Long time plant response measurements for yield prediction, water use and climate control optimization using gas exchange measurements in semi closed and ventilated greenhouses

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An advanced prototype of a phytomonitor was developed at Humboldt University in the frame of the national ZINEG project for low energy greenhouses ( Ten leaf cuvettes were allocated to different tomato leaves in the canopy to get a representative average of the gas exchange of younger and older leaves under shaded and non-shaded conditions. The cuvettes were constantly attached to several plants for the whole cultivation period, with a seven-day interchange period. Two instruments were used in two greenhouses with different climate control systems (semi-closed and a ventilated greenhouse as reference) to show the differences in the climate – canopy interaction. With the help of the Mollier Plot Analyzer software, developed at Humboldt University, the climate comfort zone of the canopy for maximum photosynthetic light use efficiency was found. With the calculation of the accumulated CO2 and transpired water, the differences in the yield expectation for the next four weeks and the plant consumed water was estimated. From the result of the light use efficiency evaluation with the Mollier Plot Analyzer, the comfort zone for tomato growing in the semi-closed greenhouse was estimated to be in a temperature range from 20 to 28°C, with a relative humidity of 75 to 95%. In the ventilated greenhouse most of the condition points with lower light use efficiency were found to have higher temperature and lower relative humidity. The difference in the yield between the semi-closed and ventilated greenhouse was shown by the difference in CO2 uptake measured by the phytomonitors and the difference in the photosynthetic light use efficiency of the canopy in both greenhouses. The calculated water consumption using the gas exchange measurement data showed a high correlation to the measured water consumption. With this result it should be possible to apply gas exchange measurement systems not only for climate control but also for irrigation control.

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... Kläring and Krumbein (2013)). Methods that mechanically attach the measurement device to the leaves are better suited for autmated climate control, although they are expensive and need to be relocated as the plants grow (Schmidt, 1992;Schmidt et al., 2014). ...
Moderne Präzisionsgartenbaulicheproduktion schließt hoch technifizierte Gewächshäuser, deren Einsatz in großem Maße von der Qualität der Sensorik- und Regelungstechnik abhängt, mit ein. Zu den Regelungsstrategien gehören unter anderem Methoden der Künstlichen Intelligenz, wie z.B. Künstliche Neuronale Netze (KNN, aus dem Englischen). Die vorliegende Arbeit befasst sich mit der Eignung KNN-basierter Modelle als Bauelemente von Klimaregelungstrategien in Gewächshäusern. Es werden zwei Modelle vorgestellt: Ein Modell zur kurzzeitigen Voraussage des Gewächshausklimas (Lufttemperatur und relative Feuchtigkeit, in Minuten-Zeiträumen), und Modell zur Einschätzung von phytometrischen Signalen (Blatttemperatur, Transpirationsrate und Photosyntheserate). Eine Datenbank, die drei Kulturjahre umfasste (Kultur: Tomato), wurde zur Modellbildung bzw. -test benutzt. Es wurde festgestellt, dass die ANN-basierte Modelle sehr stark auf die Auswahl der Metaparameter und Netzarchitektur reagieren, und dass sie auch mit derselben Architektur verschiedene Kalkulationsergebnisse liefern können. Nichtsdestotrotz, hat sich diese Art von Modellen als geeignet zur Einschätzung komplexer Pflanzensignalen sowie zur Mikroklimavoraussage erwiesen. Zwei zusätzliche Möglichkeiten zur Erstellung von komplexen Simulationen sind in der Arbeit enthalten, und zwar zur Klimavoraussage in längerer Perioden und zur Voraussage der Photosyntheserate. Die Arbeit kommt zum Ergebnis, dass die Verwendung von KNN-Modellen für neue Gewächshaussteuerungstrategien geeignet ist, da sie robust sind und mit der Systemskomplexität gut zurechtkommen. Allerdings muss beachtet werden, dass Probleme und Schwierigkeiten auftreten können. Diese Arbeit weist auf die Relevanz der Netzarchitektur, die erforderlichen großen Datenmengen zur Modellbildung und Probleme mit verschiedenen Zeitkonstanten im Gewächshaus hin.
