Search

Funded by Kas als Energiebron, Wageningen UR Greenhouse Horticulture conducted an experiment witth cucumber in the Venlow Energy greenhouse with a high-wire system. The objective was to achieve a minimal evaporation during cultivation under double glazing and a film screen. In the night the evaporation fell to 15-25 g. m-2.hour-1. This was enough to grow cucumbers without deficiency symptoms. Only in March, some degree of “bolblad” occurred, but after a few sunny days the crop well recovered. The film screen was kept closed until 2 hours after sunset and one hour before sundown closed. This provided no problems for cultivation. In the night the humidity could rise above 95% without Mycosphearella problems. For the new cultivation strategy this means if other factors such as horizontal uniformity of the climate are good that cultivation in high humidity and with minimal ventilation is possible. For the Venlow Energy greenhouse ventilation rate was 0.37 and this delivers in winter conditions a sufficient degree of natural ventilation and moisture management. ReferaatIn opdracht van Kas als Energiebron heeft Wageningen UR Glastuinbouw in de Venlow Energy kas een hogedraad teelt komkommer uitgevoerd. Doelstelling was een minimale verdamping te realiseren bij teelt onderdubbel glas en een folie scherm. In de nacht daalde de verdamping tot 15-25 g.m-2.uur-1. Dit was voldoende omzonder gebreks verschijnselen de komkommers te telen. Alleen in maart kwam enige mate van bolblad voor,maar na een paar zonnige dagen herstelde het gewas zich goed.Het foliescherm is tot 2 uur na zon-op gesloten gehouden en 1 uur voor zon-onder weer gesloten. Dit leverdevoor de groei geen problemen op. In de nacht kon de luchtvochtigheid oplopen tot boven de 95% zonder dat erMycosphearella is ontstaan.Voor het nieuwe telen betekent dit dat als de overige factoren zoals horizontale uniformiteit van het klimaat goedzijn dat bij hoge luchtvochtigheid en met minimale vochtafvoer kan worden geteeld. Voor de Venlow Energy kaswas het ventilatievoud 0.37 en dat levert in winter condities een voldoende mate van natuurlijke ventilatie envochtafvoer op.AbstractFunded by Kas als Energiebron, Wageningen UR Greenhouse Horticulture conducted an experiment witthcucumber in the Venlow Energy greenhouse with a high-wire system. The objective was to achieve a minimalevaporation during cultivation under double glazing and a film screen. In the night the evaporation fell to 15-25g. m-2.hour-1. This was enough to grow cucumbers without deficiency symptoms. Only in March, some degree of“bolblad” occurred, but after a few sunny days the crop well recovered.The film screen was kept closed until 2 hours after sunset and one hour before sundown closed. This provided noproblems for cultivation. In the night the humidity could rise above 95% without Mycosphearella problems.For the new cultivation strategy this means if other factors such as horizontal uniformity of the climate are goodthat cultivation in high humidity and with minimal ventilation is possible. For the Venlow Energy greenhouseventilation rate was 0.37 and this delivers in winter conditions a sufficient degree of natural ventilation andmoisture management.

Varens wijken in veel opzichten af van andere potplanten. Ze vormen geen bloemen en de voortplanting is een ingewikkelde zaak. Ook inwendig kennen ze tal van bijzonderheden. Daarom is het des te verwonderlijker dat ze op de bedrijven gewoon tussen andere groene planten kunnen worden geteeld.

