Agriculture Reference
In-Depth Information
Flat
land
Oblique incidence
of sun's rays
Atmosphere
North
High angle of incidence
Steep
land
pole
of sun's rays
Conditions for winter
in the northern Hemisphere
South
pole
The influence of latitude and slope of land on received and absorbed solar radiation.
Figure 8.3
pagne in France and the Otago Valley in the South Island of New Zealand. Vine
rows in Burgundy usually run up and down the slope and are oriented east-west.
However, rows up and down the slope in clean-cultivated vineyards are suscepti-
ble to erosion (see fig. 7.14). But in the Rhinegau of Germany, another cool cli-
mate region, the preferred vineyard layout is for rows to run north-south on a
west-facing slope. In this region, morning fogs are common during the critical au-
tumn ripening period, but these usually clear by the afternoon, so a west- to south-
west-facing slope maximizes warming of the soil.
In hotter climates, such as southern Spain, the Central Valley of California,
and the inland irrigation areas of Australia, minimizing the exposure of fruit to
excessive direct radiation, which causes sunburn, is more important than maxi-
mizing soil warming. The positioning of rows may influence the susceptibility of
vines to fungal diseases in humid regions, because surface drying of foliage and
fruit is enhanced by wind turbulence when the rows are perpendicular to the pre-
vailing wind direction (Jackson 2000). Row orientation and the presence of tree
belts provide important protection from wind in maritime areas, for example, in
many of the viticultural areas of New Zealand and coastal regions of California.
In undulating topography, cold air drains from high points, down valley slopes
to valley bottoms, while warm air rises. In cool climates, this cold air drainage
makes vines on the lower slopes and valley bottoms susceptible to frost damage
at bud burst, and even at flowering. Similar “convection cells” are set up near sub-
stantial bodies of water, such as lakes, large rivers, and estuaries, as shown in fig-
ure 8.4. The water body is a greater heat sink than the nearby land, so warmer
air over the water rises, to be replaced by cooler air draining from the land. Due