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A semi-closed solar collector greenhouse was tested to evaluate the yield and the energy saving potential compared with a commercial greenhouse. As such, new algorithm for ventilation, carbon dioxide (CO2) enrichment, as well as for cooling and heating purposes initiated by a heat pump, cooling fins under the roof and a low temperature storage tank were developed. This cooling system showed that the collector greenhouse can be kept longer in the closed operation mode than a commercial one resulting in high levels of CO2 oncentrations, relative humidity and temperatures. Based on these conditions, the potosynthesis and associated CO2 fixations within the plant population were promoted during the experiment, resulting in a yield increase by 32%. These results were realized, although the mean light interception by energy screens and finned tube heat exchangers was increased by 11% compared to the reference greenhouse. The energy use efficiency was improved by 103% when the collector greenhouse was considered as energy production facility. In this context, the energy saving per kilogram produced tomatoes in the collector greenhouse is equivalent to the combustion of high amounts of different fossil fuels, where the reduced CO2 emissions ranged between 2.32 kg and 4.18 kg CO2 per kg produced tomatoes. The generated total heat was composed of approximately one-third of the latent heat and over two-thirds of the sensible heat, where a maximum collector efficiency factor of 0.7 was achieved.
A newly developed device for measuring transpiration flows on several leaves in a plant stand was used to test the possibility for controlling the water supply of greenhouse plants. For this, the time integral is formed for the measured transpiration mass flow density. That integral is then extrapolated to the entire area of the plant stand, using the leaf area/floor space index (LAI). As soon as a defined transpiration sum is reached, an irrigation run is triggered to give that amount of water back to the plants. For testing the method, the water balance was determined for plant stands. Measurement on strongly transpiring plants (Capsicum annuum) indicated regular variations of the water balance at night. Errors due to differences between cuvettes and reference sensor were eliminated after the measuring system was modified. Good agreement between the amounts of water supplied and the sum of transpiration rate and excess water were found in gerbera plants grown in perlite. As a second stage of the experiment, plant stands were controlled with the help of the measured transpiration. In stands with constant leaf area/floor space ratios, the trend of tension oscillations in the substrate was kept constant over several days. Variations appeared when the leaf area index changed due to plant growth. To eliminate that effect, irrigation based on the measured transpiration was adjusted with a growth model, or the trend of tension was recorded for adjustment of the leaf area index.
A two-stage experiment was performed to determine the influence of a high-pressure fog system on the CO2 concentration and gas exchange efficiency (GEE) in greenhouses with CO2 enrichment. The experiments were carried out with tomatoes (Lycopersicon esculentum). Photosynthetic GEE was introduced as a new evaluative quantity to represent the short-term CO 2 uptake capacity of the plant canopy. The physiological data for the plants were measured with a phytomonitoring system. The ratio between the measured and the calculated CO2 uptake GEE was calculated and coded on a color scale. With the Mollier plot method, ranges with a maximum GEE can be located for several temperatures and relative humidities. Plant yields and quality were also recorded. A preliminary test identified an increase in GEE with higher relative humidity, with a dependence on leaf transpiration (r 2 = 0.56). In the main experiment, the effects of the combined application of fog and CO2 enrichment were estimated. A higher diurnal average CO2 content was observed in the fog cabin. This was induced by the cooling effect of the fog and the associated smaller ventilation openings.
There are two standard techniques for scheduling irrigation of orchards: soil moisture monitoring and evaluation of evapotranspiration made with the use of standard pan or Penman-Montheich model. Limitations of these techniques are well known. Nowadays, the use of physiological indicators for assessing dynamics of plant water status has attracted attention of many growers and experts. The large-scale field tests of phytomonitoring technique and instrumentation were carried out in Israel in 2000. A few dozens phytomonitors were installed in apple, plum, peach, kiwi, mango, persimmon orchards and avocado, citrus, table grapes and banana plantations. Besides environmental factors, the trunk, shoot and fruit growth were subjects of monitoring. The phytomonitoring technique was used for fine-tuning irrigation scheduling according to two criteria: a good yield with less water. Encouraging results have been obtained in most cases. Many growers have reported substantial savings in water at due level of yield and quality.
Computers and Electronics in Agriculture j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c o m p a g a b s t r a c t This review covers developments in non-invasive techniques for quality analysis and inspection of spe-cialty crops, mainly fresh fruits and vegetables, over the past decade up to the year 2010. Presented and discussed in this review are advanced sensing technologies including computer vision, spectroscopy, X-rays, magnetic resonance, mechanical contact, chemical sensing, wireless sensor networks and radio-frequency identification sensors. The current status of different sensing systems is described in the context of commercial application. The review also discusses future research needs and potentials of these sensing technologies. Emphases are placed on those technologies that have been proven effective or have shown great potential for agro-food applications. Despite significant progress in the development of non-invasive techniques for quality assessment of fruits and vegetables, the pace for adoption of these technologies by the specialty crop industry has been slow.