Effect of Air Velocity and High Relative Humidity on Growth and Water Use Effi ciency of Cucumber in a Closed Greenhouse Environmental Control System

Abstract

To develop an effective method for improving water use efficiency in a closed greenhouse environmental control system, we investigated the effects of air velocity on the growth and water use efficiency of cucumber seedlings under high relative humidity. Seedlings in closed plastic chambers were exposed to one of three air velocities in closed plastic chambers: 0 m s^-1, 0.24 m s^-1, or 0.66 m s^-1. Dry weights of the cucumber seedlings in the 0.24 m s^-1 and in 0.66 m s^-1 air velocity treatments were higher than that of seedlings in the 0 m s^-1 treatment. Seedlings subjected to an air velocity of 0.24 m s^-1 was the highest among the treatments, at an average of RH 92.1 %. In addition, seedlings exposed to 0.24 m s^-1 and 0.66 m s^-1 winds had higher water use efficiencies than seedlings in the 0 m s^-1 treatment. These results indicate that in a closed greenhouse environmental control system, controlling air velocity at high relative humidity makes it possible to increase the photosynthetic rate of seedlings while minimizing increases in water uptake.