The prevailing wind direction and wind velocity are always considered when vineyards are established in a specific terroir.
Establishment is often forced towards geo-morphologically complex terroirs where climatic conditions are affected by aspect, slope and relief of the landscape. This further complicates decisions regarding the orientation of vineyard rows. According to the prevailing wind velocity and direction, the wind conditions between the rows and inside the canopies, as well as the air and canopy humidity, may be affected.
Vineyard and measurements
The effect of row orientation [North-South (NS); East-West (EW); North-East-South-West (NE-SW); North-West-South-East (NW-SE), each replicated five times on a flat site of approximately 3 ha] at fixed row (2.7 m) and vine (1.8 m) spacing, on climatic profiles of canopy and grapes of spur pruned (two buds) vertically trellised Shiraz/101-14 Mgt, was determined at the Robertson Experiment Farm of ARC Infruitec-Nietvoorbij in the Breede River Valley, a region that experiences semi-arid macroclimatic conditions. Due to low precipitation and inconsistent rain events in summer, vines were irrigated weekly at a volume of 14 mm during the high season period. A cover crop (rye) was sowed after harvest and killed before budding. Vines were uniformly managed and were only vertically shoot positioned and topped; both actions were performed on average three times per year. Meso- and microclimate profiles were continuously monitored during three consecutive seasons by means of sensors, and data logged. Meso-wind velocity (m/s) and -direction were recorded in the centre of the work row at a height of approximately 1.2 m and at a height of 1 m above the canopy/vineyard row. Micro relative humidity (%) was measured in the bunch zone.
PHOTO 1. Close-up view at treatment level of the experiment at Robertson Experiment Farm of ARC Infruitec-Nietvoorbij, Breede River Valley, Robertson, South Africa.
The temperature- and radiation macroclimate of the Breede River Valley was discussed in the companion article on the effect of row orientation on canopy light and temperature profiles. According to weather station data, the wind velocity is stronger during the active vegetative/flowering phase (November), whereas it decreased during the last month of the grape-ripening phase (March).
Wind velocity in differently orientated work rows decreased from October to March (Figure 1). The wind velocity patterns between the differently orientated rows were similar to that of the ambient prevailing wind, but the speed of the wind inside the vineyards was reduced to less than half of that of ambient. The incoming wind velocity was least affected by EW and NW-SE-orientated rows, whereas it was most reduced by the NS and NE-SW orientations. The NS orientation had the lowest diurnal values. Generally, it may be expected that terroir of the vineyard location and the vineyard per se would have a controlling effect on wind velocity prevailing in work rows. In this terroir, the wind increased in velocity in the inter-row spaces until late afternoon (18:00), whereafter it sharply decreased towards the night. Low wind velocity was maintained from after midnight until approximately sunrise. Wind velocity in NW-SE work rows seemed slightly higher during the afternoon, whereas that in EW-orientated rows seemed highest during the evening, followed by NW-SE, NE-SW and NS.
FIGURE 1. Meso hourly mean wind velocity in work rows of Shiraz/101-14 Mgt vineyard planted to four different row orientations at Robertson Experiment Farm of ARC Infruitec-Nietvoorbij.
Although it depends on air properties, a higher wind velocity would most likely have a faster cooling and drying effect on grapes. Along with a proper canopy microclimate, this may decrease the risk of diseases [such as Botrytis cinerea (grey rot) and Plasmopara viticola (downy mildew)], especially after intermittent summer rainfalls, and may favour the development of a better grape composition in hot and humid terroirs in particular. Consideration should, however, also be given to physical damage that may be caused by strong winds, especially during early growth phases, whereas inflorescence damage is a major concern regarding yields and sustainability. Furthermore, warm winds may lead to increased soil evaporation, a decrease in photosynthetic activity (closing of stomata), berry dehydration and the risk of weight loss (especially in the case of Shiraz). The implications may also not be favourable to quality grape composition. Row orientation choices (and canopy management) should therefore be carefully considered in such terroirs in order to obtain favourable compromises between vegetative growth, inflorescence development, berry development, grape exposure and impacting meso- and microclimatic factors affected by viticulture practices.
Prevailing wind direction measured on top and in work rows, showed a similar profile for the whole growth season (Figure 2). In the beginning of the season (October – November) wind maintained an S-SE direction during the night, changing progressively to S incoming towards early morning and then to SE incoming from mid-day onwards. After that, night-time winds shifted to SE, then to S during mid-morning to mid-day, whereafter it progressively reverted back to SE. These patterns of diurnal change stayed more or less the same for the different treatments throughout the season, but wind direction was clearly different for different row orientations. The patterns fit well with the occurrence of alternate valley and mountain breezes and materialises the effect of topography on the local air circulation. As canopies developed, impact of row orientation on wind flow between rows became clearer.
