Experiments to modify grape juice potassium content and wine quality on granite derived soils near Paardenberg

[摘要] High potassium content in grape juice and wine are associated with lowquality red wine in warm wine producing countries. In an attempt to reducethe potassium content of juice, must and wine, a field experiment was laid outon the farms Meerlus and Kersfontein in the Paardeberg area near Wellingtonin 1998 on granite derived soils to investigate the effect of canopymanagement and fertiliser applications on berry K accumulation and winequality.Four fertiliser applications, three canopy treatments and a MgSO4 foliar spraywere studied. The three fertiliser treatments being: none (control), CaSO4,Ca(OH)2, and MgSO4 applications. The canopy treatments were: thin to twoshoots per bearer, tip, vertical shoot positioning (VSP) and the removal ofyellow leaves and lateral shoots (canopy 1), thin to three shoots per bearer,top after véraison and VSP (canopy 2) and VSP with top after véraison(canopy 3/control). Magnesium sulfate sprays were applied at véraison fortwo seasons (1999/00 and 2000/01).Seasonal effects produced the most significant differences in this experiment.Canopy treatments did not affect juice K concentration at harvest. Canopy 1and 2 produced significantly lower wine pH values at Kersfontein. Fertilisertreatments had no effect on juice K concentration nor did it affect winequality. Magnesium sulphate foliar sprays did not affect juice K concentration at harvest but significantly lowered juice and wine pH, improved wine colourdensity and total phenolic content.It appears for this experiment that soil K content before véraison, shootgrowth at and after véraison and water stress after véraison were the mainfactors determining juice K concentration at harvest.

[发布机构] Stellenbosch University