Agriculture Reference
In-Depth Information
Table 2.3
Common Expressions for the
EC
and Salt Concentration of Water
Expression
Units
Numerical equivalence
EC
value
deciSiemens (dS)/m
—
EC
value
milliSiemens (mS)/cm
Same as dS/m
EC
unit
microSiemens (μS)/cm
Multiply dS/m by 1000
Salt concentration
milligram (mg)/L
—
Partspermillion
microgram (μg)/mL
Same as mg/L
Note. EC
= electrical conductivity.
Because irrigation water is concentrated two- to threefold by evaporation
from the soil, water of
EC
more than 0.8 dS/m should be avoided for vines, except
where salt-tolerant rootstocks are used (see “Salt, Drought, and pH Tolerance,”
chapter 5). Less water is lost by evaporation with drip irrigation, so water of higher
EC
can be used than is acceptable for spray or flood/furrow irrigation. Subsurface
drip irrigation is even more conservative of water than surface drippers, and there-
fore water of higher
EC
is potentially suitable. However, salinity and sodicity may
build up in the irrigated soil under these conditions, as is discussed in “Leaching,
Salinity, and Sodicity Control,” chapter 4.
Other analyses recommended for irrigation water are
• pH
• Na,Cl,andboron(B)concentrations,forpotentialtoxicitiesandefects
on wine quality
• Ca,Mg,andcarbonateconcentrationsforassessingwater“hardness”
• Iron(Fe)concentration,becauseifgelatinousFeprecipitatesform,they
can block drippers and even pipelines
Knowing the concentration of Na, Ca, and Mg ions allows the irrigator to calcu-
late the sodium adsorption ratio (
SAR
) of the water, which is important for the
reasons outlined in box 2.4.
Reclaimed Water
Winegrowers may consider using reclaimed water when fresh water is in short sup-
ply. Reclaimed water is water from sewage works and processing industries that has
been treated to a standard appropriate for its intended use. This type of water is
being used successfully in wine regions that are reasonably close to a reliable source,
such as in McLaren Vale, South Australia. Because reclaimed water is relatively high
in nutrients (the water in McLaren Vale contains approximately 20, 9, and 24 kg/ha
ofnitrogen(N),phosphorus(P),andpotassium(K),respectively,foreveryML/ha
applied), fertilizer inputs to the vines should be reduced accordingly. However, the
