THE EFFECT OF SHADING NETS ON GREENHOUSE MICROCLIMATE

A major problem confronting Mediterranean greenhouse horticulture is the excess of heat during summer. One of the methods to alleviate the heat load is shading with nets. Shading nets can either be fixed or mobile. They can be external (above the greenhouse) or internal (inside the greenhouse above the crop). Experiments were carried out in a greenhouse in which a tomato crop was grown. The greenhouse was divided into two separated compartments of three spans each. In one compartment a 30% shading net was applied above the greenhouse, on top of the polyethylene cover, while in the other compartment it was stretched horizontally inside the compartment, at gutter height. Solar radiation outside and inside each compartment and light intensity above the crop and at ground level, and air temperature and humidity, in each compartment, were continuously measured over the growing period. The results show that in well ventilated houses net position does not significantly affect the values of the measured parameters and hence has no significant effect on greenhouse microclimate when the shading percentage is 30% or lower.