Shading

Although photosynthesis rates typically increase with higher irradiance, too high irradiances can damage the photosynthetic system, mainly when other stresses such as extreme temperature or water stress occur (Jones, 2014). In these cases, shading can be helpful to moderate the light intensity (Photo 4.18). Shading affects the energy available for heating and evaporation, and it may lower soil temperatures and reduce water evapotranspiration, maintaining higher soil moisture levels. The lower evaporative demand under shade allows plants to increase stomatal conductance and CO₂ assimilation (Mahmood et al., 2018).

 

Shade nets can also protect against frosts and chilling effects by capturing the long-wave radiation that would have escaped easily in the open air (Stigter, 1984b). Shading also increases the absolute air humidity, decreasing the evaporative demand. Mahmood et al. (2018) found that shading screens increased relative humidity by 2-21%, reduced air temperature by 2.3-2.5°C, and decreased evapotranspiration by 17.4-50%. Several studies also showed that shading screens could help reduce the vulnerability of hail and wind damage (Ilić et al., 2015). Tanny & Cohen (2003) found that a shade net reduced the wind speed by about 40% compared to an unshaded site. It should be considered that too little light intensity can decrease crops’ production if the crop is not getting enough light for the photosynthesis process (Rosenberg, 1983). Shading is thus helpful to facilitate the growth of shade-tolerant crops or where light intensity is excessive.