. Challa. - [S.l.] : S.n. - ISBN 9789058088611 - 240
    chrysanten - kasgewassen - kassen - teelt onder bescherming - gecontroleerde omgeving - duurzaamheid (sustainability) - fotosynthese - simulatiemodellen - energiebesparing - chrysanthemums - greenhouse crops - greenhouses - protected cultivation - controlled atmospheres - sustainability - photosynthesis - simulation models - energy saving

    Key words: Biocides, cut chrysanthemum, Chrysanthemum grandiflorum , CO 2 , crop photosynthesis, DIF , energy saving, fungal diseases, humidity control, plant quality, simulation model, stem elongation, temperature integration.

    Sustainability is one of the major aims in greenhouse horticulture. According to agreements between the Dutch grower association and the government, energy consumption and the use of chemical biocides have to be reduced. More advanced greenhouse technique is being developed to reach the target to decrease the energy efficiency-index by 65 % between 1980 and 2010. However, this could also be achieved with existing technology by using more advanced climate regimes. The present thesis aimed at that, through designing and analysing climate regimes while employing existing climate control possibilities. Theoretical temperature and humidity regimes were designed to decrease energy consumption and a photosynthesis maximisation procedure was implemented to maximise growth.

    The basis for a crop gross photosynthesis model for control purposes was created. Crop photosynthesis models were evaluated at conditions expected to occur with more sustainable climate regimes. It was shown with experimental evidence that theoretical assumptions on the temperature - CO 2 effects in a crop that are based on theoretically models scaling up leaf photosynthesis to the crop level are valid and that simplified existing models could be applied up to 28°C. With higher temperatures new designs are needed and this can probably be achieved with an improved stomata-resistance model.

    The well known temperature integration principle was modified with two nested time-frames (24-hour and six days) and a temperature dose-response function. In a year round tomato cultivation, energy consumption was predicted to decrease with up to 9 % compared to regular temperature integration.

    The potential for energy saving with temperature integration is limited by humidity control when as usual fixed set points are maintained, because it counteracts temperature integration. Vents open at lower temperatures and heating is switched on at higher temperatures than required for optimal effects of temperature integration. A new approach to control relative humidity on the underlying processes (crop growth and development, plant water stress, calcium deficiencies and the major fungal diseases) by controlling relative humidity through maximum leaf wetness duration, minimum transpiration and transpiration integral was designed for cut chrysanthemum. This idea is based on earlier formulations to use set points for transpiration. In the current approach, general rules were formulated. From that, a control regime was designed. Simulations showed that with this humidity regime, yearly energy consumption could be reduced by 18 % (compared to a fixed setpoint of 80 % relative humidity).

    When the two climate control principles, modified temperature integration and process based humidity control, were merged, annual energy consumption was predicted to decrease by more than 33 % and cut chrysanthemum plant dry weight increased with 39 % in experiments compared to a normal climate regime.

    Cut chrysanthemum was used as a central crop. Here, short compact stems is one of the main quality aspects. This is commonly controlled with chemical growth retardants. An alternative is to control temperature according to the DIF concept (difference between average day and average night temperature). A negative DIF value decreases stem elongation. Therefore, temperature integration without DIF restriction was extensively compared to temperature integration with DIF restriction. Energy consumption with different settings was quantified. It was shown that an optimisation problem existed in spring and summer. For that purpose, a joined temperature integration and DIF regime over several days was designed and tested. The use of an average DIF over several days rather than a DIF within 24-hours was proposed. In times and climate regions when cold and warm days interchange, this approach can increase energy saving and decrease final plant stem length simultaneously. This however, was a compromise. An optimisation problem between the two regimes aiming at sustainable greenhouse horticulture remained (less energy consumption versus reduction in application of biocides). This can only be solved when detailed models for crop quality, development and growth will become available.

