Water and salt balances in Padthaway wine region

Abstract

Sustainability of groundwater irrigation was the focus of this project conducted at Padthaway. Information which was generated will assist calculation of recharge rates and levels of groundwater salinity, thereby assisting future management decisions on a vineyard as well as regional scale.

Summary

Padthaway producers source irrigation water from a shallow local aquifer in which salinity has increased by about 75% in the last 25 years, prompting interest in quantifying evaporation plus salt and water fluxes below the irrigated root zone.

The space/time variations in canopy cover and spatial variability in soil type and depth required special techniques for quantifying the dynamics of water and salt balances. A micro-meteorological device using what is known as flux tower technology continuously logged data and over the three years of the project was moved to different blocks of vines to cover a range of grape varieties, vine architecture and soil types. This provided a clearer picture of vineyard evapotranspiration. In addition, drainage meters were used in two vineyards to provide point measurements of the volume of water draining below the root zone both under the vines and between rows. Salt accession into the groundwater was considered using a salt and water balance formula that considered salt concentrations of rainfall and irrigation water, volumes going into the ground and solutes in drainage water. Although it was found that drainage volumes were small compared with rainfall and irrigation or the amount of water used by the vines, it was considered a critical factor in terms of leached salts.

Outcomes have included means for calculating the effects of use of water from the aquifer and data which will complement a broader study of the region called the SA Department of Water, Land and Biodiversity Conservation Padthaway Salt Accession Project. There are also interesting illustrations for grape growers, including the tracking of the annual course of vineyard water use under the influence of climatic and phenological factors.