Winetech Technical Yearbook 2022

1. Altitude or mean height above sea level, affects the lapse rate (the rate at which temperature decreases with increasing height), the site’s wind exposure and the water pressure needed for irrigation. 2. Aspect or the direction which a slope faces, affects the amount and timing of solar irradiation received (eastern slopes get more sun in the morning, while western slopes get more sun in the afternoon), which significantly affects the daily temperature curve within the vineyard. South-facing slopes are colder than north-facing slopes in the Southern Hemisphere at the same altitude and nearby location. Aspects facing prevailing winds have a cooling effect, and aspects facing strong storm winds lie at risk of damage. 3. Slope steepness affects mechanical factors, such as tractor and harvest machine movement, need for terracing, subsoil drainage and erosion hazards. When the slope becomes too steep (> 11°), the construction of terraces must be considered since the use of tractors and other implements become too dangerous. The slope is vital in all aspects of farming. It will determine row direction for adequate drainage, mechanisation and labour intensity. Steep northerly slopes also receive more solar irradiation than flat ones. Although steeper slopes are more challenging to manage, these slopes are where some of the best wines in the world are grown. 4. Curvature is the form of the slope and it determines the surface drainage capability of that slope. Convex slopes redirect water and are well-drained, while concave slopes accumulate water and are usually wetter. Concave slopes also collect colluvium and organic matter from higher-lying areas. The soil on concave slopes tends to be deeper, more fertile and have a higher water holding capacity than soils on convex slopes. These sites are generally chosen for cultivars that ripen later, while early varieties prefer convex slopes. 5. Day length is the amount of time that direct sunlight exposure is received. It is measured in hours of sunlight for a specific day of the year. Sites with longer day lengths are usually on crests. Deep valley bottoms have the shortest day lengths created by the surrounding hills and mountains’ shadowing effect. The less the direct radiation duration is for

a site, the longer the cooling period will be during the night. Day length has an immediate effect on the crop’s available time for photosynthesis and night-time respiration. 6. Solar radiation is the number of photons that are emitted by the sun, and irradiation is the received amount that is measured on a specific surface. Altitude, latitude, slope orientation and angle of a particular surface (with respect to the sun) and atmospheric variables (thickness and permeability) all influence the amount of energy a site receives. This amount of received energy is measured in watt-hours/m 2 and is used by the leaves for photosynthesis. It is not directly correlated to ambient temperatures. Air molecules absorb this energy which leads to a rise in temperatures. Although higher altitudes receive more radiation, the less-dense air absorbs less energy, leading to lower temperatures at higher altitudes. 7. Surface hydrology is always essential on a farm and influences various farming activities such as drainage, erosion control, dam locality, etcetera. The water accumulation model shows the direction and accumulation of surface water according to the surface model. The darker blue lines will accumulate more water than the lighter blue lines. This model can help to identify erosion risk areas, install drainage and redirect water to dams. REFERENCES https://www.wineland.co.za/let-your-terroir-guide-your- farm-planning/

For more information, contact Heinrich Schloms at heinrich@vinpro.co.za.

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WINETECH TECHNICAL YEARBOOK 2022