Evaluation of plastic windbreak and glasshouse shading (Netlon) in Canterbury, New Zealand

Abstract

Abstract At Lincoln, New Zealand, the influence of Netlon plastic windbreak on wind reduction, wind turbulence, and evaporation, and of Netlon plastic shading on glasshouse humidity, temperature, light, and evaporation was assessed in early spring. A single layer of windbreak effected a maximum smooth, non-turbulent reduction of wind speed of 40% at 6H on the lee side (H = height of windbreak), and at least 20% reduction of open wind speed extending \s~ 20H. Evaporation was reduced by a max. of 30% and by at least 20% from 3 to 10H. A folded (i.e. double) layer reduced wind by a max. of 65% at 6H, and by at least 20% extending \s~ 19H, with very little turbulence; evaporation was reduced by a max. of 40% and by at least 20% over 15H from the windbreak. Glasshouse shading reduced luminosity by 40% and free-water evaporation by 25-30%, and lowered maximum daytime temperature by up to 6°p compared to an unshaded glasshouse; night minimum temperature was unaffected. Relative humidity was increased slightly both day and night, the daily amplitude being similar to that in the unshaded house.