Irradiance is the main driver of photosynthesis. In natural conditions, irradiance incident on a leaf often fluctuates, due to the movement of leaves, clouds and the sun. These fluctuations force photosynthesis to respond dynamically, however with delays that are subject to rate constants of underlying processes, such as regulation of electron transport, activation states of enzymes in the Calvin cycle, and stomatal conductance (gs). For example, in leaves adapted to low irradiance that are suddenly exposed to high irradiance, photosynthesis increases slowly (within tens of minutes); this process is called photosynthetic induction. Photosynthesis in fluctuating irradiance (dynamic photosynthesis) is limited by several physiological processes, and is further modulated by environmental factors other than irradiance, such as CO2 concentration, air humidity and temperature. Studying dynamic photosynthesis and its environmental and physiological control can help to identify targets for improvements of crop growth, improve the accuracy of mathematical models of photosynthesis, and explore new, dynamic lighting strategies in greenhouses. In this thesis, the limitations acting on dynamic photosynthesis are explored by reviewing the literature, by experimenting with a suite of environmental factors (CO2 concentration, temperature, air humidity, irradiance intensity and spectrum), genetic diversity in the form of mutants, genetic transformants and ecotypes, and by mathematical modelling. Several genotypes of tomato (Solanum lycopersicum) and the model plant Arabidopsis thaliana, all grown in climate chambers, were used in the experiments. The main findings of the thesis are that a) CO2 concentration and air humidity strongly affect the rate of change of dynamic photosynthesis through a combination of diffusional and biochemical limitations; b) Rubisco activation kinetics are pivotal in controlling rates of photosynthesis increase after a stepwise increase in irradiance, and are further affected by CO2 concentration; c) gs limits photosynthetic induction kinetics in A. thaliana but not in tomato in ambient conditions, and becomes a stronger limitation in low CO2 concentration or air humidity; and d) mesophyll conductance, non-photochemical quenching (NPQ) and sucrose synthesis do not limit dynamic photosynthesis under the conditions used. In Chapter 1, the rationale for the research conducted is described, by introducing the concept of fluctuating irradiance and its effects on photosynthesis rates. The chapter discusses how dynamic photosynthesis is measured and described, and provides a range of possible applications of the insights gained by the research conducted in this dissertation. In Chapter 2, the current literature is reviewed and a mechanistic framework is built to explore the effects that the environmental factors CO2 concentration, temperature and air humidity have on rates of dynamic photosynthesis. Across data from literature, higher CO2 concentration and temperature speed up photosynthetic induction and slow down its loss, thereby facilitating higher rates of dynamic photosynthesis. Major knowledge gaps exist regarding the loss of photosynthetic induction in low irradiance, dynamic changes in mesophyll conductance, and the extent of limitations imposed by gs across species and environmental conditions. Chapter 3 is an experimental exploration of the effects of CO2 concentration, leaf temperature, air humidity and percentage of blue irradiance on rates of photosynthetic induction in dark-adapted tomato leaves. Rubisco activation, changes in stomatal and mesophyll conductance, diffusional and biochemical limitations, efficiency of electron transport through photosystem II, NPQ and transient water use efficiency, were examined to give a comprehensive overview of the environmental modulation of dynamic photosynthesis. Unlike the percentage of blue irradiance, increases in CO2 concentration, leaf temperature and air humidity all positively affected the rates of photosynthetic induction, and these effects were explained by changes in diffusional and biochemical limitations. Maximising the rates of Rubisco activation would increase CO2 assimilation by 6-10%, while maximising the rates of stomatal opening would increase assimilation by at most 1-2%, at the same time negatively affecting intrinsic water use efficiency. In Chapter 4 it is explored whether the effects of CO2 concentration on dynamic photosynthesis are similar across various irradiance environments. Gain and loss of photosynthetic induction in several low irradiance treatments, as well as sinusoidal changes in irradiance, were studied using tomato leaves. Elevated CO2 concentration (800 ppm) enhanced the rate of photosynthetic induction by 4-12% (compared to 400 ppm) and decreased the loss of photosynthetic induction by 21-25%. Elevated CO2 concentration enhanced rates of dynamic photosynthesis regardless of initial photosynthetic induction state to a similar extent. Therefore, rising global CO2 concentration will benefit integrated assimilation throughout whole canopies, where different leaf layers experience widely differing irradiance regimes. In Chapter 5 it is tested whether stomatal limitation exists during photosynthetic induction in tomato leaves. The abscisic acid-deficient flacca mutant and its wildtype were exposed to various CO2 concentrations to change the diffusion gradient. Despite gs being much larger in flacca, photosynthetic induction proceeded with the same speed in both genotypes in ambient CO2 concentration. This suggested that stomata did not limit photosynthetic induction in the wildtype. Using these findings, several indices of stomatal limitations were compared. Diffusional limitation, a new index, was found to be the most useful. In Chapter 6, an exploration of some physiological limitations underlying dynamic photosynthesis is undertaken. Several mutants, transformants and ecotypes of A. thaliana, affecting rates of Rubisco activation, gs, NPQ and sucrose metabolism, were used. Next to a characterisation of their steady-state responses to CO2 concentrations and irradiance, leaves were exposed to stepwise increases and decreases in irradiance (using several intensities) and to lightflecks of several amplitudes and frequencies. Rubisco activase isoform and concentration, as well as various levels of gs, strongly affected rates of dynamic photosynthesis, while this was not the case with low NPQ or sucrose phosphate synthase concentration. This suggests Rubisco activase and gs as targets for improvement of photosynthesis in fluctuating irradiance. Chapter 7 is a modelling exercise of dynamic photosynthesis, based on data obtained from measurements on mutants of A. thaliana (Chapter 6). This includes a goal-seeking model that allows reproducing the regulation of Rubisco by irradiance and CO2 concentration. The model also includes a full description of leaf-level NPQ, incorporates mesophyll conductance and accounts for the fundamental physics of delays introduced by open gas exchange systems on CO2 measurements. Different data sets for model calibration and validation were used. It was found that the model accurately predicted the effects of the mutants, suggesting that the assumptions of the model were sound and represented the underlying mechanisms correctly. In Chapter 8, the findings in this thesis are synthesized. The insights gained throughout this dissertation are related to existing literature to give a comprehensive overview of the state of knowledge about the limitations of dynamic photosynthesis. The methodology of assessing transient stomatal limitations, and some aspects of using chlorophyll fluorescence measurements during photosynthetic induction, are discussed. Finally, possible applications and ideas for future research on photosynthesis in fluctuating irradiance are discussed.

