Response of Vitis vinifera L. cvs. Sauvignon blanc, Merlot and Shiraz to Deficit Drip-Irrigation Strategies in the Lower Olifants River Region of South Africa – Soil and Grapevine Responses

Response of Grapevines to Deficit Drip-Irrigation Strategies

Abstract

The annual rainfall in the Lower Olifants River region is only 140 mm. Water therefore is a scarce resource that needs to be used optimally, and grapevines require irrigation. To this end, the effect of drip irrigation strategies on the vegetative growth, yield and wine quality of different grape cultivars growing in this region were investigated in a field trial. Grapevines growing in a red, sandy soil were subjected to four different irrigation strategies. Control grapevines were irrigated at 30% readily available water (RAW) throughout the season (S1). A second irrigation strategy entailed irrigation at 30% RAW depletion before véraison, followed by 75% RAW depletion until harvest (S2). Grapevines were also irrigated at 75% depletion before véraison, followed by 30% RAW depletion until harvest (S3). The driest strategy was irrigated at 75% depletion throughout the season (S4). For all three cultivars, S4 reduced cane mass. Less irrigation before véraison tended to reduce Sauvignon blanc and Merlot yields. Irrigation at 75% RAW depletion during berry ripening reduced Shiraz berry mass substantially, which resulted in significant yield losses. Under the prevailing conditions, S4 produced the best sensorial Sauvignon blanc wine quality. Prominent fresh vegetative and subdued tropical fruit aromas contributed to better wine quality. Reduced irrigation during ripening improved the berry and spicy character of Merlot
and Shiraz wines, leading to better overall quality compared to
irrigation at 30% RAW depletion. If improved wine quality is the
primary consideration, drip-irrigated vineyards in the sandy soils of
the region should be irrigated at 75% RAW depletion.