The sustainability of irrigation water sources for vineyards in the Barossa Valley, South Australia

Water availability, quality and security are major constraints on the long-term sustainable production of irrigated crops. The quality of native and imported water resources is declining in many regions which will potentially have severe adverse impact on irrigated agriculture including vineyards. We estimated water demand for irrigated vineyards in the Barossa (rainfall 440 mm) and Eden valleys (rainfall 599 mm) using the FAO-56 dual crop coefficient approach for six common soil types (sand over clay, shallow soil on rock, cracking clays, hard red brown, calcareous and gradational soil, and acid and shallow soil on rock) under the current (2000-2023) and future climate projections (2023-2051, RCP 4.5). A multi-component major ion chemistry model (UNSATCHEM) was used to investigate the long-term impact of various irrigation water sources (river, recycled, groundwater and their blends) on the four soil quality indicators (pH, EC, SAR and ESP) in different soils and the relative yield reduction in response to rootzone salinity. The model was equilibrated with the measured soil solution and exchange parameters for 72 years (1951-2023) to achieve a quasi-equilibrium state for each of the soil types. Management options such as leaching irrigation and gypsum use were also explored to mitigate the adverse impacts of the irrigation sources.

The modelled grapevine irrigation requirement varied with climate and soil types; and water demand increased significantly (10-45%) across the soil types under future climate projections. This drove an increase in regional water demand (28-32%) under future climate projections. A long-term risk assessment with the poorest quality water showed a grapevine yield reduction of 3-12 and 11-23%, with recycled and groundwater irrigation, respectively. These water sources increased the EC > 10dS/m, after 5-10 years of irrigation in the Barossa valley but maintained the soil salinity below the tolerance threshold for grapevines in the Eden valley, demonstrating the importance of higher rainfall for leaching salts.

Even irrigation with high quality river water can have the potential to increase exchangeable sodium percentage (ESP) above the threshold level (6%) for degradation of some soil types. Maximum levels of average rootzone SAR (6.5-18mmol/L^1/2) and ESP (14-52%) were observed under groundwater irrigation of cracking clay soils. The acid soil over rocks showed lower sodicity hazard than sand over clay, calcareous and gradational and hard red brown soils. Model simulations suggested that an annual leaching irrigation of 30mm in spring with good quality water and subsequent irrigaiton with recycled water (1.8dS/m) or groundwater (3.3dS/m) reduced the salinity below the grapevine tolerance level. However, leaching irrigation alone was not sufficient to ameliorate the irrigation induced high sodicity hazard. A soil ameliorant such as gypsum along with leaching irigation are needed to reduce the sodicity hazard.

Modelling predictions demonstrated that availability and quality of water resources has the potential to impact grapevine yield and soil quality indicators. Management options such as leaching irrigation and gypsum application are crucial for enhancing the long term sustainability of vineyards; but maintaining a secure source of good quality water is also important  to support the wine industry in the study region.