Funded by Kas als Energiebron, Wageningen UR Greenhouse Horticulture conducted an experiment witth cucumber in the Venlow Energy greenhouse with a high-wire system. The objective was to achieve a minimal evaporation during cultivation under double glazing and a film screen. In the night the evaporation fell to 15-25 g. m-2.hour-1. This was enough to grow cucumbers without deficiency symptoms. Only in March, some degree of “bolblad” occurred, but after a few sunny days the crop well recovered. The film screen was kept closed until 2 hours after sunset and one hour before sundown closed. This provided no problems for cultivation. In the night the humidity could rise above 95% without Mycosphearella problems. For the new cultivation strategy this means if other factors such as horizontal uniformity of the climate are good that cultivation in high humidity and with minimal ventilation is possible. For the Venlow Energy greenhouse ventilation rate was 0.37 and this delivers in winter conditions a sufficient degree of natural ventilation and moisture management.

Irradiance is the main driver of photosynthesis. In natural conditions, irradiance incident on a leaf often fluctuates, due to the movement of leaves, clouds and the sun. These fluctuations force photosynthesis to respond dynamically, however with delays that are subject to rate constants of underlying processes, such as regulation of electron transport, activation states of enzymes in the Calvin cycle, and stomatal conductance (gs). For example, in leaves adapted to low irradiance that are suddenly exposed to high irradiance, photosynthesis increases slowly (within tens of minutes); this process is called photosynthetic induction. Photosynthesis in fluctuating irradiance (dynamic photosynthesis) is limited by several physiological processes, and is further modulated by environmental factors other than irradiance, such as CO2 concentration, air humidity and temperature. Studying dynamic photosynthesis and its environmental and physiological control can help to identify targets for improvements of crop growth, improve the accuracy of mathematical models of photosynthesis, and explore new, dynamic lighting strategies in greenhouses. In this thesis, the limitations acting on dynamic photosynthesis are explored by reviewing the literature, by experimenting with a suite of environmental factors (CO2 concentration, temperature, air humidity, irradiance intensity and spectrum), genetic diversity in the form of mutants, genetic transformants and ecotypes, and by mathematical modelling. Several genotypes of tomato (Solanum lycopersicum) and the model plant Arabidopsis thaliana, all grown in climate chambers, were used in the experiments. The main findings of the thesis are that a) CO2 concentration and air humidity strongly affect the rate of change of dynamic photosynthesis through a combination of diffusional and biochemical limitations; b) Rubisco activation kinetics are pivotal in controlling rates of photosynthesis increase after a stepwise increase in irradiance, and are further affected by CO2 concentration; c) gs limits photosynthetic induction kinetics in A. thaliana but not in tomato in ambient conditions, and becomes a stronger limitation in low CO2 concentration or air humidity; and d) mesophyll conductance, non-photochemical quenching (NPQ) and sucrose synthesis do not limit dynamic photosynthesis under the conditions used. In Chapter 1, the rationale for the research conducted is described, by introducing the concept of fluctuating irradiance and its effects on photosynthesis rates. The chapter discusses how dynamic photosynthesis is measured and described, and provides a range of possible applications of the insights gained by the research conducted in this dissertation. In Chapter 2, the current literature is reviewed and a mechanistic framework is built to explore the effects that the environmental factors CO2 concentration, temperature and air humidity have on rates of dynamic photosynthesis. Across data from literature, higher CO2 concentration and temperature speed up photosynthetic induction and slow down its loss, thereby facilitating higher rates of dynamic photosynthesis. Major knowledge gaps exist regarding the loss of photosynthetic induction in low irradiance, dynamic changes in mesophyll conductance, and the extent of limitations imposed by gs across species and environmental conditions. Chapter 3 is an experimental exploration of the effects of