    The regimes could be applied in commercial greenhouses with only little adjustment. The only additional expense is a computer functioning as set point generator, and a suitable interface with the existing climate computer. In addition, the achieved degrees of freedom for two main states (temperature and humidity) form a promising perspective for future optimal greenhouse climate control. The regimes, however, were based on many arbitrary assumptions. More research is needed for parameterisation.

    Design for an improved temperature intregration concept in greenhouse cultivation
    Körner, O. ; Challa, H. - \ 2003
    Computers and Electronics in Agriculture 39 (2003)1. - ISSN 0168-1699 - p. 39 - 59.
    plants - tomato - leaves
    The ability of crops to tolerate temperature deviations from the average set point could play an important role in energy saving greenhouse climate regimes. This principle is used in the so called temperature integration procedure, which is based on empirical knowledge and uses fixed maximum and minimum temperatures. More dynamic flexible boundaries depending on the underlying crop processes would probably increase the potential for energy saving in greenhouses. Therefore, our aim was to improve the temperature integration concept by introducing dynamic temperature constraints. Processes with a fast temperature response (e.g. photosynthesis or stress) were decoupled from developmental processes with a slow response time. A,modified temperature integration procedure was designed combining the usual long-term integration over several days and fixed boundaries for daily average temperature with short-term integration over 24 h with flexible temperature limits. Because the optimum temperature for canopy photosynthesis rises with increasing concentration of atmospheric CO2, this aspect was included in ventilation control. Because plants react not only to extreme temperatures but also to their duration, a dose concept was applied to stress-related temperature constraints: The desired mean temperature for the subsequent 24 h was calculated once in 24 h. Within this 24 h cycle, temperature set points for heating and ventilation were optimised in relation to the fast crop processes. The temperature regime was tested by simulations. Greenhouse climate, energy consumption and dry matter increase were simulated for complete: years and different parameter settings for tomato as model crop. With the modified regime compared with regular temperature integration, with the same +/-2 degreesC long-term temperature bandwidth 4.5% (normal secure settings) or up to 9% (extreme settings) more energy could be saved (on a yearly basis). Crop gross photosynthesis could increase by approximately 2.5%. (C) 2003 Elsevier Science B.V. All rights reserved.
    Modelling temperature effects on crop photosynthesis at high radiation in a solar greenhouse
    Körner, O. ; Challa, H. ; Ooteghem, R.J.C. van - \ 2003
    Acta Horticulturae (2003)593. - ISSN 0567-7572 - p. 137 - 144.
    Development of fine and coarse roots of Thuja occidentalis 'Brabant' in non-irrigated and drip irrigated field plots
    Pronk, A.A. ; Willigen, P. de; Heuvelink, E. ; Challa, H. - \ 2002
    Plant and Soil 243 (2002)2. - ISSN 0032-079X - p. 161 - 171.
    douglas-fir stands - sandy soils - growth - density - netherlands - biomass - model
    Aboveground dry mass, total root dry mass and root length density of the fine roots of Thuja occidentalis `Brabant' were determined under non- and drip-irrigated field conditions. Two-dimensional diffusion parameters for dynamic root growth were estimated based on dry mass production of the fine roots and the concept of the convective-diffusion model of cylindrical root growth and proliferation. Drip irrigation increased above-ground dry mass and the shoot:root ratio compared with no irrigation. Dry mass of the coarse roots increased as well due to drip irrigation. No effect on total or fine root dry mass was found. Drip irrigation increased root length densities in the top 0.1 m but not significantly. However, drip irrigation decreased root proliferation in depth by 27%, whereas proliferation in the horizontal direction was not altered. Measured root length densities were overestimated by 6-21% by the model (0.68
    A simulation study on the interactive effects of radiation and plant density on growth of cut chrysanthemum
    Lee, J.H. ; Heuvelink, E. ; Challa, H. - \ 2002
    Acta Horticulturae 593 (2002). - ISSN 0567-7572 - p. 151 - 157.
    In the present study, we used a photosynthesis-driven crop growth model to determine acceptable plant densities for cut chrysanthemum throughout the year at different intensities of supplementary light. Dry matter partitioning between leaves, stems, and flowers was simulated as a function of crop developmental stage. Leaf area index was simulated as leaf dry mass multiplied by specific leaf area, the latter being a function of season. Climatic data (hourly global radiation, greenhouse temperature, and CO2 concentration) and initial organ dry mass were model inputs. Assimilation lights were switched on and off based on time and ambient global radiation intensity. Simulated plant fresh mass with supplementary light (49 µmol m-2 s-1) for 52 cultivations (weekly plantings, reference plant densities, and length of the long and short day period) was used as reference plant fresh mass. For four other supplementary light intensities (31, 67, 85, and 104 µmol m-2 s-1), dry matter production was simulated with the reference plant density and length of the long and short day period for each planting week and plant fresh mass was calculated. The acceptable plant density was then calculated as the ratio between plant fresh mass and reference plant fresh mass multiplied by the reference density. Under low natural light intensities, plant density could be increased substantially (>30%) at increased supplementary light intensities, while maintaining the desired plant mass. Simulated light use efficiency (g additional dry mass ¿ MJ-1 additional supplementary light) was higher in winter (4.7) than in summer (3.5), whereas it hardly differed between the supplementary light intensities. This type of simulations can be used to support decisions on the acceptable level of plant density at different intensities of supplementary lighting or lighting strategies and on optimum supplementary light intensities.
    Crop models for greenhouse production systems
    Challa, H. - \ 2002
    Acta Horticulturae 593 (2002). - ISSN 0567-7572 - p. 47 - 53.
    Crop quality control system: a tool to control the visual quality of pot plants
    Dijkshoorn-Dekker, M.W.C. - \ 2002
    Wageningen University. Promotor(en): H. Challa. - S.l. : S.n. - ISBN 9789058087010 - 117
    gewaskwaliteit - kwaliteitscontroles - modellen - beeldverwerking - neurale netwerken - potplanten - ficus benjamina - bedrijfsinformatiesystemen - crop quality - quality controls - models - image processing - neural networks - pot plants - ficus benjamina - management information systems

