Foliar application of P. II. Yield responses of corn and soybeans sprayed with various condensed phosphates and P-N compounds in greenhouse and field experiments


Barel, D.; Black, C.A.

Agronomy Journal 71(1): 21-24

1979


Greenhouse and field experiments were conducted with corn (Zea mays L.) and soybeans (Glycine max L. Merr.) to evaluate the growth response of foliar sprays with several condensed phosphates and P-N compounds. The maximum concentration of P tolerated in solutions of tri- and tetrapolyphosphates applied as sprays in the greenhouse was 1.3% with corn and 1.1% with soybeans. The maximum concentration of P tolerated as orthophosphate was 0.5% with corn and 0.4% with soybeans. With soybeans, the yields of plants sprayed with various condensed P compounds significantly exceeded the yields of the unsprayed control, which would not be classed as P-deficient on the basis of the P content of the leaves. Spraying the plants, however, increased the P concentration in the leaves. Phosphoryl triamide produced the highest yields of above-ground dry matter of corn plants in an experiment in which several P-N compounds and condensed phosphates were brushed on the leaves. Several different condensed phosphates were sprayed on corn and soybeans in a field experiment on a fine loamy, mixed, mesic typic haplaquoll (Webster silt loam). An increase in yield of corn that was statistically significant at the 5% level was obtained from spraying. The yields with tri- and tetrapolyphosphate were, respectively, 760 and 754 kg/ha above the control yield of 10,234 kg/ha. With soybeans, the increase in yield due to treatment was significant at the 18% level, and the increase was equivalent to 256 kg/ha above the control yield of 3747 kg/ha.

Foliar
Application
of
P.
II.
Yield
Responses
of
Corn
and
Soybeans
Sprayed
with
Various
Condensed
Phosphates
and
P
-N
Compounds
in
Greenhouse
and
Field
Experiments'
D.
Barel
and
C.
A.
Black
2
ABSTRACT
Greenhouse
and
field
experiments
were
conducted
with
corn
(Zea
mays
L.)
and
soybeans
(Glycine
max
L.
Merr.)
to
evaluate
the
growth
response
of
foliar
sprays
with
several
condensed
phosphates
and
P
-N
compounds.
The
maximum
concentration
of
P
tolerated
in
solutions
of
tri-
and
tetrapolyphosphates
applied
as
sprays
in
the
greenhouse
was
1.3%
with
corn
and
1.1%
with
soybeans.
The
maximum
concentration
of
P
tolerated
as
orthophos-
phate
was
0.5%
with
corn
and
0.4%
with
soybeans.
With
soybeans,
the
yields
of
plants
sprayed
with
various
con-
densed
P
compounds
significantly
exceeded
the
yields
of
the
unsprayed
control,
which
would
not
be
classed
as
P
-deficient
on
the
basis
of
the
P
content
of
the
leaves.
Spraying
the
plants,
however,
increased
the
P
concen-
tration
in
the
leaves.
Phosphoryl
triamide
produced
the
highest
yields
of
above
-ground
dry
matter
of
corn
plants
in
an
experiment
in
which
several
P
-N
compounds
and
condensed
phosphates
were
brushed
on
the
leaves.
Several
different
condensed
phosphates
were
sprayed
on
corn
and
soybeans
in
a
field
experiment
on
a
fine
loamy,
mixed,
mesic
typic
haplaquoll
(Webster
silt
loam).
An
in-
crease
in
yield
of
corn
that
was
statistically
significant
at
the
5%
level
was
obtained
from
spraying.
The
yields
with
tri-
and
tetrapolyphosphate
were,
respectively,
760
and
754
kg/ha
above
the
control
yield
of
10,234
kg/ha.
With
soybeans,
the
increase
in
yield
due
to
treatment
was
significant
at
the
18%
level,
and
the
increase
was
equiva-
lent
to
256
kg/ha
above
the
control
yield
of
3747
kg/ha.