CO2 concentration, leaf temperature, air humidity and percentage of blue irradiance on rates of photosynthetic induction in dark-adapted tomato leaves. Rubisco activation, changes in stomatal and mesophyll conductance, diffusional and biochemical limitations, efficiency of electron transport through photosystem II, NPQ and transient water use efficiency, were examined to give a comprehensive overview of the environmental modulation of dynamic photosynthesis. Unlike the percentage of blue irradiance, increases in CO2 concentration, leaf temperature and air humidity all positively affected the rates of photosynthetic induction, and these effects were explained by changes in diffusional and biochemical limitations. Maximising the rates of Rubisco activation would increase CO2 assimilation by 6-10%, while maximising the rates of stomatal opening would increase assimilation by at most 1-2%, at the same time negatively affecting intrinsic water use efficiency. In Chapter 4 it is explored whether the effects of CO2 concentration on dynamic photosynthesis are similar across various irradiance environments. Gain and loss of photosynthetic induction in several low irradiance treatments, as well as sinusoidal changes in irradiance, were studied using tomato leaves. Elevated CO2 concentration (800 ppm) enhanced the rate of photosynthetic induction by 4-12% (compared to 400 ppm) and decreased the loss of photosynthetic induction by 21-25%. Elevated CO2 concentration enhanced rates of dynamic photosynthesis regardless of initial photosynthetic induction state to a similar extent. Therefore, rising global CO2 concentration will benefit integrated assimilation throughout whole canopies, where different leaf layers experience widely differing irradiance regimes. In Chapter 5 it is tested whether stomatal limitation exists during photosynthetic induction in tomato leaves. The abscisic acid-deficient flacca mutant and its wildtype were exposed to various CO2 concentrations to change the diffusion gradient. Despite gs being much larger in flacca, photosynthetic induction proceeded with the same speed in both genotypes in ambient CO2 concentration. This suggested that stomata did not limit photosynthetic induction in the wildtype. Using these findings, several indices of stomatal limitations were compared. Diffusional limitation, a new index, was found to be the most useful. In Chapter 6, an exploration of some physiological limitations underlying dynamic photosynthesis is undertaken. Several mutants, transformants and ecotypes of A. thaliana, affecting rates of Rubisco activation, gs, NPQ and sucrose metabolism, were used. Next to a characterisation of their steady-state responses to CO2 concentrations and irradiance, leaves were exposed to stepwise increases and decreases in irradiance (using several intensities) and to lightflecks of several amplitudes and frequencies. Rubisco activase isoform and concentration, as well as various levels of gs, strongly affected rates of dynamic photosynthesis, while this was not the case with low NPQ or sucrose phosphate synthase concentration. This suggests Rubisco activase and gs as targets for improvement of photosynthesis in fluctuating irradiance. Chapter 7 is a modelling exercise of dynamic photosynthesis, based on data obtained from measurements on mutants of A. thaliana (Chapter 6). This includes a goal-seeking model that allows reproducing the regulation of Rubisco by irradiance and CO2 concentration. The model also includes a full description of leaf-level NPQ, incorporates mesophyll conductance and accounts for the fundamental physics of delays introduced by open gas exchange systems on CO2 measurements. Different data sets for model calibration and validation were used. It was found that the model accurately predicted the effects of the mutants, suggesting that the assumptions of the model were sound and represented the underlying mechanisms correctly. In Chapter 8, the findings in this thesis are synthesized. The insights gained throughout this dissertation are related to existing literature to give a comprehensive overview of the state of knowledge about the limitations of dynamic photosynthesis. The methodology of assessing transient stomatal limitations, and some aspects of using chlorophyll fluorescence measurements during photosynthetic induction, are discussed. Finally, possible applications and ideas for future research on photosynthesis in fluctuating irradiance are discussed.

