Simulating Growth and Development of Tomato Crop

Crop models are powerful tools to test hypotheses, synthesize and convey knowledge, describe and understand complex systems and compare different scenarios. Models may be used for prediction and planning of production, in decision support systems and control of the greenhouse climate, water supply and nutrient supply. The mechanistic simulation of tomato crop growth and development is described in this paper. The main processes determining yield, growth, development and water and nutrient uptake of a tomato crop are discussed in relation to growth conditions and crop management. Organ initiation is simulated as a function of temperature. Simulation of leaf area expansion is also based on temperature, unless a maximum specific leaf area is reached. Leaf area is an important determinant for the light interception of the canopy. Radiation shows exponential extinction with depth in the canopy. For leaf photosynthesis several models are available. Transpiration is calculated according to the Penman-Monteith approach. Net assimilate production is calculated as the difference between canopy gross photosynthesis and maintenance respiration. The net assimilate production is used for growth of the different plant organs and growth respiration. Partitioning of assimilates among plant organs is simulated based on the relative sink strengths of the organs. The simulation of plant-nutrient relationships starts with the calculation of the demanded concentrations of different macronutrients for each plant organ with the demand depending on the ontogenetic stage of the organ. Subsequently, the demanded nutrient uptake is calculated from these demanded concentrations and dry weight of the organs. When there is no limitation in the availability at the root surface, the actual uptake will equal the demanded uptake. When the root system cannot fulfil the demand, uptake is less, plant nutrient concentration drops and crop production might be reduced. It is concluded that mechanistic crop models accurately simulate yield, growth, development and water and nutrient relations of greenhouse grown tomato in different climate zone

Optimal greenhouse design should take into account optimal climate management

The objective of this paper is to demonstrate that optimal greenhouse design must account for (and be combined to) optimal climate management. We prove this by showing that different strategies and set-points to control the greenhouse ventilators result in different ¿optimal sets¿ of design parameters. We determined these optimal sets for a passive greenhouse in Almería, Spain where tomatoes were grown. The greenhouse design parameters investigated in this research were: 1) the transmission of the cover for photosynthetically active radiation (PAR), 2) the transmission of near infrared (NIR) radiation and 3) the emission coefficient for longwave radiation of the cover. Six optimal sets of design parameters were determined by maximising the marginal revenues (crop yield minus costs of design parameters), under given climate conditions, and for different ventilation control strategies. Each ventilation control strategy had different set-points for the air temperature and carbon dioxide concen¬tration to control the greenhouse ventilators. To solve this optimization problem we used a dynamic crop-greenhouse model and an optimization algorithm. The model described the combined influence of the relevant design parameters, outdoor climate and ventilation control upon economic crop yield, through their effect on indoor climate. The yearly costs of the design parameters were empirically derived from prices, physical properties and lifespan of a number of greenhouse cover materials. Results showed that indeed for different strategies and set-points to control the green¬house ventilators different ¿optimal sets¿ of design parameters and marginal revenues were obtained. For example, the difference between the highest optimal NIR trans¬mission 1.00 and the lowest optimal NIR transmission 0.40 was 60%, while the highest marginal revenues 16.94 ¿m-2 differed 18,7% with the lowest marginal revenues of 13.77 ¿ m-2. Additionally, it was found that the cover design parameters were time dependent. In conclusion, only a combined optimal control and design approach that takes into account the best climate control strategy and the time dependency of the design parameters will ensure optimal design parameters and maximum marginal revenues

Modellering ruimtelijke lichtverdeling in gewassen: Opbouw en toepassing van een 3D model voor kas en gewas

Een 3D model voor lichtverdeling in kasgewassen is ontwikkeld om de meest efficiënte plaatsing van lampen (SONT, LED) te berekenen om hiermee op groeilicht en energie te kunnen besparen. Het onderzoek, in het kader van het programma Kas als Energiebron en gefinancierd door Productschap Tuinbouw en Ministerie van ELI, behelsde de bouw en test van het model, dat rekening houdt met lampposities en -eigenschappen, bladstanden en rijstructuur. De lichtabsorptie en gewasfotosynthese voor een ingevoerd lichtplan wordt gesimuleerd. In het rapport zijn een reeks kansrijke belichtingsscenario’s doorgerekend voor een representatieve gewasstructuur voor tomaat en roos. Het resultaat bleek sterk afhankelijk van padbreedte en aantal bladeren, maar minder van bladvorm en bladhoek. De belichting wordt efficiënter bij gerichtere plantbelichting door aanpassing van de lampreflector, gebruik van tussenbelichting en schermreflectie. Het lichtverlies naar vloer en kasdek worden hiermee gereduceerd. Voor vragen uit de sector is het 3D model nu op verzoek inzetbaar

De gemiddeld jaarlijkse waterbalans van bos-, heide- en graslandvegetaties

De gemiddeld jaarlijkse waterbalans van een aantal combinaties van bos- en heidesystemen op zandgronden is berekend met het simulatiemodel SWATRE. Bij bos is daarbij onderscheid gemaakt in een 3-tal bostypen: douglas, grove den en eik. Ook is gekeken naar een aantal combinaties van grasland met natte zandgronden en veengronden, alsmede een aantal kale zandgronden. Het totale aantal onderscheiden zandgronden is 14, terwijl het totale aantal doorgerekende combinaties 58 bedraag