Additional
index
words:
Foliar
feeding,
and
nutrition,
P
absorption
and
translocation.
A
FTER
the
discovery
that
certain
condensed
phos-
phates
could
be
applied
foliarly
at
much
higher
concentrations
than
orthophosphate
to
corn
(Zea
mays
L.)
and
soybeans
(Glycine
max
L.
Merr.)
and
that
some
were
well
absorbed
and
translocated
(Barel
and
Black,
1978),
the
next
step
seemed
to
be
to
spray
whole
plants
to
determine
whether
this
type
of
P
nutrition
would
affect
plant
growth.
Because
only
limited
quan-
tities
of
the
most
promising
condensed
P
compounds
could
be
produced
readily
with
the
laboratory
-scale
equipment
available,
only
greenhouse
experiments
and
a
small
field
experiment
were
feasible.
Tukey
et
al.
(1956)
and
Wittwer
et
al.
(1956)
review-
ed
the
various
environmental
factors
that
affect
the
rate
of
absorption
and
translocation
of
nutrients
ap-
plied
to
the
foliage.
They
found
that
temperature,
air
humidity,
and
light
intensity
are
important.
These
con-
ditions
may
vary
widely
in
the
greenhouse
or
field.
Leaf
hairs
usually
have
thinner
cell
walls
or
less
1
Journal
Paper
No.
8954
of
the
Iowa
Agric.
and
Home
Eco-
nomics
Exp.
Stn.,
Ames,
Iowa.
Propect
No.
1868.
Contribution
from
the
Dep.
of
Agronomy.
Information
in
this
paper
was
presented
at
the
Annual
Meeting,
Soil
Science
Society
of
Amer-
ica,
Las
Vegas,
Nevada,
11-16
Nov.
1973.
Received
25
Oct.
1977.
2
Greenhouse
scientist,
Weyerhaeuser
Co.,
Western
Forestry
Research
Center,
Centralia,
Washington,
and
professor,
Dep.
of
Agronomy,
Iowa
State
Univ.,
respectively.
22
AGRONOMY
JOURNAL,
VOL.
71,
JANUARY
-FEBRUARY
1979
Table
1.
Approximate
maximum
concentrations
of
various
sources
of
P
tolerated
by
corn
and
soybeans
in
solutions
applied
to
the
foliage
by
spraying
with
damage
to
no
more
than
5%
of
the
leaf
area.
P
sourcet
Maximum
concentration
of
P
in
solution
for
indicated
plant
Corn
Soybeans
Orthophosphate
Pyrophosphate
Tripolyphosphate
Tetrapolyphosphate
Trimetaphosphate
Tetrametaphosphate
Polyphosphate
mixture
Na-Chars
9-18-9
0.5
0.8
1.3
1.3
1.3
1.4
0.9
0.6
0.4
0.7
1.0
1.2
1.2
1.3
0.7
OA
t
The
various
phosphates
were
added
in
the
ammonium
form
at
pH
7.
cuticle
near
their
bases
and
usually
are
relatively
ef-
fective
in
nutrient
uptake
(Linskens
et
al.,
1956).
Use
of
a
glass
rod
to
spread
the
solution
in
the
screening
experiment
might
have
caused
increased
damage
to
the
leaves
by
breaking
some
leaf
hairs
(Barel,
1975).
Accordingly,
an
experiment
to
determine
the
maxi-
mum
concentrations
of
certain
P
compounds
that
could
be
applied
to
plants
in
the
greenhouse
by
spray-
ing
was
conducted
before
the
experiments
were
done
in
which
the
growth
responses
were
measured.
The
quantities
of
the
P
-N
compounds
available
were
not
enough
to
do
a
complete
plant
-spraying
experi-
ment.
There
was
enough
material,
however,
to
treat
the
plants
by
brushing
on
the
solutions.
We
believed
that
some
evaluation
of
these
compounds
could
be
obtained
by
brushing
the
solutions
on
young
plants
and
then
measuring
growth
response
by
a
dry
-weight
determination.