Fogging, misting, roof sprinklers, pad-and-fan and other techniques based on water evaporation are effective tools for improving the growing conditions in a greenhouse when humidity is low. They should be used wisely though.

Teken zijn een belangrijke vector in de overdracht van de ziekte van Lyme op mensen. De overleving enhet gedrag van teken zou beïnvloed kunnen worden door de manipulatie van hun microhabitat. In eenexperiment zijn we dat nagegaan. De mortaliteit van de teek blijkt negatief gecorreleerd te zijn aan derelatieve luchtvochtigheid en temperatuur en het gedrag positief aan de temperatuur. In het beheer vannatuurgebieden kan hier op worden ingespeeld.

Schade aan kasgewassen door Botrytisaantasting (smet) is één van de belangrijkste knelpunten in de kasteelt. Te hoge luchtvochtigheid en lokale koude plekken met condensvorming zijn de belangrijkste oorzaken van smet. Het instellen van een droog kasklimaat kost veel energie, maar door het gebruik van een waarschuwings- of sturingsmodel is het mogelijk om naast het vermijden van besmetting straks ook energiewinst te behalen ten opzichte van telen zonder model. Met verklarende computermodellen kunnen plantengroei, -kwaliteit en schimmelinfectie berekend worden. De modellen kunnen Botrytis helpen voorkomen door de juiste klimaatinstellingen en de inrichting van de kas.

Door op twaalf bedrijven in drie meetronden van zes weken wekelijks te oogsten en de gerealiseerde klimaatdata te analyseren bleek dat het microklimaat rond de plant van grote invloed was op het ontstaan van pokken in de naoogstfase. Hoe vochtiger het is, hoe groter de snelheid van Botrytisontwikkeling. Overdag moeten de omstandigheden rond de bloem zodanig zijn dat sporen òf doodgaan (lage vochtigheid, hoge temperatuur), òf niet kunnen hechten (lage vochtigheid) of verspreid worden. ‘s Nachts moet de vochtigheid tussen de bladeren niet te hoog oplopen om groei en ontwikkeling van de schimmel te remmen.

Om inzicht te krijgen in het effect van nieuwe belichtingssystemen op de productie, is Gerbera, cv. Kimseywerd gekweekt onder SON-T (13 uur dag), hybride (9-12 uur dag) en onder LED (10.5 uur dag) belichting, metoplopende etmaaltemperaturen. Het teeltsysteem met SON-T belichting bij koudere dag- en nachttemperaturenpresteerde lange tijd het beste voor wat betreft bloemproductie in vergelijking met de hybride en LEDbehandeling. Het lijkt er sterk op dat een voldoende lage etmaaltemperatuur, onder de 16°C, een versterkendeffect heeft op de generativiteit van een Gerbera gewas. Daglengte lijkt dan tot zekere hoogte ondergeschikt tezijn voor wat betreft aanleg van knoppen en scheuten. Een lagere kastemperatuur resulteerde in een langereuitgroeiduur van de bloemen met 2 dagen. Er kan veel energie bespaard worden bij de Gerberateelt. T.a.v.de referentie werd aan elektrische energie bespaard bij SON-T (28%), hybride (35%) en LED (41%), en voorwat betreft warmte energie bij SON-T (71%), hybride (59%) en LED (36%). Het totaal energiebesparing aanelektrische en warmte energie tezamen was voor SON-T 48%, hybride 46% en voor LED 39%. Het aantalGerbera taken dat geproduceerd werd per eenheid primaire energie was 18.6, 19.8 en 17.2 voor SON-T, hybrideen de LED teeltconcepten, respectievelijk.

A combination of an air handling unit and an additional screen installation, has been tested at the chrysanthemums nursery Arcadia. With this air handling unit the humidity turned out to be controlled very accurately, which provided the opportunity to use less heat and to incrementally accept a higher RV. The combination with an extra screen installation implied 30% less use of heat compared to the adjacent reference site.

