Effects of grennhouse lime shading on filtering the solar radiation

Protecting crops under a greenhouse allows their optimal management all over the year. Mostly during summer, in order to limit the indoor temperature and create suitable internal growing conditions, a common traditional solution is whitening the external side of the cladding material with slaked lime (calcium hydroxide– Ca(OH)2). The benefits of whitewashing reported in the literature confirm that it has positive effects both on the microclimate and on the development of crops. This paper shows the results of a research, performed by using spectrophotometers in the Laboratory for Testing Materials of the University of Basilicata (Italy), aimed to analyse different types of calcium hydroxide solutions. The analysis verified the variation of radiometric properties and shading effect. The whitening concentration was a fixed dose of simple calcium hydroxide, diluted in two different water concentrations, then painted on an EVAC plastic film. Moreover, an un-painted transparent EVAC plastic film was considered as a reference. The radiometric measurements on the samples were carried out to measure transmittance, reflectance and absorbance on all wavelengths of the Photosynthetically Active Radiation (PAR). The results have given information on the effect of different dilutions of slaked lime on the selective filtering of the solar radiation. These conclusions may be useful to compare similar results with more recent solutions for greenhouse shading, such as the use of plastic nets.