Mobile shading versus whitewashing: evaluation of the agronomic response of a tomato crop

The ambient temperature and evaporative demand in the Mediterranean greenhouses are excessively elevated during the high solar radiation season, which has harmful effects on growth and development of the crops, decreasing yield and quality of the products. The current cultivation structures have very poorly efficient natural ventilation systems, therefore making necessary the use of some additional cooling technique. The vast majority of growers turn to shading the greenhouse cover by means of whitening, a fix shading method that leads to considerable losses of the productive potential of the crop. The objective of the present study was to compare the yield response of a tomato crop ('Bigram') grown in coir substrate under two different greenhouse shading systems: traditional whitening (R) and mobile shading diffusive screen system (HS) located inside the greenhouse. The effect of these two different shading systems on the water use efficiency was also evaluated. At the end of the crop cycle, the incident and intercepted PAR were respectively 31.2 and 16.4% higher in the HS greenhouse. The crop grown under the mobile shading obtained an increase of 25% in the marketable yield in relation to the greenhouse with traditional whitening, which at the end of the evaluated period involved 2 more harvested trusses m^-2, caused by a shorter period of fruit growth and development. The mobile shading system proved to improve the climate in Mediterranean greenhouses and also the water use efficiency.