Light spectrum modifications under photo-selective hail-nets

The hail-nets in fruit orchards can influence several environmental factors with specific modification of metabolism and production of plants. Aim of present work was to study the sunlight spectrum modification under six photo-selective plastic hail-nets (yellow, fluo, pearl, red, blue and grey), progressively wide spreading in fruit orchards after their introduction in early 2000, in comparison with the most largely used black and neutral nets. Light spectra under the nets were measured 5 times in a fixed structure, with the nets almost perpendicular to solar light, using an array spectrometer. The spectra were measured between 320 nm and 800 nm, cumulating the irradiance in 40 nm intervals, in clear sunny days of September. Black net reduced irradiance more than all other nets, while neutral net the less. Neutral, grey, black nets induced a spectrum like solar light, but with an increasing shadow effect of 7%, 20%, 24%, respectively. The photo-selective nets induced an intermediate level of shadow (21% blue, 21% red, 18% yellow, 15% fluo and 13% pearl) but specific light spectra. Blue net reduced irradiance in the interval 600-720 nm more than all other photo-selective nets. Yellow and fluo nets reduced the irradiance more in the interval 400 – 520 nm, while red nets between 400-600 nm. The irradiance in the interval 320-400 nm (Ultra-Violet A) was reduced between 4 and 6 W/m2 by all the nets (photo-selective and black), except for neutral net, which reduced less than 2 W/m2 in the same interval. Black net reduced the irradiance 14 W/m2 in the interval 720 and 800 nm, more than all other colored nets, which ranged between 6 and 10 W/m2. Pearl and neutral nets reduced the less (4 W/m2). Red : far red ratio was not significantly modified by any of the photo-selective nets in comparison to that of sun light (1.23).