Agriculture Reference
In-Depth Information
Although the duration and intensity of sunlight are not limiting in hotter
regions, such as in La Mancha, Spain, the Central Valley of California, and the
Murray-Darling region of Australia, excessive exposure of fruit to direct radiation
can cause sunburn and too rapid a rate of ripening. This problem can be managed
through row orientation and row spacing and by allowing more canopy shading.
Row orientation and tree belts are important for protection from wind damage in
some maritime areas (e.g., in many vineyard areas of New Zealand's North Island
and along the central and northern coast of California).
Slopes also induce cold air drainage, which helps to avoid damage to vines on
the slopes from low temperatures in winter and frost in spring. Most grape culti-
vars require at least 180 frost-free days, and frosts after bud burst can cause serious
crop losses. In undulating topography, cold air collects in valley bottoms, whereas
warm air rises. In mountain regions, such as central Virginia, the mid-slopes are
best for vines because cold air drainage makes the lower slopes and valley bottoms
frost-susceptible in spring. However, vines on the highest slopes are more likely to
suffer winter freeze damage (at temperatures of 2º-15ºC below zero), depending
on how well the vine tissue is acclimatized.
The movement of air of different temperatures (and hence density) can make
up a convection cell (figure 2.10). These cells also develop near large bodies of
water, such as lakes, large rivers, and estuaries. Because the specific heat capac-
ity of water is much greater than soil, a large water body is a greater heat sink
than nearby land, so that at night warmer air over the water rises, to be replaced
by cooler air draining from the land. The moderating effect of these convection
cells means that vineyards near large water bodies do not suffer the extremes of
temperature, either diurnal or seasonal, which occur in inland (continental) cli-
mates. Classic examples of this effect occur in the Médoc region, France, which
is bordered by the Gironde estuary to the east and the Bay of Biscay to the west,
theMargaretRiverregionofWesternAustralia,andtheMorningtonPeninsula
region, Victoria, Australia.
Cool air over the
land “drains” down
slope
Figure 2.10
Convection cells on a clear night for vineyards near a large
body of water
(White 2003).
