Influence of mobile shading on yield, crop transpiration and water use efficiency

Horticultural cultivation in Mediterranean greenhouses requires the implementation of refrigeration systems to avoid stress situations, particularly under spring-summer conditions. Mobile shading, as a climatic conditioning system, provides reductions in greenhouse temperature and evaporative demand under daytime periods of high radiation. Two experiments were carried out to evaluate the effect of an external mobile shade on the transpiration and water use efficiency of tomato and cucumber crops when irrigation water of low and moderate salinity was used. The mobile shading improved the quality of tomato and increased marketable yield of cucumber, moreover it reduced crop transpiration and thus water uptake, and improved remarkably water use efficiency: 47 and 62% for the tomato and cucumber crops, respectively. If compared with good quality water, the use of irrigation water of moderate salinity (5 dS m(-1) for tomato and 3.6 dS m(-1) for cucumber) reduced water use efficiency of the tomato crop and no effect was observed on the cucumber crop. Selective shading seems to be an interesting cooling method in climates with high evaporative demand, particularly in those areas where water is a scarce resource.