Effect of crushed glass, used as a reflective mulch, on Pinot noir performance

Abstract

Research conducted at Lincoln University, New Zealand, evaluated an alternative use for recycled glass in its crushed form as a mulch under grapevines. The trial comprised four treatments: clear glass, brown glass, mixed glass (which is primarily green and brown) and undisturbed soil as a control, with four replicates in a randomised block design. The vine material was twelve year-old Pinot noir 777 on 3309 rootstock. Radiation reflected back up into the fruiting zone was quantified using a Bentham spectroradiometer under clear and sunny field conditions. Reflection from the mulches was also measured under controlled conditions. The results showed that clear glass reflected the highest amount of radiation in all the spectral ranges evaluated. UV-B radiation reflected by clear glass was double that reflected by the control. UV-A reflected by clear glass was about seven times more than that of the undisturbed soil treatment. Readings for PAR were almost five times larger than the control and, for infra-red (IR), this difference was twice as much as for the control. PAR was also divided in different “colours”, with clear glass being the most reflective treatment in all PAR ranges. Similar data were obtained from the evaluation of the mulches under controlled conditions. However, the extra amounts of radiation reflected by the mulches did not have any effect on havest parameters: number of clusters, cluster weight, potential crop, ºBrix, pH or TA.

Aromatic profiles of the juice obtained from the grapes of this trial were evaluated using GC-O analysis. The panellist identified seven aroma descriptors from the samples: cut grass, mushroom, fresh peas, violet, cooked potato, rose and blackberry. Despite more aromas being detected, these were the ones most frequently sniffed by the panellist. The descriptors corresponded only to an association between panellist’s perception and a known aroma. The use of reflective mulches showed an influence on the aromatic profile of the grape. Clear glass decreased the intensity of the cooked potato-like aroma. This treatment also enhanced the aromas described as roses and blackberry when sniffed by the panellist. GC-MS and a mix of standards were used to determine the compounds related to each of the aromas described by the panellist. Hexanal was reported as the compound related to the aroma described as cut grass, and 1-hexanol was related to the aroma described as fresh peas. The rest of the descriptors were only tentatively identified. To do that, the retention time of each descriptor was compared with an alkane mix of standards and information registered in the literature. For mushroom aroma, 2-octanone was described as the most possible compound related to this aroma in the samples analysed. The aroma described as violet was associated to four different compounds: (Z)-linalool oxide, (E)-linalool oxide, nerol oxide and linalool oxide. The cooked potato-like aroma was related to methional, which was described for the first time in this experiment on Pinot noir juice. Linalool was associated with the aroma described as rose by the panellist, and β-ionone was related with the blackberry-like aroma.