A consortium of companies, together with Wageningen UR, is developing a greenhouse that will maximise the amount of light entering between October and March. The goal is to achieve 10% extra yield during these months. The gain in light should come from a combination of various adjustments and improvements. Following the theoretical simulation models and physical scale models, the first winter-light greenhouse will be built next year as ‘proof of principle’ at the Innovation- and Demonstration centre in Bleiswijk, the Netherlands.

A combination of an air handling unit and an additional screen installation, has been tested at the chrysanthemums nursery Arcadia. With this air handling unit the humidity turned out to be controlled very accurately, which provided the opportunity to use less heat and to incrementally accept a higher RV. The combination with an extra screen installation implied 30% less use of heat compared to the adjacent reference site. In de praktijk moet worden aangetoond dat met geringe middelen veel op de warmtevraag kan worden bespaard met behoud van een gezond en productief gewas. Bij aanvang van het project zijn daarom drie doelen gesteld. • Een breed gedragen opzet voor een energiezuinige chrysantenteelt met verhoging van de teeltzekerheid. • Door deze opzet moet het warmtegebruik met minstens 9 m3/m2.jaar (ongeveer 30%) kunnen worden verminderd. De 30% besparing op warmte zal vooral basislast betreffen. • De kennis moet ook toepasbaar zijn voor andere belichte en geschermde teelten.

Om inzicht te krijgen in het effect van nieuwe belichtingssystemen op de productie, is Gerbera, cv. Kimseywerd gekweekt onder SON-T (13 uur dag), hybride (9-12 uur dag) en onder LED (10.5 uur dag) belichting, metoplopende etmaaltemperaturen. Het teeltsysteem met SON-T belichting bij koudere dag- en nachttemperaturenpresteerde lange tijd het beste voor wat betreft bloemproductie in vergelijking met de hybride en LEDbehandeling. Het lijkt er sterk op dat een voldoende lage etmaaltemperatuur, onder de 16°C, een versterkendeffect heeft op de generativiteit van een Gerbera gewas. Daglengte lijkt dan tot zekere hoogte ondergeschikt tezijn voor wat betreft aanleg van knoppen en scheuten. Een lagere kastemperatuur resulteerde in een langereuitgroeiduur van de bloemen met 2 dagen. Er kan veel energie bespaard worden bij de Gerberateelt. T.a.v.de referentie werd aan elektrische energie bespaard bij SON-T (28%), hybride (35%) en LED (41%), en voorwat betreft warmte energie bij SON-T (71%), hybride (59%) en LED (36%). Het totaal energiebesparing aanelektrische en warmte energie tezamen was voor SON-T 48%, hybride 46% en voor LED 39%. Het aantalGerbera taken dat geproduceerd werd per eenheid primaire energie was 18.6, 19.8 en 17.2 voor SON-T, hybrideen de LED teeltconcepten, respectievelijk.

Wageningen UR Greenhouse Horticulture made an inventarisation of knowledge about evaporation in greenhouses regarding to energy saving. Evaporation is especially effective on the energy balance and water transport in the plant. The limitation of the evaporation in the night will have an effect on the water uptake by the roots, and thus on the Ca uptake. A too low absorption of water during the night will manifest itself in the first place in a lack of Ca related problem. The energy balance and a balance of moisture stress by affecting the plant through the stomata opening and have through that affect CO2 uptake. There is no single factor which can be used as a strong steering factor oriented to align the stomata in the night. Knowledge gaps around the water absorption and evaporation in the night are: how long can we permit a situation of high humidity in the early night; how can we steer water uptake by EC in relation to changes in weather; how can we optimize root activity and substrate volume; what is the minimum evaporation for Ca uptake during the night? In practice, minimizing evaporation means growing at higher humidity, with high isolation and little air movement. Wageningen UR Glastuinbouw heeft in opdracht van Kas als Energiebron een inventarisatie in de literatuur en in lopende kasproeven gedaan, naar het verlagen van de verdamping om energie te besparen. Verdamping heeft vooral effect op de energie balans en het watertransport in de plant. De beperking van de verdamping in de nacht zal effect hebben op de wateropname door de wortel en daarmee op de Calcium opname. Een te geringe wateropname in de nacht zal zich in de eerste plaats uiten in een aan Ca gebrek gerelateerd probleem. De energiebalans en een balans van de vochtspanning zijn door de plant te beïnvloeden via de huidmondjesopening en hebben via die weg invloed op de CO2 opname. In de nacht is opname van CO2 niet van belang. Er is niet één factor die als sterke stuurfactor gebruikt kan worden om huidmondjes in de nacht gericht te laten sluiten. Kennislacunes rond de wateropname en verdamping in de nacht zijn: hoe lang mag een periode met hoge luchtvochtigheid aan het begin van de nacht duren, hoe kan de wateropname via de EC in relatie tot weerovergangen gestuurd worden, hoe kunnen de wortelactiviteit en het substraatvolume geoptimaliseerd worden, en wat moet de minimale verdamping in de nacht zijn voor de minimaal benodigde opname van Ca. In de praktijk zal minimaliseren van verdamping betekenen dat er vochtiger, met veel isolatie en weinig luchtbeweging geteeld moet worden.

