Influence of soil covering, plastic ageing and roof whitening on climate and tomato crop response in an unheated plastic Mediterranean greenhouse

In order to access the influence of soil covering, plastic ageing and roof whitening in a Spring/Summer tomato crop on permanently ventilated unheated plastic covered greenhouses in Portugal, several micro-meteorological measurements were made with soil covered with a double face white/black PE firm and with roof whitening during the hot end of the production cycle. These measurements were compared with a similar greenhouse with a new plastic cover, without soil covering and without roof whitening. Comparisons were based on greenhouse air and soil temperatures, inside global radiation, relative humidity and other indicators as the relation between plant leaf and air temperatures. Crop response analysis was based on fruit setting and fruit fresh weight production curves. Film ageing resulted in an average radiation transmission drop of 9% on global radiation and of 7% on PAR, relative to outside radiation levels. Soil covering lowered the frequency of periods with leaf temperatures equal or higher than air temperatures and also induced about one week of earliness on fruit set and harvest. Whitening of the roof led to a radiation transmission reduction of about 50%. This significantly reduced the frequency of periods with air temperatures above 30 degreesC. Whitening also reduced over 80% the frequency of periods with leaf temperatures equal or higher than air temperatures.