Spectral distribution of light under different structures and cover materials employed in Mediterranean greenhouses

Abstract

Light quality is related with the intensity of photosynthetic active radiation (PAR) received by the crop, but the spectral distribution of light can also influence the plant development (photomorphogenesis) and some plant physiologists have defined the concept of morphogenetically active radiation (MAR). In Mediterranean areas, ornamental crops, especially in summer conditions, are cultivated under different structural typologies and, also, in the open air. The aim of this work is to characterize and evaluate the quality of the radiation recording the different bands of the light spectrum affecting crop production, offered by different structures and cover materials employed in Mediterranean greenhouses. The spectrum regions studied were the following: ultraviolet UV (300-400 nm), blue B (400-500 nm), red R (600-700 nm), far red FR (700-800 nm), PAR (400-700 nm), near infrared NIR (700-1100 nm) and Global (GR) (300-1100 nm). The results show how structures modify the global radiation transmission uniformly through the spectrum, apart from the case of the UV band where the “Parral” greenhouse (PG) transmission is lower. The use of aluminised screen reduces the global radiation in the greenhouse, but this reduction is not homogeneous in the different bands where UV and B bands present the highest reduction. The ratios PAR/NIR; B/R; B/FR and R/FR were higher without aluminised screen. The use of anti-pest mesh supposes a loss of radiation received by the crop and it is more noticeable in the UV and B bands with around 30% of reduction.