The
objectives
of
the
work
reported
in
this
paper
were
1)
to
determine
at
what
concentration
the
P
compounds
that
proved
successful
in
the
screening
ex-
periments
(Barel
and
Black,
1977)
could
be
sprayed
on
corn
and
soybeans
and
2)
to
determine
whether
yield
responses
could
be
obtained
by
using
these
foliar
nutrient
P
sprays
in
greenhouse
and
field
experiments.
MATERIALS
AND
METHODS
Maximum
P
Spray
Concentrations
in
the
Greenhouse
Solutions
of
various
P
compounds
and
some
commercial
products
were
sprayed
at
different
concentrations
with
a
small
hand
-pump
sprayer
on
three
corn
and
three
soybean
plants
at
the
7
-leaf
stage
in
the
greenhouse.
All
solutions
were
at
pH
7
and
contained
0.1%
Tween
80.
The
applications
were
made
at
night,
and
the
plants
were
sprayed
so
that
both
sides
of
the
leaves
were
wet
and
dripping
nearly
occurred.
Estimates
of
damage
to
the
leaves
,on
the
basis
of
the
three
most
damaged
leaves,
were
made
10
days
after
application.
Response
of
Soybeans
to
Spraying
with
Various
Phosphates
in
the
Greenhouse
Soybeans
of
the
Hark
variety
were
planted
on
27
May
1972,
in
No.
10
cans
that
contained
3
kg
of
a
mixture
by
volume
of
2
parts
of
low
-P
soil
(the
Bray
P
i
test
was
10
kg/ha,
the
NI-1,0Ac
exchangeable
K
determined
on
undried
soil
was
86
kg/ha,
and
the
pH
was
6.5),
1
part
sand,
and
1
part
peat.
The
soil
was
thoroughly
mixed
with
200
ppm
of
N,
100
ppm
of
K,
and
20
ppm
of
P
as
NELNO.,
KNO
3
,
and
NI
-1
4
1-1
2
1
3
0
4
.
The
first
spray
was
applied
with
a
small
hand
-pump
sprayer
on
the
evening
of
28
June
at
85%
of
the
maximum
allowable
Table
2.
Yield
of
seed
per
plant,
seed
number,
weight
per
seed,
and
phosphorus
content
of
unsprayed
young
leaves
sampled
10
days
after
the
second
spraying
of
soybean
plants
with
vari-
ous
P
compounds
in
a
greenhouse
experiment.
Form
of
phosphatet
Pin
Yield
No.
of
Weight
unspray.xi
per
plant
seeds
per
seed
leaves
None
(0.1%
Tween
80)
Orthophosphate
Pyrophosphate
Tripolyphosphate
Tetrapolyphosphate
Trimetaphosphate
Tetrametaphosphate
Polyphosphate
mixture
g
mg
21.0
e*
170
e
124
ab
0.35
d
25.4
ab
201
abc
126
a
0.44
b
22.9
cd
193
cd
119
be
0.41
lx:
21.5
de
188d
114c
0.51a
26.1
a
206
ab
127
a
0.40
lx:
24.2
be
194
bcd
125
ab
0.44
b
25.0
be
199
abed
126
ab
0.44
b
26.3
a
205
abc
128
a
0.41
Ix:
Means
in
a
given
column
not
followed
by
one
or
more
common
letters
dif-
fer
significantly
at
the
5%
level
of
probability
by
the
DMR
test.
t
The
various
phosphates
were
added
in
the
ammonium
form
at
pH
7.
concentration
as
given
in
Table
1.
Leaves
were
sprayed
on
both
sides.
The
humidity
in
the
greenhouse
was
raised
close
to
saturation
by
closing
all
the
windows
and
running
the
water
sprinkler
system
under
the
greenhouse
benches
all
night.
The
experiment
was
arranged
as
a
factorial
design,
with
the
number
of
P
sprays
(either
two
or
three)
as
one
factor
and
the
various
P
sources
as
the
second
factor.
