Growers have often assumed that a 1% increment in light results in a 1% yield increase. In this study, this rule of thumb has been evaluated for a number of greenhouse grown crops: fruit vegetables (cucumber, tomato, sweet pepper), soil grown vegetables (lettuce, radish), cut flowers (rose, chrysanthemum), bulb flowers (freesia, lily), flowering pot plants (poinsettia, Kalanchoe), and non-flowering pot plants (Ficus, Dracaena). A literature survey was first carried out on the effects of light on growth, dry matter production and partitioning, dry matter content and harvestable yield. Subsequently, yield data for cucumber, poinsettia and rose from commercial growers were analysed. Finally, growers were interviewed to assess their crop management in relation to the available light. For most crops a 1% light increment results in 0.5 to 1% increase in harvestable product. As a rule of the thumb the following values may be used: 0.8-1% for soil grown vegetables, 0.7-1% for fruit vegetables, 0.6-1% for cut flowers, 0.25-1.25 for bulb flowers, 0.5-1% for flowering pot plants and 0.65% for non-flowering pot plants. These are average values, which depend on several factors. For instance, the relative effect of light on growth is greater at lower light levels, at higher CO 2 concentrations and at higher temperatures. Consequently, the relative effect is larger in winter than in summertime. The effect of light on growth also depends on the duration and moment that the light level is changed. Besides a positive effect on yield quantity, light usually has a positive effect on quality as well. Light should not be considered as a separate growth factor in greenhouse horticulture, as it forms an integral part of the total farm management. Many growers, for instance, choose a higher temperature and adapt their plant density and cultivar choice when the light level is increased. INTRODUCTIONThe growth rate of a crop largely depends on the radiation it receives. Considering a given solar radiation, the grower has several options to increase the amount of incident light on a crop, such as building a greenhouse with high light transmissivity, or using assimilation light. On the other hand, the use of some measures such as screens may reduce the amount of incident light on the crop.In order to judge whether a measure affecting the light intensity is profitable, the grower needs to estimate its effect on production. For more than 20 years Dutch growers have usually taken a 1% additional light results in 1% additional growth and production as a rule of thumb. For cut flowers and pot plants there are indications that effects of light on production are less strong than in vegetable crops; for these crops 1% additional light it is often assumed to result in 0.5% additional growth and production.Light is the driving force for photosynthesis, while it may also affect plant development, morphology, dry matter partitioning and water content. Despite the assumed proportionality between light and production, it is well known that leaf p...
The so-called closed greenhouse (closed ventilation windows) is a recent innovation in Dutch greenhouse industry. The technical concept consists of a heat pump, underground (aquifer) seasonal energy storage as well as daytime storage, air treatment units with heat exchangers, and air distribution ducts. Savings of up to 30% in fossil fuel and production increases by up to 20%, mainly because of the continuously high CO 2 concentration, have been reported. Economic feasibility of this innovative greenhouse highly depends on the yield increase that can be obtained. In this simulation study the effects of greenhouse climate on tomato yield in a closed greenhouse are presented. The explanatory model INTKAM was used, which has several submodels e.g. for light interception, leaf photosynthesis and biomass partitioning. The closed greenhouse offers possibilities for combinations of light, temperature, air humidity and CO 2 concentration that are impossible in a conventional greenhouse. At high CO 2 concentration and high light intensity, leaf photosynthesis shows a more narrow optimum for temperature than at high CO 2 and moderate light intensity. However, the response of crop photosynthesis to temperature has a much broader optimum than that of leaf photosynthesis. Besides photosynthesis, temperature also influences aspects like partitioning, leaf area development and fruit development. Yield potential reduces at temperatures above 26 o C, with fruit set being one of the first processes that is negatively influenced by supra-optimal temperatures. Based on actual climatic conditions in a conventional and a closed greenhouse (same crop management) measured during two years, INTKAM predicts an increase in yield by about 17%. Hence, in a closed greenhouse a higher stem density can be maintained for obtaining the same average fruit weight (size) as in a conventional greenhouse. In 2005 actual yield increase was similar to the simulated one (16%), but in 2004 only a 9% higher yield was realized, at least partly because of botrytis infection in the closed greenhouse.
