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Hedgerow
Species
The
major
investment
in
alley
cropping
by
international
and
national
research
programs
is
largely
based
on
the
hypothesis
that
trees
improve
the
nutrient
status
of
soils
beneath
them.
In
alley
cropping,
hedgerow
woody
perennials
can
improve
soil
fertility
by
adding
nutrients
to
the
soil
and
reducing
nutrient
losses
from
the
system.
The
practice
of
periodic
lopping
of
the
hedgerows
and
addition
of
the
harvested
biomass
to
the
alleys
facilitates
the
transfer
of
nutrients
from
trees
to
crops
and
can
minimize
the
tree-crop
compettion
for
light,
water
and
nutrients.
It
is
important
to
note,
however,
that
most
farmers
place
higher
values
on
economic
and
social
factors
than
biophysical
factors
when
selecting
trees
for
their
crop
lands.
In
this
paper
we
focus
on
the
biophysical
issues
that
have
received
significant
attention
from
researchers
developing
the
concept
of
alley
cropping.
These
include:
nitrogen-fixing
and
fast-growing
species,
biomass
production,
litter
decomposition
and
nutrient
release,
Nitrogen-fixing
and
other
species
Commonly
used
hedgerow
species
in
the
humid
tropics
include
Cajanus
cajan,
Calliandra
calothyrsus,
Erythrina
spp.,
Flemingia
macrophylla,
Gliricidia
sepium,
Inga
edulis,
Leucaena
leucocephala,
and
Paraserianthes
(Albizia)
falcataria
and
Sesbania
sesban
(Fernandes
et
al.,
1993b).
Results
of
long-term
observations
carried
out
in
the
humid
and
subhumid
zones
of
southwestern
Nigeria
have
shown
that
at
low
altitude
on
high
base
status
soils
G.
sepium
and
L.
leucocephala
are
the
two
species
most
suitable
for
use
in
alley
cropping
because
they
can
be
established
easily
by
direct
seeding,
withstand
repeated
prunings,
produce
large
amounts
of
biomass
and
nutrients,
and
are
relatively
long-lived
(Kang
1993).
Flemingia
macrophylla
has
performed
well
in
the
humid
zone
on
acid
and
low
base
soils
(Kang
1993,
Evensen
1995).
| Nitrogen-fixing
and
other
species |
 |
 |
| Leucaena
leucocephala
-
cowpea |
Leucaena
leucocephala
-
corn |
| |
 |
| Inga
edulis
-
rice |
Using
nitrogen-fixing
leguminous
perennials
as
hedgerow
species
offers
the
potential
to
enhance
soil
nitrogen
status
via
biological
nitrogen
fixation
and
more
efficient
recycling
of
the
existing
soil
nitrogen
in
an
alley
cropping
system.
For
example,
reported
values
of
nitrogen
fixation
in
Leucaena
leucocephala
vary
from
20
to
200
kgN
ha-1
yr-1
(Peoples
and
Herridge,
1990).
Within
the
Leguminosae,
the
majority
of
the
trees
used
in
alley
cropping
are
nodulated
members
of
the
Pailionoideae
and
the
Mimosoideae,
forming
symbiotic
association
with
the
bacteria
Rhizobium
(Giller
and
Wilson
1991).
Selection
of
hedgerow
species
by
farmers,
however,
is
largely
based
on
criteria
other
than
the
amount
of
nitrogen
the
tree
can
fix,
e.g.,
biomass
yield,
root
distribution,
suitability
as
fodder
(leaf
chemical
composition),
and
potential
for
multiple
use.
Funded
by
a
grant
from
the
Cornell
Agroforestry
Working
Group
(CAWG)
and
the
Distance
Learning
Program
of
the
Cornell
International
Institute
for
Food,
Agriculture
and
Development
(CIIFAD).
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