Microclimate and tree physiology of 'Nadorcott' mandarin are affected by shade netting

G.H. Barry, D.M. Prins, O.P.J. Stander, P.J.R. Cronjé
The use of shade netting to change light quality and quantity is primarily focused on increasing return on investment by reducing the occurrence of damage to fruit. After installing 20% white permanent shade netting over a 'Nadorcott' mandarin orchard planted in 2012 in Citrusdal, Western Cape Province, South Africa, the expected change to the microclimate which in turn could affect a tree's physiology was recorded during 2016 and 2017 in both netted and open situations. Hourly logging of solar radiation, air and soil temperatures, relative humidity, soil water content and wind speed were conducted, in addition to monthly measurements of photo-assimilation, stomatal conductance and leaf gas exchange. Solar radiation was reduced by ~17% under shade netting, and mean and maximum temperatures were reduced on top of the canopy, whereas minimum temperature was higher. However, temperature within the canopy (1.5 m from soil level) was higher under shade netting and this led to a significant increase in effective heat units as well as relative humidity under the netting which in turn lowered the VPD. Average soil temperature was higher under shade netting resulting from less diurnal fluctuations between minimum and maximum temperatures. Soil water content was increased by ~17% furthermore the average and maximum wind speed was reduced under shade netting which acted as an artificial windbreak. Cumulatively, the shade netting had a positive effect on carbon assimilation during the summer months coinciding with phase II of fruit growth. To conclude, 20% white shade netting affected the microclimate of a 'Nadorcott' mandarin orchard in Citrusdal and thereby positively affected the trees' physiology by allowing an increase in photosynthesis.
Barry, G.H., Prins, D.M., Stander, O.P.J. and Cronjé, P.J.R. (2020). Microclimate and tree physiology of 'Nadorcott' mandarin are affected by shade netting. Acta Hortic. 1268, 271-278
DOI: 10.17660/ActaHortic.2020.1268.35
photosyntheses, carbohydrates, irradiation, wind speed, vapor pressure deficit, Citrus reticulata 'Blanco'

Acta Horticulturae