Deliverable 5. Multivariate analysis of climatic and physiological factors affecting transpiration in relation to water or osmotic stress on greenhouse crops. (ARO-ISWES)
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Deliverable 5 presents a procedure for evaluating the effect of independently varying external climatic factors on the transpiration of greenhouse crops under summer conditions. It predicts the crop canopy temperature, air temperature and humidity inside the greenhouse. It uses greenhouse construction characteristics as input parameters, and takes into consideration ventilation rate and plant water stress. The analysis also examines the effect of evaporative cooling for a greenhouse fitted with an evaporative wet pad. For any given cooling efficiency, the procedure evaluates the temperature and humidity of the air leaving the wet pad and evaporation rate from the wet pad.
Irrigation is always the water provider of plants grown in greenhouses. Proper management of the water input requires knowledge of the water consumption by plant transpiration. In modern greenhouses, nutrients are added to the irrigation water. Through this practice, water application entails also nutrient application associating water and mineral dosage. In the case of closed-loop irrigation systems, transpiration concentrates non-nutrient ions like Na+ and Cl- in the irrigation solution. The raised osmotic potential of the root medium or by toxicity of the ions may harm the crop. Therefore, transpiration is an essential process determining the hydraulic and chemical environment of crop grown on artificial substrates in closed-loop systems. The purpose of this deliverable is to establish the relations between climatic, physiological factors and transpiration. A special effort is made to identify independent variables, and parameterize climate control operations to quantify their effect on transpiration and the internal microclimate in the greenhouse. An EXCEL workbook presents the results of the analysis in an interactive multivariate format that allows the user to manipulate the relevant independent inputs and the climate control operations like ventilation, shading and evaporative wet pad.