Agriculture Reference
In-Depth Information
Slope, Aspect, Nearness to Water, and Heat Input
Slope combined with aspect is important for maximizing the amount of solar
radiation received by vineyards at higher latitudes (between 40
o
and 50
o
N or S).
As shown in figure 4.16, chapter 4, part of the radiation absorbed at the land sur-
face warms the soil. The sun's rays pass through a greater thickness of the earth's
atmosphere at high latitudes than at the equator, which means the intensity of
sunlight received by soil and vegetation is less at these latitudes. The decrease in
sunlight intensity is greater during autumn through winter into spring. However,
because steep slopes that face toward the equator receive sunlight at a larger angle
of incidence than flat land, their potential for absorbing radiant energy and soil
warming is greater. Figure 2.9 illustrates these effects.
For these reasons, the most favored sites in cool-climate regions are pre-
dominantly south-facing slopes in the northern hemisphere and north-facing
slopes in the southern hemisphere. However, this generalization needs to be
modified for particular regions, such as in the Côte d'Or in Burgundy, where,
because of the local topography, many of the slopes are east-facing. Unusually,
in the cool Rhinegau region of Germany, west-facing slopes are preferred
because during the critical autumn ripening period, morning fogs are com-
mon, which usually clear by afternoon to the benefit of vines on west and
southwestern slopes.
Flat
land
Oblique incidence
of sun's rays
Atmosphere
North
pole
High angle of incidence
of sun's rays
Steep
land
Conditions for winter
in the northern Hemisphere
South
pole
Figure 2.9
The influence of latitude and land slope on the amount of
solar radiation received and absorbed at earth's surface (White 2003).
