The impact of grazing by cattle on Vitis vinifera L. cv. Shiraz vegetative growth and metabolite profile

Abstract

Context and purpose of the study. Globally, vineyard cultivation uses conventional methods to manage pests, diseases and increase yield. This cultivation practice requires the use of synthetic agrochemicals and mechanisation which results in deterioration of the soil health, biodiversity and ecosystem functioning. Over the past decade there has been an increasing demand from the consumer to know more about the origin of the product. Therefore, the use of greener methods (organic, biodynamic and regenerative practices) became a topic of interest. Regenerative viticulture integrates livestock grazing, which is based on the principals of Allan Savory’s holistic management system, to enhance soil microbiology, carbon sequestration, and biodiversity. The purpose of this study was to study the effects of cattle grazing on grapevine vegetative growth, fruit quality and wine chemistry in Vitis vinifera L. cv Shiraz.

Materials and Methods. This study was conducted in the 2023-2024 growing season in a 1.13-hectare vineyard established in 1998. Shiraz clone (SH9C) grafted on 101-14 Mgt rootstock trained on a vertical shoot positioning (VSP) system vineyard with a drip system during critical phenological stages. A control – ungrazed vineyard rows and a treatment – grazed rows by Nguni and Dexter cattle breeds during August 2023. The grazing density for this vineyard was 64 cattle. Shoot lengths were determined at pea size (E-L 31), véraison (E-L 35), and ripeness (E-L 38). Individual berry weights and diameters were determined from 50 berries one week before harvest and at harvest. Bunch weights were recorded at harvest. The amino acids and tannin of the grape must and the final wine were determined.  Statistica 19.0.0 were used to analyse the data statically.

Results. A significant (p≤0.001) reduction in the shoot lengths and berry weights were observed in the grazed vineyard rows compared to the control. The phenological stage and sampling stage did not have an influence in the shoot lengths and berry weights. Arginine and Gamma-aminobutyric acid (GABA) concentrations were higher in the ungrazed vineyard rows. The Hydroxy-proline concentration in the final wine were higher in the grazed vineyard rows. Higher tannin concentration in the juice and the final wine were observed in the grazed vineyard rows. Overall, while grazing decreased yield likely due to an increased nitrogen content, it appears to enhance grape quality, particularly in amino acids and tannin concentration benefiting wine qualitative properties.