Wageningen UR Greenhouse Horticulture made an inventarisation of knowledge about evaporation in greenhouses regarding to energy saving. Evaporation is especially effective on the energy balance and water transport in the plant. The limitation of the evaporation in the night will have an effect on the water uptake by the roots, and thus on the Ca uptake. A too low absorption of water during the night will manifest itself in the first place in a lack of Ca related problem. The energy balance and a balance of moisture stress by affecting the plant through the stomata opening and have through that affect CO2 uptake. There is no single factor which can be used as a strong steering factor oriented to align the stomata in the night. Knowledge gaps around the water absorption and evaporation in the night are: how long can we permit a situation of high humidity in the early night; how can we steer water uptake by EC in relation to changes in weather; how can we optimize root activity and substrate volume; what is the minimum evaporation for Ca uptake during the night? In practice, minimizing evaporation means growing at higher humidity, with high isolation and little air movement.

Varens wijken in veel opzichten af van andere potplanten. Ze vormen geen bloemen en de voortplanting is een ingewikkelde zaak. Ook inwendig kennen ze tal van bijzonderheden. Daarom is het des te verwonderlijker dat ze op de bedrijven gewoon tussen andere groene planten kunnen worden geteeld.

An epidemiological study was carried out to explore the relationship between climatic factors and non-specific low-back and neck-shoulder symptoms in working populations. In a review of published literature, 27 studies were found which related climatic factors to musculoskeletal symptoms, but none of these studies specifically addressed the subject. It can be concluded that a relationship between climatic factors and musculoskeletal symptoms is considered at least plausible by both researchers, workers and patients, but that the epidemiological evidence appearing from literature is very weak. Questionnaire data which were collected on musculoskeletal symptoms, workload and perceptions of climatic conditions of 2030 workers in 24 different occupations were analysed multi-variately. About one-quarter of the workers related symptoms of the low back and neck-shoulders to climatic factors. They perceived climatic factors in most cases as aggravating factors for their symptoms. No seasonal influence on prevalence rates was reported. For low-back and neck-shoulder symptoms and for sick leave due to neck-shoulder symptoms, an association was found with climatic factors, and in particular with respect to draughts in relation to neck-shoulder symptoms. In addition, neck-shoulder symptoms were negatively related to frequent outdoor work. The findings suggest a relationship between climatic factors and musculoskeletal symptoms and call for further detailed investigations.

Onderzoekers van Wageningen UR Glastuinbouw hebben in het kader van het Gezonde Kas-project voor het eerst het klimaat geregeld op basis van meerdere draadloze sensoren voor temperatuur en luchtvochtigheid. Doel was om de klimaatcomputer te laten sturen op basis van het punt in de kas waar het laagste dauwpunt gemeten werd. Omdat het klimaat in de kas van plek tot plek en in de tijd kan variëren, zal dat dus niet altijd dezelfde plek zijn. Op die manier ontstaat een regeling waarbij de meetbox als het ware kan wandelen.

Zaden zijn het beste houdbaar als je ze koel en droog bewaart. Maar het kan nog veel beter: zuurstofloos. Dat toont onderzoek van Steven Groot (PRI) en collega’s aan.

Onderzoekers van Wageningen UR Glastuinbouw hebben in het kader van het Gezonde Kas-project voor het eerst het klimaat geregeld op basis van meerdere draadloze sensoren voor temperatuur en luchtvochtigheid. Doel was om de klimaatcomputer te laten sturen op basis van het punt in de kas waar het laagste dauwpunt gemeten werd. Omdat het klimaat in de kas van plek tot plek en in de tijd kan variëren, zal dat dus niet altijd dezelfde plek zijn. Op die manier ontstaat een regeling waarbij de meetbox als het ware kan wandelen.

