Microclimate and evapotranspiration of crops covered by agricultural screens: A review

The use of porous screens to cover agricultural crops is constantly increasing. Screens are mainly used to reduce high radiation loads and wind speed, to protect the crop from hail storms and to minimise the invasion of insects thus allowing a significant reduction in pesticide application. Since screens impede the exchange rate of radiation, mass, heat and momentum between the crop and the atmosphere they modify the crop microclimate and its water requirements. The increased use of screens by growers has triggered the expansion of research on the effects of various screens and screenhouses on microclimate and crop evapotranspiration, as well as on produce quality and quantity. Although research on screenhouse microclimate can be traced back to the beginning of the 20th century, only during the past few decades has a much better understanding of the screenhouse environment been achieved. This paper reviews past research and recent advances regarding microclimate and evapotranspiration of crops under screens and in screenhouses. It covers the issues of radiation, air velocity, ventilation, turbulence, temperature, humidity, evapotranspiration and water use efficiency. The review shows that although screens reduce the transmission of total radiant energy, the effect on air temperature is complex, and depends on additional factors. Future research should focus on modelling the screenhouse-crop system under realistic conditions, using advanced simulation tools. High quality data sets from field studies will be needed to develop and validate such models.

► Screens decrease radiation, air velocity and ventilation rate of covered crops.
► Several turbulence characteristics are almost unchanged from their open field values.
► The effect of screens on air temperature depends on several factors.
► Under certain conditions screens may increase plants' water use efficiency.