Above and below-ground environmental changes associated with the use of photoselective protective netting to reduce sunburn in apple

Abstract

Anti-hail (protective) netting was originally developed to protect horticultural crops from hail damage. Netting reduces the amount and modifies the light reaching the orchard canopy. It also has the potential to optimize conditions for canopy and fruit growth and mitigate abiotic stress as climate change leads to increased temperatures. This study measured the effect of different colors of netting on the above and below-ground environment and apple sunburn incidence in a 3-year-old 'Honeycrisp' apple orchard growing in an irrigated desert climate in comparison to a traditional uncovered control. Netting did not affect air temperature or relative humidity within the orchard canopy, but reduced wind speed by 40% compared to the uncovered control. Netting reduced soil temperature and improved soil moisture at 20 and 40 cm depths throughout the study period compared to the uncovered control. Amongst different colors of netting tested in this study, pearl and blue netting significantly reduced soil temperature compared to red netting. Netting also reduced photosynthetically active radiation (PAR) by approximately 20% and strongly reduced fruit surface temperature during hot periods. During full sunlight, differences in maximum fruit surface temperature between the uncovered control and the protective netting were 2.6 to 4.3°C under full sun conditions and reduced the incidence and severity of sunburn measured at harvest. As temperatures warm in the future, netting provides a viable option to mitigate some of the negative effects of excessive temperature and light on apple production in hot, dry growing regions.

Protective Netting Improves Leaf-level Photosynthetic Light Use Efficiency in ‘Honeycrisp’ Apple Under Heat Stress

“…Although there was no replication of netted and non-netted treatments, in our experiments, peak PPFD was %1470 mmol · m -2 · s -1 under blue PN compared with %1880 mmol · m -2 · s -1 for the uncovered control for the clear sky measurement days. This was consistent with data provided in Kalcsits et al (2017). Light saturation for photosynthesis in apple has been reported to be %700 to 800 mmol · m -2 · s -1 in 'Braeburn' (Tartachnyk and Blanke, 2004) and 800 mmol · m -2 · s -1 in 'Stayman', 'Red Prince Delicious', and 'Tengmu' cultivars (Campbell et al, 1992;Husen and Dequan 2002).…”

“…In our experiments, trees under blue photoselective PN demonstrated indicators of reduced light stress compared with the control despite consistent light intensity across the measurement days. The above-canopy ambient temperature was not different in the blue photoselective PN treatment irrespective of ambient temperature on the day of measurement, as also reported by Kalcsits et al (2017). Although still experiencing the same ambient temperature during the experiment as the control, trees under blue photoselective PN were exposed to lower light stress.…”

“…PN has been reported to reduce ambient temperature (Middleton and McWaters, 2002;Solomakhin and Blanke, 2010), but Arthurs et al (2013) found that 50% red, blue, and pearl PN increased ambient temperature. Kalcsits et al (2017) found no significant differences in ambient temperature under photoselective PN compared with an uncovered control. The inconsistent results obtained may be due to radiation shielding not being used with the temperature sensors in some studies.…”

“…For example, ambient temperature readings from a sensor that is exposed to solar radiation have been reported to be 4 to 6°C higher than ambient temperature readings from inside a Stevenson Screen (Middleton and McWaters, 2002). Photoselective PN reduced soil temperature under Washington State conditions at depths of 20 and 40 cm (Kalcsits et al, 2017). PN also has been reported to lower the wind speed (Arthurs et al, 2013;Kalcsits et al, 2017;Middleton and McWaters 2002) and increase relative humidity (Middleton and McWaters, 2002;Solomakhin and Blanke, 2010).…”

“…Leaves exposed to full sunlight can heat up substantially above ambient temperature (Sharkey, 2005). The leaf temperature of 'Honeycrisp' apple was reported to be 36.2°C when ambient temperature was 28.8°C (Kalcsits et al, 2017). Enzymes involved in chlorophyll biosynthesis are affected by heat stress (Tewari and Tripathy, 1998).…”