Teken zijn een belangrijke vector in de overdracht van de ziekte van Lyme op mensen. De overleving enhet gedrag van teken zou beïnvloed kunnen worden door de manipulatie van hun microhabitat. In eenexperiment zijn we dat nagegaan. De mortaliteit van de teek blijkt negatief gecorreleerd te zijn aan derelatieve luchtvochtigheid en temperatuur en het gedrag positief aan de temperatuur. In het beheer vannatuurgebieden kan hier op worden ingespeeld.

Het onderzoek in dit rapport maakt onderdeel uit van het programma Kas als Energiebron. Binnen dit programma valt dit onderzoek onder het transitie pad teeltstrategieën. Doel van dit programma is dat bestaande glastuinbouwbedrijven kunnen profiteren van nieuwe inzichten en zo zonder hoge investeringen kunnen besparen op het energieverbruik. Specifieke gewassen kennen ook specifieke knelpunten. In de relatief koude teelten Freesia en Anjer loopt, door de lage teelttemperatuur, de luchtvochtigheid al snel op, wat een knelpunt vormt voor de toepassing van maatregelen uit Het Nieuwe telen. Er kan energie bespaard worden door de kas beter te isoleren en de luchtramen meer gesloten te houden, maar dan moet er een oplossing gevonden worden voor de oplopende luchtvochtigheid. De potentiele energiebesparing door betere isolatie en vochtbeheersing bij Freesia werd geschat op 7 m3 /m2/jaar (50%, excl. stomen en belichting) op het totaal bedrijfsverbruik, maar dit is afhankelijk van de effecten op het gewas. Dit project moest meer duidelijkheid geven over de kwantitatieve effecten van actieve ontvochtiging en het afdekken van de bodem op de gewasgroei van Freesia, het beperken van de verdamping en de thermische isolatie.

Zaden zijn het beste houdbaar als je ze koel en droog bewaart. Maar het kan nog veel beter: zuurstofloos. Dat toont onderzoek van Steven Groot (PRI) en collega’s aan.

SensorTagSolutions ontwikkelde een goedkoop meetsysteem, AquaTag, zodat meer kraanvakken kunnen worden voorzien van sensoren. Drie boomkwekers in regio Boskoop testen het systeem met hulp van PPO.

Horticulture production in Malaysia is located mainly in the highlands. Further expansion in this area is not possible. Growers are having to move to the lowlands, but the particularly high temperatures and humidity make this area less favourable for greenhouse cultivation. A recent study by Wageningen UR Greenhoude Horticulture in the Netherlands however, demonstrated that greenhouse production is certainly possible in this area, if good use is made of technical possibilities.

A consortium of companies, together with Wageningen UR, is developing a greenhouse that will maximise the amount of light entering between October and March. The goal is to achieve 10% extra yield during these months. The gain in light should come from a combination of various adjustments and improvements. Following the theoretical simulation models and physical scale models, the first winter-light greenhouse will be built next year as ‘proof of principle’ at the Innovation- and Demonstration centre in Bleiswijk, the Netherlands.

Na twee zomers met hoge buitentemperaturen over lange(re) periodes is er veel aandacht voor koelinstallaties in de vleeskuikensector. Deze installaties maken gebruik van het koelende effect van het verdampen van water door het water te vernevelen in de stal. In dit artikel wordt ingegaan op de mogelijkheden van deze apparatuur, de voor- en nadelen en de aandachtspunten bij gebruik. Voor een goed inzicht in het gebruik is ook informatie opgenomen over theoretische achtergronden van het verdampen van water in lucht.

Elk bewaarseizoen kent zijn bijzonderheden, zo ook seizoen 2004-2005. Dit werd gekenmerkt dooe schilvlekjes die al vroeg in het seizoen ontstonden, maar ook de goede tot zeer goede uitstalkwaliteit van Elstar. Bij Conference kwamen slappe nekken dankzij de extra aandacht voor dit probleem nauwelijks voor. Dit terwijl juist bij Elstar meer dan normaal werd gereclameerd over een 'slappere' appel. In dit artikel een terugblik en adviezen voor het nieuwe bewaarseizoen