Determination of the spectral properties of several greenhouse cover materials and evaluation of specific parameters related to plant response

The spectral radiometric properties of various greenhouse cover materials (glass and seven plastic films) were measured in the laboratory using a spectroradiometer equipped with an integrating sphere. For the fluorescent material, the transmission was determined outdoors, under natural daylight. From the transmission curves, the parameters related to the photosynthetically active radiation (PAR) transmission (tau(PAR), 400-700 nm) and the ratio zeta (red/far red irradiance) were calculated. It was observed that zeta was higher for the fluorescent material than for the classical films and lower for the shading coloured film, but their PAR transmissions were lower. The effective photosynthetic transmission (eta) and quantum transmission (E) were determined by weighting the spectral transmission curves with, respectively, the photosynthetic and quantum yield efficiencies of an average plant. Only small differences were found between values of eta and E for classical plastic materials and glass, but significant differences for the fluorescent and shading coloured films. It can be concluded from these results that the accurate determination of some specific parameters as zeta, eta or E for selective or fluorescent materials is necessary in order to assess their influence on plant growth and development under greenhouse conditions. (C) 1998 Silsoe Research Institute.