Effects of vineyard deficit irrigation on berry composition and yield during 2014 California drought

Abstract

The effect of deficit irrigation on berry composition, berry weight and yield was studied across 5 vineyards located in two regions exhibiting Mediterranean climate in California. The study used sap flow and pre-dawn leaf water potential (PDWP) to monitor the water status of the vines and trigger irrigation opportunities. Vineyard blocks were “split” and two irrigation regimens were imposed: traditional and experimental. Traditional treatment for each vineyard continued conventional methodologies used by growers at each site. Experimental sites used sap flow as the primary indication of irrigation timing while PDWP was used to confirm sap flow data. Fruit composition was monitored starting at veraison through to harvest, monitoring primary metabolites at all sites and secondary metabolites at participating sites. Variables monitored included: water applied, berry weight, tannin, total anthocyanins, yield, water deficit index, sugar concentration, pH and titratable acidity. Data from all sites was combined and correlations between all variables were determined. A regression analysis was also used to analyze the effects of the amount of water applied and water deficit index on yield components and berry composition. Simple data analysis shows the differences between water input in the traditional and experimental sites (30 – 100% water savings). Study outcomes were largely inconclusive and despite the strong correlations obtained between variables, they were often inconsistent with literature. Berry weight was found to have a moderately negative correlation with the amount of water applied and water deficit index. Tannin content was also found to have a negative relationship with the amount of water applied. Brix was found to be positively correlated with water applied and water deficit index. These inconsistent results may be due to factors such as different varieties, sites and management techniques being used across different producers. The absence of statistically robust results prevent us from drawing conclusions. Additional research is suggested to confirm this results in order to evaluate the viability of using the sap flow technique to manage deficit irrigation