Agriculture Reference
In-Depth Information
sufficient to supply vine needs in midsummer (around veraison). Where overhead
sprinklers are used for frost avoidance in the vineyard, additional water may be
necessary.
Whether obtained from surface storage or underground, the water should be
analyzed for the following:
•pH
• Total salts (by
EC
) (section 7.2.2.1)
• Na, Cl, and B concentrations, for potential toxicities and effects on wine
quality (section 7.2.2.3)
• Ca, Mg, and carbonate concentrations for assessing water “hardness” and
for calculating the
SAR
of the water (section 7.2.3)
• Fe concentration, because precipitates of Fe(OH)
3
can block drippers and
even pipe lines (section 2.2.4.3)
General criteria for the salinity hazard of irrigation waters are given in section
7.2.2.1. Because irrigation water may be concentrated two- to threefold by evapo-
ration in the soil, water with
EC
1 dS/m (640 mg salts/L) should be avoided for
vines, except when salt-tolerant rootstocks are used. Drip irrigation permits the use
of water with higher
EC
values than water used in spray or flood/furrow irrigation.
Availability of Recycled Water.
Viticulture must compete for water with other
rural and industrial users. Increasingly, vignerons are seeking to use recycled wa-
ter, or wastewater from cities, especially for drip irrigation where there is no dan-
ger of the water contacting the fruit. For example, the McLaren Vale region of
South Australia has restricted use of groundwater, and irrigation with secondary-
treated sewage effluent is being introduced for up to 1500 ha of vineyards. The
effluent is relatively high in nutrients (approximately 20, 9, and 24 kg/ha of N,
P, and K for every 100 mm applied), so fertilizer inputs should be adjusted. Sim-
ilarly, Scotchman's Hill on the Bellarine Peninsula, Victoria, which has an annual
rainfall of approximately 500 mm, now uses “grey water” from a local sewage
works for drip irrigation, after water has been stored in holding lagoons for 18
months. The concentration of salts in such wastewater is relatively high (ca. 1400
mg/L), which can create problems after regular use in vineyards unless the soil is
leached during the winter to remove excess salts.
Slope, Aspect, and Presence of Water Bodies
Soil drainage is generally better on slopes than on flat lands and valley bottoms.
Slopes also provide
cold air drainage
, which helps to avoid excessively low tem-
peratures in winter and frost damage in spring. Vines require 200 frost-free days,
and frosts following bud burst can result in serious crop losses. Beginning in au-
tumn and throughout winter and spring, the sun's rays pass through a greater
thickness of the earth's atmosphere than in midsummer. This effect, which de-
creases the intensity of sunlight received by the soil and vegetation, is most marked
at the highest latitudes where vines are grown (45-50° N or S). At such latitudes,
steep slopes facing the equator also absorb more solar radiation than does flat land,
because the angle of incidence at the soil surface is closer to 90° (fig. 8.3).
Thus, depending on geology and topography, a predominantly southerly as-
pect in the Northern Hemisphere and a northerly aspect in the Southern Hemi-
sphere is important in cool climate regions, for example, Burgundy and Cham-
8.3.3
