Agriculture Reference
In-Depth Information
Figure 4.25
A white salt encrustation under a dripper line in a vineyard in Castilla
laMancharegion,Spain.
Saltaccumulationiscounteractedbycontrolledleachingtomaintainasalt
balance.Asdiscussedinbox4.11,thisinvolvescalculatingaleachingrequirement
(
LR
).he
LR
can be met through regular irrigation scheduling. However, with
wateringstrategiessuchasRDI,PRD,orSDI,deepdrainageduringtheirrigation
periodsisminimized.Leachingofaccumulatedsaltsthenneedstooccurduring
the period of winter dormancy, either through rainfall or a deliberate blanket irri-
gationwithgoodqualitywater.
It is important to distinguish between the
LR
andleachingfraction(
LF
),the
latterbeingtheactualfractionofappliedwaterthatpassesthroughtherootzone.
Ideally
LF
shouldequal
LR
, but because of variability in water application and
infiltration,
LF
is usually greater than
LR
, which means more water drains through
therootzoneinsomepartsofthevineyardthanisnecessaryforsalinitycontrol.
This occurs more commonly with flood and furrow irrigation because of poor con-
trolovertheamountsofwaterapplied(see“IrrigationMethods”inthischapter).
Overall Salinity Management
Good salinity management must consider not only a soil's salt balance but also the
offsite effects of salt. Unnecessary leaching of salts into drainage water creates salin-
ity problems for water users downstream. “Best-practice” irrigation must therefore
focusonthedualobjectiveofminimizingsalinereturnlowstostreamsandavoid-
ing salt buildup in the soil and in groundwater immediately below the soil.
