Agricultural
Water
Management
110 (2012) 84–
93
Contents
lists
available
at
SciVerse
ScienceDirect
Agricultural
Water
Management
jo
u
r
n
al
hom
ep
age:
www.elsevier.com/locate/agwat
Replicated
lysimeter
measurements
of
tracer
transport
in
clayey
soils:
Effects
of
irrigation
water
salinity
T.H.
Skaggs
∗
,
D.L.
Suarez,
S.
Goldberg,
P.J.
Shouse
1
U.S.
Salinity
Laboratory,
USDA-ARS,
Riverside,
CA,
United
States
a
r
t
i
c
l
e
i
n
f
o
Article
history:
Received
30
September
2011
Accepted
2
April
2012
Available online 26 April 2012
Keywords:
Solute
transport
Salinity
Leaching
requirement
Lysimeter
a
b
s
t
r
a
c
t
Recent
studies
suggest
that
standard
guidelines
for
managing
salinity
in
irrigated
agriculture
overesti-
mate
the
leaching
requirement.
Transient-state,
process-based
model
analyses
offer
the
possibility
of
more
efficient
water
and
salinity
management,
but
data
are
needed
to
evaluate
the
accuracy
of
vari-
ous
subcomponents
of
the
models.
In
this
study,
tracer
(Br)
transport
in
twelve
lysimeters
identically
packed
with
clayey
soil
materials
was
monitored
at
eight
soil
depths
and
in
drainage
waters.
In
the
first
phase
of
the
experiment
(the
salinization
phase),
six
of
the
lysimeters
were
irrigated
with
high
EC
waters
(8.1
dS
m
−1
)
and
six
with
low
EC
waters
(0.4
dS
m
−1
).
In
the
second
phase,
all
lysimeters
were
leached
with
low
EC
waters
(0.4
dS
m
−1
).
Tracer
transport
was
very
different
in
the
high
and
low
EC
irrigation
treat-
ments,
with
the
high
EC
treatment
exhibiting
significant
tailing
in
the
breakthrough
curves.
Due
to
the
replicated
experimental
design,
it
was
possible
to
confirm
that
the
differences
between
the
experimental
treatments
were
significant
and
not
due
to
random
deviation.
Future
research
aimed
at
placing
realistic
confidence
levels
on
model
predictions
will
allow
transient-state
models
to
reach
their
full
potential
as
water
and
salinity
management
tools.
Published by Elsevier B.V.
1.
Introduction
For
many
decades,
guidelines
for
managing
salinity
in
irrigated
agriculture
have
emphasized
the
leaching
fraction
(LF)
and
leach-
ing
requirement
(LR)
concepts,
where
LF
is
the
fraction
of
irrigation
water
that
percolates
below
the
root
zone
during
a
growing
season
and
LR
is
the
minimum
LF
that
is
required
to
maintain
the
root
zone
salinity
at
a
level
that
does
not
reduce
yields
(U.S.
Salinity
Laboratory
Staff,
1954;
Rhoades,
1974;
Ayers
and
Westcot,
1985).
Several
recent
articles
(e.g.,
Letey
and
Feng,
2007;
Corwin
et
al.,
2007;
Dudley
et
al.,
2008;
Ben-Gal
et
al.,
2008;
Letey
et
al.,
2011;
Suarez,
2012)
have
noted
various
shortcomings
associated
with
the
LR
approach
to
salinity
and
water
management,
many
of
which
stem
from
the
fact
that
the
LR
approach
is
based
on
a
steady-
state
analysis
of
irrigation,
drainage,
crop
salt
tolerance,
and
root
water
uptake.
Recently,
a
University
of
California
Center
for
Water
Resources
workgroup
concluded
that
steady-state
analyses
over-
estimate
both
leaching
requirements
and
the
negative
impacts
of
irrigating
with
saline
waters
(Letey
et
al.,
2011).
Thus
the
guidelines
∗
Corresponding
author
at:
U.S.
Salinity
Laboratory,
450
W.
Big
Springs
Rd.,
River-
side,
CA
92507,
United
States.
Tel.:
+1
951
369
4853;
fax:
+1
951
342
4964.
E-mail
address:
todd.skaggs@ars.usda.gov
(T.H.
Skaggs).
1
Retired.
encourage
overirrigation,
which
wastes
water
and
increases
con-
taminant
transport
to
groundwater.
The
workgroup
recommended
that
transient-state
analyses
be
developed
to
promote
more
effec-
tive
water
and
salinity
management
(Letey
et
al.,
2011).
Transient-state
analyses
of
leaching
requirements
can
be
gen-
erated
using
computer
simulation
models
such
as
UNSATCHEM
(Suarez
and
Simunek,
1997),
HYDRUS
(
ˇ
Sim
˚
unek
et
al.,
2005),
ENVIRO-GRO
(Pang
and
Letey,
1998),
SWAP
(van
Dam
et
al.,
2008),
and
MACRO
(Jarvis,
1994).
These
mathematical
models
simulate
water
flow
and
chemical
transport
processes
in
irrigated
soils,
and
can
account
for
dynamic
factors
such
as
irrigation
scheduling
and
seasonally
variable
irrigation
water
quality
and
crop
salt
tolerance
(Oster
et
al.,
2012).
From
a
macro-perspective,
reducing
leaching
fractions
and
making
greater
use
of
marginal
quality
waters
should
lead
to
water
savings
and
reduced
groundwater
pollution.
From
a
micro-
perspective,
water
(and
cost)
savings
should
also
result,
but
it
will
involve
operating
farms
at
salinity
levels
that
are
closer
to
the
mar-
gin
where
yields
(and
revenues)
are
expected
to
diminish.
In
this
context,
it
is
reasonable
to
consider
the
accuracy
of
transient-state
model
predictions
and
the
precision
with
which
the
outcomes
of
different
management
scenarios
can
be
predicted.
If
a
transient
model
predicts
growth
conditions
that
will
just
allow
for
maximum
or
acceptably
high
yields,
how
much
confidence
should
be
placed
in
that
prediction?
0378-3774/$
–
see
front
matter.
Published by Elsevier B.V.
http://dx.doi.org/10.1016/j.agwat.2012.04.003