    Key words: quality, growth, model, leaf unfolding rate, internode, plant height, plant width, leaf area, temperature, plant spacing, season, light, development, image processing, grading, neural network, pot plant, Ficus benjamina 'Exotica'.

    The market is increasingly dictating the specifications for products. A well-defined marketable product must be delivered at a defined moment in time. A system was developed for growers to control development and growth of pot plants to achieve a defined quality on a specified delivery date.

    A theoretical framework of quality modelling used in the food industry was successfully implemented within the domain of pot plants. The visual quality of Ficus benjamina 'Exotica' was explained for 88.7% by four variables (in addition to the fixed plant height of 1.20 m.): the density of the leaf mass in front-view, 40-60 cm above pot rim; the width in side view, 40-60 cm above pot rim; the width in front-view, 0-20 and 20-40 cm above pot rim. Effect of temperature, plant density (control factors) and season (not controlled) on the growth and development of Ficus in relation to these quality features was quantified. Development of Ficus benjamina 'Exotica' showed a regular pattern. Plant height increased with temperature up to 29.5°C. The effect of plant density on this variable was small. Leaf unfolding rate was influenced by light and temperature, plant density was of minor influence. Its response to temperature showed an optimum at 30°C. The final internode length was mainly affected by light intensity, temperature had no effect. The width of the plant and the density of leaf mass increased at lower plant densities. The effect of temperature on visual quality of Ficus was small. A simple model based on only two major quality features, plant height and plant width, was developed and could successfully control visual quality of Ficus . Plant height as a function of plastochron age and internode length in relation to temperature and light was adequately predicted. Plant width was successfully controlled by spacing operations, using image processing to monitor this crop feature.

