Effects of air current speeds on the microclimate of plug stand under artificial lighting

Experiment was performed in a newly developed wind tunnel with light system (Kim et al, 1996) to investigate the effects of air current speed on the microclimates above and inside the stand of plug seedlings (plugs). Objective of this study was to collect basic data for a large-scale plug production under artificial light in a semi-closed ecological system. Maximum air temperature appeared near the top of the plug stand. Difference in relative humidity (DRH) to the relative humidity at the inlet of the main air flow conditioner inside and above the plug stand decreased with increasing the air current speed. DRH inside a stand of plugs was 5-10 % lower at air current speed of 0.9 m s ^-1 than that of 0.3 m s^-1. DRH inside a stand of plugs was 2.8-6.5 % higher at LAI of 2.6 than that at LAI of 0.5. Difference in vapour pressure deficit (DVPD) to the vapour pressure deficit at the inlet of the main air flow conditioner inside and above the plug stand increased with increasing the height above the medium surface. DVPD inside the plug stand was 0.3-0.4 kPa higher at the air current speed of 0.9 m s^-1 than that at the air current speed of 0.3 m^-1. Results for the effects of air current speed on relative humidity and vapour pressure deficit indicated that the microclimates above and inside the plug stand at the rear region in plug trays were slightly unfavorable compared to those at middle region. Concentration of CO₂ near the top of a stand of plugs was 8-12 μmol mol ^-1 lower than that above a stand of plugs. The concentration of CO₂ at the rear region was 3-4 μmol mol^-1 lower than that at the middle region. CO₂ enrichment would be effective to the uniform growth of plug seedlings growing at controlled air current speed under artificial light in a semi-closed ecological system.