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For investigation of the relationship between plant growth and environmental factors in a plant factory, an experimental plant factory has been built and some experiments have been carried out. Leaf lettuce was grown in a hydroponic system under artificial light condition. Arial environment such as air temperature, humidity and CO2 concentration were controlled. Root environment such as EC and pH were monitored and controlled by a microcomputer.In the first experiment, EC level was maintained at a constant set-point and the difference between the set-point and the actual value was summed up when the latter value was corrected. Transpiration was also calculated from the water depression in the tank. Then it was summed up through the growing period.Following results were obtained:(1) The EC decrement showed high correlation with the transpiration, regardless of light intensity and (2) the transpiration rate per EC decrement decreased as the EC of nutrient solution became higher.In the second experiment, the effects of light intensity, lighting cycle and EC of nutrient solution on tipburn injury were examined.Following results were obtained: (3) The tipburn occurrence became later under the conditions that the EC was low and the duration of a lighting cycle was short and (4) the tipburn occurrence became later under the conditions that the light intensity was low and the duration of a lighting cycle was short.Effect of the duration of a lighting cycle on the tipburn occurrence showed larger as the light intensity increased. From the results of Tibbitts et al (1985), it is, therefore, considered that the pressure of laticifer or the Ca concentration in the wall of laticifer increases with the increase of the duration of lighting cycle and this could cause the tipburn.

Effect of EC of nutrient solution and light condition on transpiration and tipburn injury of lettuce in a plant factory.