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Niels Ehler and Jesper M. Aaslyng

The possibility of constructing an Internet application that would enable greenhouse users to track climate and control parameters from any Internet-connected computer was investigated. By constructing a set of HTML-templates, dynamic information from the control-system databases was integrated in real-time, and was uploaded to a common net-server by automatic generation of web pages using software developed during the project. Good performance, reliability and security were obtained and the technology proved to be an efficient way of supplying a broad range of users not only with climatic data but also with results from ongoing research.

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Lise T. Jensen, Jesper M. Aaslyng and Eva Rosenqvist

A daylight climate chamber was designed with the aim of testing new greenhouse climate control strategies on a small scale. Precise control and measure ment of the chamber climate and long-term measurement of canopy carbon dioxide (CO2) exchan ge was possible. The software was capable of simulating a climate computer used in a full-scale greenhouse. The parameters controlled were air temperature, CO2 concentration, irradiance, air flow, and irrigation. The chamber was equipped with a range of sensors measuring the climate in the air of the chamber and in the plant canopy. A chamber perfor mance experiment with chrysanthemum (Chrysanthemum grandiflorum `Coral Charm') plants grown in perlite was carried out over the course of 3 weeks. Five air temperature treatments at a day length of 13 hours were carried out, all with the same 24-hour mean temperature of 20 °C, but different day temperatures (18.0 to 25.1 °C) and night temperatures (14.0 to 22.4 °C). Rate of canopy CO2 exchange in the chambers was calculated. In the range of day temperatures used, rates of canopy photosynthesis were almost equal. The results showed that leaf area and plant dry weight after 3 weeks were not significantly different among temperature treatments, which is promising for further investigations of how climate control can be used to decrease energy consumption in greenhouse production.

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Lene Jakobsen, Michael Brogaard, Annie Enkegaard, Henrik F. Brødsgaard and Jesper M. Aaslyng

Dynamic climate regimes have been developed mainly to reduce energy consumption in the greenhouse, and this has been the main reason for their adoption by growers. During recent years, Danish growers have observed that problems with pests have diminished since they changed from the traditional rigid climate regime to a dynamic regime. The trend has also been observed in scientific experiments testing different dynamic climate regimes. The present experiment shows that the influx of thrips from outside into the greenhouse was reduced by 40% under a dynamic climate regime compared to a traditional rigid regime, and that this was related to the opening degree of the vents. Vents were open on average 7% under the dynamic regime and 33% in the traditional climate. The influx of thrips was linearly correlated with density outside the greenhouse (P < 0.0001) and with opening degree of the vents (P = 0.0001).

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Jakob Markvart, Eva Rosenqvist, Helle Sørensen, Carl-Otto Ottosen and Jesper M. Aaslyng

There is increasing use of electricity for supplemental lighting in the northern European greenhouse industry. One reason for this may be to secure a high growth rate during low-light periods by an attempt to increase net photosynthesis. We wanted to clarify which period of the day resulted in the best use of a 5-h supplemental light period for photosynthesis and growth. The periods tested were supplemental light during the night, day, morning, and evening. The experiments were carried out in daylight climate chambers measuring canopy gas exchange. The air temperature was 25 °C and the CO2 level ≈900 ppm. Vegetative chrysanthemum was used, because this species responds quickly to change in light level. The leaf areas of the plant canopies were nondestructively measured each week during the 4-week experimental period. The fact that the quantum yield of photosynthesis is greater at low than at high light intensities favors the use of supplemental light during the dark period, but growth measured as dry weight of the treated plants at the end of the experiments was not significantly different given identical light integrals of the treatments. However, one experiment indicated that increased time with dark hours during day and night (24 h) might decrease net photosynthesis. The assimilation per unit leaf area was approximately the same during times of sunlight through a diffusing screen at 100 μmol·m−2·s−1 of photosynthetic photon flux (PPF) as during times of supplemental (direct) light application at PPF of 200 μmol·m−2·s−1 by high-pressure sodium lamps. We conclude that during the winter and periods of low light intensities, the daily carbon gain does not depend on the time of supplemental light application, but is linked to the total light integral. However, extended time with dark hours during day and night (24 h) might be a disadvantage because of longer periods with dark respiration and subsequent loss of carbon. Our results indicate that during times of low light conditions, it is not necessary to include factors such as the timing of supplemental lighting application to achieve higher net photosynthesis in climate control strategies.