Reflective materials for anthocyanin synthesis and colour enhancement of fruits: visualization, carbon footprint, sustainability and effects of soil contamination


To reduce plastic use to improve the red coloration of fruit, particularly under hail nets, three alternatives to white woven reflective mulch in every row were explored using ‘Braeburn Hillwell’ apple trees on ‘M.9’ under a grey hail net with uncovered grass alleyways as control. Good fruit colouring was achieved a) through substituting the white ground cover (Lumilys™) with aluminium foil (80% recycled), and b) through spreading the white woven ground cover every other row, which would reduce greenhouse gas (GHG) emissions by ca. 100 kg CO2eq ha-1 year-1. To simulate autumn gales, the effect of ground cover contamination with dry soil on light (VIS/NIR) reflection was measured a) in the laboratory by a spectrometer (500-1000 nm), b) in the orchard at Klein-Altendorf (50 °N) on a sunny day in August 2018 by a PAR (400700 nm) sensor 1 m above the ground cover and c) by a profilometer. Diffuse light reflection from clean Lumilys™ ranged from almost 100% at 500 nm to ca. 92% at 900 nm, but only from 30% at 500 nm to ca. 60% at 900 nm after strong contamination with 51 g soil m-2. Unexpectedly, light or moderate soil contamination (3-12 g soil m-2) increased diffuse PAR reflection by 11%, whereas strong soil contamination (51 g m-2) reduced the diffuse light reflection by ca. 25% when measured at a 45° angle 1 m above Lumilys™. The unexpected results of increasing diffuse light reflection after light to moderate soil contamination of the mulch can be explained by a ca. 30% increase in surface roughness (Sa) from ca. 22 µm (clean control) to ca. 28 µm (contaminated) shown by false colour images from a profilometer (Keyence). Overall, multiple uses in the same or several years, spreading in every other row or substituting it with another reflective material and continued (re-)use even after light to moderate contamination, could reduce plastic use and thereby contribute to more sustainable use of plastics in the orchard.