Relationships between vineyard soil physiochemical properties and under-vine soil cover as potential drivers of terroir in the Barossa

Aims: Soils are an intrinsic feature of the landscape and have influenced culturally and economically important terroir delineation in many wine-producing regions of the world. Soil physiochemical properties govern a wide array of ecosystem services, and can therefore affect grapevine health and fruit development. These physiochemical properties can reflect a combination of factors, including geology and environmental conditions, as well as soil management. In order to evaluate to what extent each of these factors contribute to the soil-driven aspect of terroir, this study examines soil properties and under-vine soil cover of twenty-four vineyard sites located in six sub-regions within the Barossa Geographical Indication (GI) Zone in South Australia. The aims of this study are to investigate relationships between soil properties and soil management as potential features that shape sub-regional variation in terroir characteristics that may eventuate in the development of smaller, distinctive sub-regional GI’s within the Barossa GI Zone.

Methods and Results: Soil samples were collected from the under-vine rows of twenty-four vineyard sites, with four sites located in each of the six Barossa sub-regions of Central Grounds, Southern Grounds, Northern Grounds, Western Ridge, Eastern Ridge and Eden Valley. Soil physiochemical properties such as texture (% sand, % silt, and % clay), total carbon (TC), total nitrogen (TN), plant-available (Colwell) phosphorus (P), pH, electrical conductivity (EC), and gravimetric water content (GWC) were measured at each site. Under-vine soil cover at each vineyard site was then assessed by using 1m² quadrat surveys to categorise the under-vine zone based on the dominant plant species (perennial grasses or broadleaf weeds) or soil cover (bare soil or mulch). Results indicated that the Eden Valley had lower P than the Eastern Ridge and lower % clay than the Eastern Ridge and Central Grounds. The other measured soil properties were not different between the sub-regions. Under-vine floor cover did not play a significant role in shaping the measured soil properties in this study, instead it appears that soil texture was the main driver that explains these relationships. 

Conclusions:

Sub-regional variation in soil properties in the Barossa GI Zone was most strongly influenced by soil texture, which was variable at the sub-regional level in most of the sub-regions, however differences were found between the Eden Valley, Central Grounds and Eastern Ridge with the latter two sub-regions being characterised by soils with higher clay contents. Plant-available P was lowest in the Eden Valley, which could be explained by the higher sand content and therefore higher P leachability of soils in this sub-region. Under-vine soil cover did not have any effects on soil physiochemical properties between the vineyard sites, also likely because of the variability of soil texture between sites. The next steps in this study are to characterise the structure of soil microbial communities (i.e. microbiomes) in these six sub-regions to gain insight on how soil biogeography changes over an Australian wine-producing landscape. 

Significance and Impact of the Study: This study provides insights as to the main drivers of soil sub-regional variation in the Barossa GI Zone and indicates that soils are highly variable even at the sub-regional level.