There
were
eight
replications.
The
experimental
unit
was
one
plant
in
one
pot.
The
second
spray
application
was
made
on
17
July
at
100%
of
the
maxim
um
allowable
concentration,
except
for
tripolyphosphate,
which
was
accidentally
applied
at
115%.
Leaf
samples
were
taken
from
the
unsprayed
youngest
mature
leaf
on
27
July
by
removing
three
leaf
discs
of
1.8
cm
2
with
a
cork
borer.
Total
P
analyses
were
made
as
described
previously
(Barel
and
Black,
1978).
Half
of
the
replicates
received
a
third
spray
application
on
31
July.
All
plants
received
nutrient
solutions
containing
50
ppm
N
and
25
ppm
K
on
the
basis
of
soil
weight
as
NH,NO.
and
KNO
3
on
20
July,
3
August,
14
August,
and
22
August.
Watering
was
stopped
on
5
September,
and
the
individual
plants
were
har-
vested
shortly
thereafter.
Leaf
-brushing
Experiment
with
P
-N
Compounds
Funk's
G-4444
corn
was
planted
on
29
March
in
a
low
P
-soil
mixture
in
No.
10
cans
in
the
greenhouse.
The
soil
was
fer-
tilized
with
200
ppm
N,
6
ppm
P,
and
100
ppm
K
applied
as
N1
-
1
4
N0
a
,
KNO
3
,
and
NFI
4
H
2
PO
4
.
A
completely
randomized
block
design
was
used
with
six
replications.
On
7
May,
the
plants
were
in
healthy,
but
slightly
P
-deficient,
state,
and
freshly
prepared
P
solutions
were
applied
to
both
sides
of
the
leaves
with
a
soft
brush.
The
total
amount
of
P
applied
per
replicate
of
one
corn
plant
was
estimated
at
S.
mg
(a
total
of
7
ml
of
a
solution
containing
0.74%
P
applied
to
six
plants).
All
solutions
contanied
0.1%
Tween
80.
About
two-thirds
of
the
solution
added
was
retained
by
the
leaves,
and
the
rest
dripped
off.
Thus,
the
amounts
of
P
re-
tained
on
the
plants
may
be
estimated
as
about
5.7
mg/corn
plant.
To
prevent
the
drops
of
solution
falling
from
the
leaves
from
reaching
the
soil,
the
pots
were
covered
with
paper
at
the
time
of
application.
The
P
compounds
applied
included
phos-
phoryl
triamide,
phosphonitrilic
hexaamide,
and
ammonium
trimetaphosphimate.
Neutral
solutions
of
the
ammonium
salts
of
orthophosphoric
acid
and
tripolyphosphoric
acid
were
included
among
the
treatments
to
make
possible
a
comparison
with
these
compounds
that
had
been
used
in
other
experiments.
The
P
treatments
were
repeated
on
19
May.
This
time,
the
corn
plants
received
13.6
mg
of
P/plant
(1
ml
of
solution
containing
0.74%
P/six
plants).
The
total
dry
plant
weight
was
deter-
mined
by
cutting
the
plants
at
ground
level
on
15
June
and
dry.
ing
them
at
65
C.
Field
-spraying
Experiment
The
experimental
site
was
on
the
Bruner
farm,
8
km
(5
mi)
west
of
Ames,
Iowa.
The
soil
was
a fine
loamy,
mixed,
mesic
ty-
pic
haplaquoll
(Webster).
Tests
of
samples
taken
in
mid
-April,
1972,
showed
a
pH
of
6.7,
22
pp2m
of
P
extractable
by
the
BAREL
&
BLACK:
FOLIAR
APPLICATION
OF
P.
II
Table
3.
Response
of
corn
to
phosphate
solutions
brushed
on
the
leaves
in
a
greenhouse
experiment.
