Reflective mulch effects on the grapevine environment, Pinot noir vine performance, and juice and wine characteristics

Abstract

Reflective mulches were applied in a cool climate vineyard in Canterbury, New Zealand. Materials used were waste products: mussel shells (MS) and green (GG) and clear (CG) recycled crushed glass. A control of bare soil was also included. MS and CG were light coloured while GG and CON were dark. Treatments were applied randomly within each of three replicates. Soil parameters tested were temperature, moisture, microbial biomass carbon, dehydrogenase enzyme activity and nutrient levels. Also investigated were canopy temperature and radiation reflected from each treatment. Vine parameters included nutrient levels, photosynthesis, leaf greenness, fruit components and pruning weights. Juice and wine parameters included wine colour, phenolic concentration and acid composition. A blind tasting was held and gas chromatography-olfactory (GC-O) was used to analyse aroma profiles of wine and juice. Mulches affected various soil parameters. MS buffered soil temperature and all mulches increased soil water retention especially MS. MS had higher microbial biomass carbon than glass. Soil pH levels increased under MS while sodium levels were highest for GG. Higher levels of vine canopy boron, copper, potassium, molybdenum, phosphorous and sulphur were found for mulches. No differences were noted for vine gas exchange although differences were found for related parameters between mulches and CON. Cluster number and fruit weight were higher for light compared to dark treatments and pruning weights were highest for light and mulched treatments. All mulches reflected solar radiation into the canopy. No differences were found for canopy temperature at any stage during the growing season however differences for light parameters were highly significant. Part of the ultra violet spectrum (300 - 400 nm), photosynthetically active radiation (380 – 760 nm) and red to far red ratios (660:730 nm) were all higher for light compared to dark treatments. Analysis of wine attributes such as colour, phenolics, acids and aroma suggested a treatment effect on the wine. The tasting also highlighted, that reflective mulches could be used to alter wine flavour, aroma and mouthfeel. Differences in juice aromas measured by GC-O were reported slightly differently by each panellist who detected them, but significant results were found within each data set. The first panellist recorded more differences between mulch treatments and CON with higher results in most cases for CON regardless of aroma type. For the second panellist results were more varied with significant results for different comparisons and a range of aromas. Reflective mulches directly affected environmental and vine performance parameters. They could be applied in the vineyard to optimise the distribution of radiation, improve vine health and productivity. These effects have had a subsequent impact on the fruit and wine produced. It is clear from this trial that mulches had impacted on juice and the research forms a basis for future work. Ultimately the mulches offer the possibility to manipulate aromas, which could be a useful tool for winemakers in cool climates who seek to make consistently distinctive wines in variable conditions.