    By integration of four functional modules, a model for visual quality, a crop growth control model, image processing to monitor crop development and a neural network to grade plants, a crop quality control system (CQCS) was obtained and successfully implemented. This system was compared to other systems and its limitations and transferability to other crops was discussed. Furthermore, the system was evaluated for commercial practice.

    The role of the leaf on the dynamics of growth and rooting of leafy stem cuttings of rose
    Cunha Costa, J.M.R. da - \ 2002
    Wageningen University. Promotor(en): H. Challa; M.T.M. Willemse; U. van Meeteren; P.A. van de Pol; C.J. Keijzer. - S.l. : S.n. - ISBN 9789058086877 - 187
    rosaceae - rozen - stekken - bladeren - wortels - beworteling - stengels - fotosynthese - groei - plantengroeiregulatoren - bladoppervlakte - plantenvermeerdering - voedingsstoffenreserves - rosaceae - roses - cuttings - leaves - leaf area - roots - rooting - stems - photosynthesis - growth - plant growth regulators - propagation - nutrient reserves

    Key words : Rosa hybrida , cut-rose, propagation, cuttings, leaf, rooting, root initiation, root growth, axillary primary shoot, severance, photosynthesis, carbohydrates, reduced sink activity, planting material, quality

    The present study aims at better understanding the relation between photosynthesis of the original leaf, carbohydrates, rooting and growth of single node leafy stem cuttings of rose. This knowledge can be used to improve success and efficiency in propagation and improving the uniformity of the planting material of cut roses derived form cuttings.

    The effects of the original leaf area on the growth of cuttings of Rosa hybrida Madelon ®were investigated during the first 10 weeks after severance. Total plant dry weight, and dry weight of the roots in particular, were proportionally related with the original leaf area of cuttings. When leaf area was modified, leaf area duration was linearly related to the rooting and growth of cuttings during the first 21 days of propagation. The presence of the leaf during the first week of propagation was critical for survival and its removal caused stem rot. This was caused by low carbohydrate concentrations.

    Cuttings remained photosyntheticaly active after severance. Photosynthetic rates decreased immediately after severance, but recovered up to 70% of the rates measured on leaves on mother plants and remained constant during propagation. The PSII efficiency decreased during propagation with a simultaneous increase in its heterogeneity across the leaflets (patchiness) which may be attributed to decreased sink activity rather then to water stress. The root and shoot tissues accounted for about 70% of the increase in total fresh weight after 21 days of propagation, whereas the remaining 30% increase was due to dry weight accumulation in the leaf and stem. About 55% of the dry weight accumulated consisted of carbohydrates, in particular starch, which accumulated mainly in the first 14 days in leaves and stem tissues (pith and medullar rays). This accumulation may be explained by reduced meristematic sink activity following severance. In fact, the newly formed roots and primary shoot after 21 days of propagation only represented 10% of the total dry weight of cuttings.

    Reduced light integrals and low CO 2 concentrations resulted in reduced rooting and growth of cuttings and decreased carbohydrate levels. Number of roots, and particularly, dry weight of roots, were linearly related with total dry weight accumulation during the 21 days of propagation showing that photosynthetic activity of cuttings during propagation influences both root initiation and growth. The effects of low light, low CO 2 concentration, and leaf area reduction on rooting and growth of cuttings were similar indicating that these effects could be explained to a great extent by photosynthesis. Growth in general depended on the length of the period cuttings were photosynthetically active during propagation. An exception was the growth of the axillary primary shoot, which was more negatively affected by reduced photosynthetic activity in the first 11 days of propagation. Root initiation was also more negatively affected by low photosynthetic activity in the first 11 days of propagation whereas root growth responded to the integral of photosynthesis. Cuttings were able to efficiently use reserves for growth. Optimal rooting and further growth of cuttings rely on the synthesis of new photosynthates because storage is limited in single node stem cuttings.

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