Source
of
P
solution
brushed
on
the
leaves
Plant
Pin
leaf
Total
P
in
weight
samples
plants
mg
Control
13.83
c•
0.19
b
26.74
c
Ammonium
orthophosphate
20.48
ab
0.21
ab
43.65
ab
Ammonium
tripolyphosphate
19.82
ab
0.21
ab
41.51
abc
Phosphoryl
triamide
22.73
a
0.23
a
52.85
a
Phosphonitrilic
hexaamide
16.25
be
0.21
ab
34.02
be
Ammonium
trimetaphosphimate
20.47
ab
0.24
a
48.39
ab
Means
in
a
given
column
not
followed
by
one
or
more
common
letters
dif-
fer
significantly
at
the
5%
level
of
probability
by
the
DMR
test.
Bray
No.
1
method,
and
142
pp2m
of
exchangeable
K.
The
value
for
P
is
classed
as
low.
'Pioneer
3369A,'
a
long
-season
corn
with
high
yield
potential,
was
planted
on
10
May
1972,
in
75
-cm
rows.
'Wayne'
soybeans
were
planted
on
11
May
in
30
-cm
rows.
The
corn
received
225
kg
of
N/ha
before
plant-
ing,
and
the
soybeans
were
not
fertilized.
The
first
spray
treatment
was
made
with
a
hand
-pump
sprayer
on
20
June,
when
the
corn
was
about
60
cm
tall.
The
treat-
ments
were
control,
ortho-,
tripoly-,
tetrapoly-,
trimeta-,
and
tetrametaphosphate.
The
amount
of
P
applied
was
equivalent
to
8
kg
of
P/ha
in
a
volume
of
500
liters/ha.
All
solutions
contained
0.1%
Tween
80
and
were
neutralized
to
pH
7
with
ammonium
hydroxide
before
application.
All
the
condensed
P
sources
were
freshly
prepared
in
the
laboratory
according
to
procedures
given
by
Barel
(1975).
The
spraying
was
done
after
sunset
between
2000
and
1200
hours.
The
experiment
was
arranged
in
a
completely
randomized
block
design
with
six
blocks.
The
control
treatment
was
repli-
cated
twice
in
each
block.
The
corn
plots
were
single
rows
3
m
(10
ft)
long,
and
the
stand
was
thinned
to
14
plants/plot.
With
soybeans,
plots
2.13
m
(7
ft)
long
and
two
rows
wide
were
used.
All
individual
plots
were
surrounded
by
border
rows.
Leaf
samples
were
taken
from
the
unsprayed,
full-grown
young
leaves
on
20
July.
With
corn,
a
leaf
tip
30
cm
long
was
taken
from
each
plant
in
the
plot.
With
soybeans,
15
leaflets/plot
were
collected.
A
second
spray,
supplying
16
kg
of
P/ha,
was
applied
at
the
time
the
corn
was
tasseling.
To
ensure
that
the
corn
would
have
an
adequate
supply
of
N
and
K
with
the
wet
spring
and
summer
weather
of
1972,
the
corn
was
sidedressed
on
22
July
with
extra
N
and
K
in
amounts
equivalent
to
112
kg
of
each
element/ha
as
NH,NO
3
and
KNO
B
.
Soybeans
were
harvested
on
29
September,
and
the
corn
was
picked
on
30
September.
RESULTS
AND
DISCUSSION
Maximum
P
Spray
Concentration
in
the
Greenhouse
Table
1
gives
the
approximate
maximum
concen-
trations
of
various
sources
of
P
that
could
be
applied
by
spraying
the
solutions
on
the
foliage
of
corn
and
soybeans
in
the
greenhouse.
The
assumption
was
made
that
visual
damage
to
a
maximum
of
5%
of
the
leaf
area
was
acceptable.
The
5%
limit
is
quite
arbitrary
and
is
subject
to
experimental
verification.
The
con-
centration
of
tri-
and
tetrapolyphosphate
that
could
be
safely
applied
was
21/
2
to
3
times
greater
than
that
of
orthophosphate,
just
as
in
the
screening
experiments.
