Within-vineyard variability in grape quality and yield and its relationship to the vineyard environment

The pattern of spatial variation in several key productivity variables, vine characteristics and environmental parameters, was identified in a vineyard block in the Yarra Valley region of Victoria. The 3.4 ha block was characterised by changes in both elevation and aspect. Yield was measured using a harvester mounted yield monitor and quality assessments were made on 90 samples taken on a 15 m grid. An EM38 survey was done to assess overall soil variability while microclimate and soil temperature were measured using a network of micro loggers in the vineyard. Surface soil moisture (SSM) surveys were done regularly using a volumetric water content sensor at each of the sample locations. It was found that grape yield varied more than grape characteristics with CVs of 18.34% and 1.58-9.6%, respectively. Overall, high yielding sections of the block were found to lack maturity with low Baume and high acidity fruit. Pearson Correlations (r) were used to describe the relationships between variables. Yield, berry weight, bunch weight, titratable acidity (TA) and foliage density all showed strong positive correlations (r >0.5) with SSM at both budburst and veraison. Baume and pH, on the other hand, did not show a correlation with SSM but did show a strong positive correlation with overall daily mean air temperature. SSM was highly correlated (r >0.76) with the EM38 signature and negatively correlated with budburst across the block. The results from this investigation suggest that although soil characteristics such as soil moisture can dominate patterns of variability in yield and fruit composition, soil and air temperature still exert an important influence.