Diurnally, the main wind directions in NS-, NW-SE-, EW- and NE-SW-orientated work rows were S incoming; SE incoming changing to S incoming during late season; SE incoming; and E-SE incoming, respectively. Patterns may change in terroirs with different prevailing wind directions. The impact of row orientation on wind direction patterns together with wind velocity recordings between differently orientated rows are extremely important in decisions regarding vineyard establishment and expectations and interpretation of yields and berry mass, temperature, composition and health under different climatic conditions.
FIGURE 2. Meso hourly mean wind direction in work rows of Shiraz/101-14 Mgt vineyard planted to four different row orientations at Robertson Experiment Farm of ARC Infruitec-Nietvoorbij (trends are indicated on the figure in degree direction, whereas they are explained in the text by using the cardinal direction).
Despite higher wind velocity in work rows (Figure 1), canopy-interiors of EW-orientated rows tended to have higher relative humidity during morning periods (Figure 3). High humidity is commonly associated with high risk of P. viticola and B. cinerea development; wind velocity and low relative humidity have a greater effect than temperature on evaporative potential of ambient air and therefore control of pathogens. Too dense canopies are associated with high incidence and severity of grape rot and EW-orientated canopies in particular would therefore have to be managed judiciously in order not to compromise any other positive factors related to this row orientation. Even though VSP-vineyards are not common in table grape production and it may be argued that light microclimate profiles as shown in this study would not have similar impact on grape exposure in larger and more horizontal trellising systems used in table grape production, row orientation would be very important in steering wind velocity and direction in order to dry grapes after morning dew, to remove locked high humidity air that prevails after irrigation, and to feed the light-incoming/humidity existing windows; these are critical factors for table grape sanitary status and quality. To accomplish that, rows should therefore rather be orientated towards the incoming prevailing wind direction in such cases, especially when trellises are not high above the ground; this is plausible as table grapes are mainly produced in flat areas.
FIGURE 3. Micro hourly mean relative humidity of Shiraz/101-14 Mgt vineyard planted to four different row orientations at Robertson Experiment Farm of ARC Infruitec-Nietvoorbij.
- Judicious vineyard management during both pre- and post-véraison periods is required to minimise interference of biotic and abiotic factors with the contribution of row orientation in the control of vineyard wind and humidity profiles.
- Prevailing winds and humidity within selected terroirs would largely dictate profiles of these parameters within spaces.
- Results have global relevance in decisions regarding vineyard establishment and further management to reach product objectives in yield, grape sanitary status and quality.
Vineyard wind velocity and direction and canopy humidity profiles of differently orientated vertically trellised Shiraz grapevines (NS; EW; NE-SW; NW-SE rows) were investigated. Prevailing seasonal winds (switching between S and SE) and humidity within selected terroirs would largely dictate profiles. In this terroir, incoming wind velocity was least affected by EW and NW-SE rows and most reduced by NS and NE-SW orientations. The NS orientation had lowest diurnal values. Wind velocity in NW-SE work rows seemed slightly higher during the afternoon, whereas that in EW-orientated rows seemed highest during the evening, followed by NW-SE, NE-SW and NS. Judicious vineyard management is required to minimise interference of biotic and abiotic factors with row orientation impact and product objectives in yield, grape sanitary status and quality.
We would like to thank the Agricultural Research Council and South African wine industry (through Winetech) for funding. Our gratitude goes to personnel of the Viticulture Department (especially G.W. Fouché, A. Marais, C. Paulse and L. Adams) and farm personnel at Robertson Experiment Farm of ARC Infruitec-Nietvoorbij for their diligence and devotion. We would also like to extend our sincerest gratefulness to many international and local collaborators and specialists for their assistance and contributions in many ways. Special thanks also to M. Booyse of the Biometry Department of ARC. Details of this popular script can be found in the following scientific article (and the references therein):
Hunter, J.J., Volschenk, C.G. & Zorer, R., 2016. Vineyard row orientation of Vitis vinifera L. cv. Shiraz/101-14 Mgt: Climatic profiles and vine physiological status. Agricultural and Forest Meteorology 228, 104 – 119.
– For more information, contact Kobus Hunter at email@example.com.