Technical Yearbook 2023

A

B

Location of vineyard (red dot; A) on a convex hill where cold air drains away and uneven budding was observed, left; and location of a vineyard (green dot; B) in a concave valley landscape where there is significant cold accumulation and the vineyard budded well, right. The two GIS layers on the maps are the TPI and the flow accumulation model.

effect on cold-unit accumulation and could possibly be the cause of poor budding. Livestock like sheep tend to seek out these zones of higher nighttime temperatures to sleep in on cold winter nights. If planted in a concave cold-air drainage zone, a constant flow of cold air will move over the vineyard during the early winter morning hours. The bigger and higher the catchment area of the mountain, the more extensive and colder the “cooling effect” of the cold-air drainage will be. Just as the position of a dam is established to collect the maximum amount of water from the catchment area, so the best position for maximum cold-unit accumulation can be determined. This is exactly what was observed at the last Chardonnay discussion group: that the blocks located right next to dams usually bud well. The dam wall possibly pools up more than just water. The blocks that are planted outside of the cold air drainage zones on convex hills where cold-air accumulation cannot take place, were the blocks that struggled with uneven budding. The GIS models that correlated the strongest with the uneven budding, were terrain position index (TPI), terrain wetness index (TWI) and flow accumulation (FA). These maps can be compiled and form part of Vinpro’s terrain analysis product.

Conclusion The mere fact that correlations were found, does not mean that cold-air drainage or slope shape is the only reason for the budding pattern of the Chardonnay blocks investigated. The objective of the discussion was to think more holistically about cold units, taking into account the terrain position of a vineyard, and not looking blindly at weather station data in isolation. The recommendation is therefore to also consider the thermal belt when interpolating cold-unit cold-air drainage. This could possibly point out the risk of planting a cultivar like Chardonnay, which is more susceptible to poor or uneven budding, on a specific locality. 

Reference https://www.wineland.co.za/the-effect-of-mountainous-terrains-on-cold-unit-accumulation/

For more information, contact Heinrich Schloms, GIS specialist/soil scientist at heinrich@vinpro.co.za.

115

TECHNICAL YEARBOOK 2023