干旱区生态环境知识资源中心

The use of screens and screenhouses is constantly increasing, especially in arid and semi-arid regions where their use is environmentally sound. This is due to several reasons: (i) the relatively low initial and maintenance costs; (ii) saving irrigation water - a crucial environmental issue; (iii) improved yield quality; (iv) reduction in pesticide application by using high mesh screens. Our research group has been studying the microclimate, crop water use and water use efficiency of crops under screens and in screenhouses. This paper will review major findings of these studies. In Israel, much of the banana cultivation has moved inside screenhouses in order to save water and improve fruit quality. In the Jordan Valley water savings can reach 20-30% with the same and even better yield. Thus, water use efficiency is increased. Measurements and modelling have demonstrated that in this region the major factors contributing to evapotranspiration reduction under summer conditions are radiation and wind speed reduction. Pepper is mainly grown in screenhouses with high-mesh insect-proof screens. These screens are efficient in excluding the insects but they inhibit ventilation and reduce incoming radiation. Measurements have shown a reduction of about 50-70% in ventilation rate, and about 50% reduction in crop water use, as compared to estimated values for an open pepper field. The reduction in turbulent transport of mass and momentum was demonstrated through the study of aerodynamic properties of boundary layers along screens. These studies showed reduced friction velocities and roughness lengths above a covered citrus orchard. These findings support the observed reduction in evapotranspiration from covered crops.