Growers and Dutch government have concluded a covenant in which they express the ambition to reduce the carbon footprint of greenhouse production in order to improve the energy neutrality of newly built greenhouses. Conditioned cultivation in (semi-)closed greenhouses is seen as one of the instruments to reach this goal. It is appointed in the covenant to arrive in 2011 at 700 ha and in 2020 at 2,500 ha semi-closed greenhouses. This paper describes the instruments used to monitor the results of conditioned cultivation in eight semi-closed greenhouses in practice. It addresses the monitoring process, the installations involved and highlights some of the measured data.
Bij het Delphy Improvement Centre zijn in 2017 met financiering van Kas als Energiebron, ChrIP en leveranciers, vier chrysantenteelten uitgevoerd met de volgende doelstellingen: • Een warmtegebruik van maximaal 15 m 3 /m 2 .jaar aan aardgasequivalenten (ae). • Deze warmte dient volledig te worden onttrokken uit warmteoogst (koeling). • Een CO 2-gebruik van 25 kg/m 2 .jaar. • Een elektriciteitsgebruik voor belichting van 121 kWh/m 2. • 5% meer productie ten opzichte van de praktijk. De belangrijkste middelen om deze doelstelling te bereiken zijn hybride belichting, diffuus glas met 2 ARcoatings, een extra energiedoek, 8 luchtbehandelingskasten, een warmtepomp en bronpompen. De teelten zijn uitgevoerd onder de naam 'De Perfecte Chrysant' (DPC). De gerealiseerde gebruiken van CO 2 en vooral warmte blijken lager te zijn dan de doelstelling. De hoeveelheid geoogste warmte (koeling) is veel hoger en de hoeveelheid belichting is vrijwel gelijk aan de doelstelling. Geconcludeerd wordt dat het technisch mogelijk is om met een investering in luchtbehandelingskasten, warmtepomp en bronpompen, een extra scherm en LED belichting chrysanten kunt telen zonder gas (behalve voor het stomen).
Bij het Delphy Improvement Centre zijn in 2017 en 2018 met financiering van Kas als Energiebron, ChrIP en leveranciers, negen chrysantenteelten uitgevoerd met de volgende doelstellingen: • Een warmtegebruik van maximaal 15 m 3 /(m 2 .jaar) aan aardgasequivalenten (ae). • Deze warmte dient volledig te worden onttrokken uit warmteoogst (koeling) en de elektriciteit voor de warmtepomp. • Een CO 2-gebruik van 25 kg/(m 2 .jaar). • Een elektriciteitsgebruik voor belichting van 121 kWh/(m 2 .jaar). • 5% meer productie ten opzichte van de praktijk. De belangrijkste middelen om deze doelstelling te bereiken zijn hybride belichting, diffuus glas met 2 ARcoatings, een extra energiedoek, luchtbehandelingskasten, een warmtepomp en bronpompen. De teelten zijn uitgevoerd onder de naam 'De Perfecte Chrysant' (DPC). De gerealiseerde gebruiken van warmte blijken lager te zijn dan de doelstelling. De hoeveelheid geoogste warmte (koeling) is juist veel hoger en de belichting is in de loop van het project steeds vaker ingezet. Verneveling heeft de hoeveelheid warmteoogst verhoogd. De 5% hogere productie is slechts bij drie van de negen teelten gelukt en na aanvankelijke kritiek is de kwaliteit van de takken in de loop van het project steeds beter beoordeeld. Geconcludeerd wordt dat het technisch mogelijk is om met een investering in luchtbehandelingskasten, warmtepomp en bronpompen, een extra scherm en hybride belichting chrysanten te telen zonder gas (behalve voor het stomen).
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