Alternatives to reflective mulch cloth (Extenday™) for apple under hail net?

Abstract

Fruit grown under hail net often suffer from lesser quality, lack of red colouration, insufficient fruit firmness viz storability and less sugar viz taste. Reflective white woven mulch cloth Extenday™ can overcome these shortcomings by improving light utilisation in the orchard, if spread 5–6 weeks prior to anticipated harvest on the grass of the alleys between the tree rows. The objective of the present work was to examine alternatives such as sustainable, organic materials including straw, lime and biodegradable white paint using 7-year-old cv. ‘Jonagold’ apple trees under a white hail net in Klein-Altendorf Research Centre near Bonn, Germany in August 2005. Uncovered grass strips served as control with a constant 6.6% light (PAR) reflection at 1.5 m height. When freshly applied, white paint initially reflected up to 8%, while fresh wheat straw reflected 13.6% light (PAR) commensurate to the reflective cloth Extenday™ with 13.9%, equivalent to a 2.1-fold increase in light reflection relative to the uncovered grassed control. No differences in ripening and starch breakdown were observed in the apple fruits, but reflective mulch improved their sugar content, and hence taste, by ca. 8% from 13.5% sugar in the control (uncovered grass alleys) to 14.6% sugar, without affecting the fruit size. The reflective mulch increased the percentage of class I fruit with >25% colouration by 8.3% (from 47.6 to 55.9%) under hail net in the grading relative to the control (grass alleys), resulting in financial gross or net gains of €870 or 530 ha −1. The apparent discrepancy between the large initial light reflection of the straw, and paint to a lesser extent, but poor fruit quality 6–7 weeks later at harvest may be explained by the grass, which eventually penetrated the straw over time and white paint being washed off by precipitation in the autumn, whereas the grass maintained its optical properties, indicating no organic alternative to the reflective white, woven cloth.