Investigations into drip irrigation and leaf water potential with the grapevine varieties 'Riesling' and 'Syrah'

Investigations into drip irrigation and leaf water potential with the grapevine varieties 'Riesling' and 'Syrah'. The influence of drip irrigation (75 1 and 160 l per vine, resp.; seven application dates from bunch closing to veraison) was investigated with the grape varieties 'Riesling'(over a period of two years) and 'Syrah' (over a period of three years) with three experimental variants. Irrigation caused an increase of cluster density 177 the rather dry summers of 2006 and 2007, but not in the wet summer of 2008. In 2007 leaf water potential was proportional to the amounts of gated water. At BBCH 83 the leaf water potential from highly irrigated vines (160 litres per plant) reached a mean value of -0,39 MPa. Less irrigation (75 litres per plant) showed a mean value of -0,59 MPa and non-irrigated vines a mean value of -0, 73 MPa. In 2008, however, there were no significant differences in leaf water potential (-0,33 to 0.42 All-a) between the different variants at BBCH 79. In tendency a positive Influence of irrigation on the must density and the potassium content in the must was noticed in the grapes of 'Riesling' in 2007, the lowest values in all analysed parameters (cluster weight, berry weight, must weight, contents of potassium, Magnesium and nitrogen) were found with the non-irrigated variant of 'Riesling'. In 2008 no differences in the parameters cluster weight, berry weight, must weight, titratable acidity and nitrogen content could be registered with 'Riesling'. With 'Syrah' no significant differences between the variants could be noticed in 2006. 177 2007 tendencies towards lower cluster weight, higher must density, lower potassium contents and lower nitrogen contents in the must were found withthe non-irrigated 'Syrah' vines. In 2008 differences in cluster weight, berry weight and must density were found, but without statistic significance Lower potassium contents and nitrogen contents in the must were measured in tendency with the non-irrigated vines.