Soybeans
tolerated
only
two-thirds
to
three
-fourths
of
the
concentration
that
could
be
applied
to
corn.
Response
of
Soybeans
to
Spraying
with
Various
Phosphates
in
the
Greenhouse
The
yield,
seed
count,
and
seed
weight
might
have
been
affected
by
the
number
of
spray
treatments;
hence,
these
data
were
subjected
to
an
analysis
of
vari-
23
Table
4.
Phosphorus
percentages
in
young,
unsprayed
leaves
of
corn
and
soybeans,
and
yield
of
grain
with
foliar
applications
of
various
P
compounds
by
spraying
in
a
field
experiment.
P
formt
Corn
Soybeans
Grain
yield
Pin
leaves
Grain
yield
Pin
leaves
kg/ha
kg/ha
None
10,234
b•
0.32
3,749
0.37
b
Orthophosphate
10,686
ab
0.34
3,608
0.41
a
Tripolyphosphate
10,994
a
0.35
4,008
0.40
a
Tetrapolyphosphate
10,988
a
0.33
3,965
0.40
a
Trimetaphosphate
10,667
ab
0.34
3,682
0.41
b
Tetrametaphosphate
10,523
ab
0.33
3,931
0.41
a
Means
in
a
given
column
not
followed
by
one
or
more
common
letters
dif-
fer
significantly
at
the
5%
level
of
probability
by
the
DMR
test.
t
The
various
P
compounds
were
added
in
the
ammonium
form
at
pH
7.
ance.
There
was
no
significant
effect
of
the
number
of
spray
treatments,
however,
and
thus
it
was
not
necessary
to
consider
them
separately.
The
means
over
all
replications
are
given
in
Table
2.
With
all
P
sources
except
tripolyphosphate,
the
yield
per
plant
signifi-
cantly
exceeded
the
yield
of
the
unsprayed
control.
With
tripolyphosphate,
there
was
9%
leaf
damage
after
the
second
spray
treatment.
The
weight
per
seed
of
soybeans
(which
normally
is
little
affected
by
soil
fertility
treatments)
and
the
number
of
seeds
per
plant
were
significantly
lower
with
the
tripolyphos-
phate
spray
treatment
than
with
other
spray
treat-
ments,
confirming
the
damaging
effect
of
the
second
spray
on
the
yield.
The
P
was
absorbed
and
trans
-
located,
however,
as
indicated
by
the
high
P
percent-
age
in
the
young
leaves.
The
P
analysis
of
leaves
from
the
control
treatment
was
high
enough
to
suggest
that
P
was
not
a
major
limiting
factor.
deMooy
et
al.
(1973)
described
P
percentages
in
the
youngest
mature
leaf
from
0.16
to
0.25%
as
low
and
from
0.26
to
0.50%
as
sufficient.
Yield
Response
from
P
-N
Compounds
Table
3
gives
the
plant
weight,
the
P
content
of
young
unsprayed
leaves
11
days
after
the
first
applica-
tion,
and
the
total
amount
of
P
in
the
above
-ground
plant
tissue.
This
last
figure
was
calculated
on
the
assumption
that
the
P
percentage
in
all
the
above-
ground
plant
tissue
was
the
same
as
that
in
the
sam-
ples
of
the
youngest
mature
unsprayed
leaf.
Phosphoryl
triamide
gave
the
highest
yield
of
above-
ground
plant
material.
According
to
the
multiple
-
range
test,
the
yield
was
significantly
higher
than
those
obtained
with
the
control
and
phosphonitrilic
hexa-
amide
treatments,
but
it
did
not
differ
significantly
from
the
yields
obtained
with
ortho-
and
tripolyphos-
phate
and
ammonium
trimetaphosphimate.
Only
plants
treated
with
phosphoryl
triamide
or
trimetaphosphimate
had
a
significantly
higher
P
per-
centage
in
the
leaf
sample
than
did
the
control
plants
10
days
after
the
first
application.
