RADIATION TRANSMISSION THROUGH COLOURED SHADE NETTING AND PLASTICS AND ITS EFFECT ON EUCALYPTUS GRANDIS × E. NITENS HYBRID MINI-HEDGE SHOOT INTERNODE LENGTH, STEM DIAMETER AND LEAF AREA

D.L. Gilbert, I. Bertling, M.J. Savage
Quantity and spectral quality of radiation is important when growing plants under protection (tunnels) and particularly for vegetative propagation due to the varying effect of the radiation spectrum on plant morphology. Five coloured shade nets and two plastics were evaluated with regard to their transmission of radiation and alteration of spectral irradiance (300 to 1100 nm waveband) in autumn, winter and spring using a spectroradiometer. Transmissivity, total spectral irradiance, photosynthetically active radiation (PAR), photosynthetic photon flux density (PPFD), red to near infrared ratio (R:NIR) and blue to red ratios (B:R) were determined. Using an incandescent lamp in the laboratory, transmissivity for each shade net and plastic was compared with that for the propagation tunnel. The Aluminet× (silver), black shade nets and Patilite E× clear plastic transmitted radiation neutrally over the entire spectrum, while the blue, red and green shade net as well as Clarix E Blue× plastic altered the transmission of certain wavelengths. The R:NIR values for shade nets and plastics were significantly different over the seasons, but did not vary enough to affect the shoot internode length ranging from 1.13 to 1.22 in autumn to 1.05 to 1.16 in winter. Plants under the blue and green nets had the shortest internode length, while those under the Clarix E Blue× and red net had the longest, corresponding with results that Clarix E Blue× had the smallest R:NIR values and the blue shade net the largest. The average transmission percentage of PAR, using an incandescent lamp, in a laboratory gave more accurate measurements compared with the shading percentage given by the manufacturers. When the NIR was added to the PAR, the average transmission percentage increased for all shade nets and plastics, particularly those that exhibited photoselective spectra. Laboratory transmission measurements were generally much lower than those under field tunnel conditions. Manufacturers seem to base the shading factor percentages of nets and plastics on PAR, excluding NIR and wavelengths beyond. For photoselective materials these excluded wavelengths may skew the expected absolute transmission of radiation.
Gilbert, D.L., Bertling, I. and Savage, M.J. (2013). RADIATION TRANSMISSION THROUGH COLOURED SHADE NETTING AND PLASTICS AND ITS EFFECT ON EUCALYPTUS GRANDIS × E. NITENS HYBRID MINI-HEDGE SHOOT INTERNODE LENGTH, STEM DIAMETER AND LEAF AREA. Acta Hortic. 1007, 773-780
DOI: 10.17660/ActaHortic.2013.1007.91
https://doi.org/10.17660/ActaHortic.2013.1007.91
blue:red, propagation, red:near infrared, spectral irradiance, transmissivity
English

Acta Horticulturae