Values
for
these
two
compounds,
however,
do
not
differ
significantly
from
the
corresponding
values
for
the
other
P
treat-
ments,
which
agrees
with
an
earlier
observation
that
the
translocation
of
various
P
compounds
was
relative-
ly
fast
and
equally
good.
In
this
experiment,
the
P
percentage
in
the
leaves
of
plants
with
all
treatments
24
AGRONOMY
JOURNAL,
VOL.
71.
JANUARY
-FEBRUARY
1979
was
in
the
deficiency
range,
an
observation
confirmed
by
the
visual
appearance
of
the
plants.
The
difference
between
the
calculated
total
amounts
of
P
in
the
above
-ground
parts
of
the
plants
on
the
control
and
phosphoryl
triamide
treatments
is
26.1
mg,
which
is
much
more
than
the
estimated
quantity
of
5.7
mg
of
P
applied
in
the
first
treatment.
Because
of
the
way
in
which
the
figures
were
obtained,
this
observation
may
signify
only
that,
in
this
experiment
with
young,
P
-deficient
plants,
there
was
a
decided
preferential
translocation
of
P
to
the
newly
develop-
ing
leaves.
Field
Experiment
with
Condensed
Phosphates
A
statistically
significant
increase
in
corn
yield
was
obtained
from
spraying
the
plants
with
condensed
phosphates
(see
Table
4).
The
yields
with
tripoly-
and
tetarpolyphosphate
were
762
kg/ha
above
the
control
yield.
There
were
no
significant
differences
in
the
P
percentages
in
the
leaves,
but
all
values
including
the
control
were
relatively
high.
Evidently,
there
was
lit-
tle
P
deficiency.
With
soybeans,
the
increase
in
yield
due
to
P
spray
treatments
was
significant
at
only
the
18%
level.
Orthophosphate
produced
the
lowest
yield,
even
lower
than
the
control,
which
may
be
a
consequence
of
about
10%
leaf
damage
after
the
first
spray.
Here,
the
P
percentages
were
increased
by
the
spray
treatments.
All
leaves
had
a
relatively
high
P
percentage,
which
in-
dicates
that
there
was
little
deficiency
of
P
in
the
plants.
LITERATURE
CITED
Barel,
D.
1975.
Foliar
application
of
phosphorus
compounds.
Ph.D.
Dissertation.
Iowa
State
Univ.
Univ.
Microfilms.
Ann
Arbor,
Mich.
(Diss.
Abstr.
36B:3153).
----,
and
C.
A.
Black.
1978.
Foliar
application
of
phos-
phorus:
I.
Screening
of
various
inorganic
and
organic
phos-
phorus
compounds.
Agron.
J.
71:15-21.
deMooy,
C.
J.,
J.
Pesek,
and
E.
Spaldon.
1973.
Mineral
nutri-
tion.
In
Soybeans:
Improvement,
production,
and
uses.
Am.
Soc.
of
Agron.,
Madison,
Wis.
Linskens,
H.
F.,
W.
Heinen,
and
A.
L.
Stoffers.
1965.
Cuticula
of
leaves
and
the
residue
problem.
Residue
Rev.
8:136-178.
Tukey,
H.
B.,
S.
H.
Wittwer,
F.
G.
Teubner,
and
W.
G.
Long.
1956.
Utilization
of
radioactive
isotopes
in
resolving
the
ef-
fectiveness
of
foliar
absorption
of
plant
nutrients.
Proc.
Int.
Conf.
Peaceful
Uses
Atomic
Energy
12:138-143.
United
Na-
tions,
New
York.
Wittwer,
S.
H.,
H.
B.
Tukey,
and
F.
G.
Teubner.
1956.
Current
status
of
nutritional
spraying
as
revealed
by
radioactive
iso-
topes.
J.
Calif.
Horde.
Soc.
17:50-57.