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Leaf Wetting and Uptake of Fluid Foliar
P Fertilizers for Wheat
Courtney Peirce, Craig Priest, Evelina Facelli, Therese
McBeath, Victoria Fernández and Mike McLaughlin
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Tactical Foliar P Fertilization
Fertilizer P is a very high input cost and represents a
high financial risk to growers in regions with variable
seasonal rainfall
Tactical application as a “top-up” of P in good seasons
on marginally deficient soils
Higher efficiency of fertilizer P uptake through the
foliar route
Limit to the total amount of P that can be supplied
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Plant-related factors
• Leaf wettability
• Leaf surface morphology
Environmental factors
• Temperature
• Wind
• Relative humidity
Formulation factors
• Adjuvants
• pH of formulation
• Form of P
Major Factors Affecting Foliar Fertilizer Efficacy
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Plant-Related Factors
Morphology and foliar P uptake of:
Adaxial (upper) vs. abaxial (lower) leaf sides
Varying levels of P nutrition
Measured by:
Impressions of leaves using cyanoacrylate adhesive
Scanning Electron Microscopy of fresh and fixed leaves
Leaf wettability by static advancing and receding contact
angles
Tracer studies using 32P and 33P to give foliar-applied
fertilizers a unique fingerprint
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Foliar P Uptake Methods - Leaf Side
2 foliar application timings
ear emergence 39DAS and mid-anthesis 49DAS
3 32P and 33P labelled fertiliser rates (0.6, 1 and 2.6
kg P/ha)
33P applied to lower side
32P applied to upper side
Leaves not washed after treatment but
translocation reported as a % of foliar P recovered
in the plant
Plants harvested during maturity
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Wheat Leaf Scanning Electron Microscope Images -leaf side
Upper side Lower side
800x magnification: fresh leaves sampled at 44DAS
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Wheat Leaf Morphology – Leaf Side
LSD (P ≤0.05) side effect: stomata 2, trichomes 6
Upper leaf side
LI 700® (0.3% w v-1)
Contact Angle 113°
Lower leaf side
LI 700 ® (0.3% w v-1)
Contact Angle 80°
Upper
leaf side
Lower
leaf side
Stomata mm-2 51 ± 6 a 39 ± 4 b
Trichomes mm-2 45 ± 22 a 5 ± 4 b
Trichomes increase
surface roughness
and decrease leaf
wettability
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0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
adaxial abaxial
Tra
nsl
ocati
on
Untreated leaves
Stems
Heads
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
low mid high low high
Ear emergence Mid-anthesis
Tra
nsl
ocati
on
(% o
f fo
liar
P r
ecovere
d i
n p
lan
t)
Foliar P Translocation to Plant Parts – Leaf Side
a
b b
c c
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
adaxial abaxialT
ran
slo
cati
on
(% o
f fo
liar
P r
ecovere
d in
pla
nt)
a
b
P P P P P
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P
treatment
(kg P/ha)
Stomata
/mm2
Trichome
/mm2
Contact angle
of water(°)
Upper Lower Upper Lower Upper Lower
24 77c 59c 59c 7c 143.2b 117.7a
8 55b 39b 41b 3b 139.3ab 112.8a
0 36a 29ª 5ª 0a 123.2a 103.2a
Effect on P Nutrition on Leaf Surface Properties
Higher θ with upper leaf sides & higher trichome densities P deficiency decreases the leaf surface hydrophobicity
Fernández et al. (2014) “Effect of wheat phosphorus status on leaf surface properties and permeability to foliar-
applied phosphorus” Plant and Soil (in press)
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P
treatment
(kg P/ha)
Radioactivity recovered
Foliar P
Absorption (%)
Foliar P
translocated
from treated
leaf (%)
24 33ª 34ª
8 20b 35ª
0 0c 0b
24
8
0
Effect on P Nutrition on Foliar P Absorption
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Summary of Previous Experiments
Different surface morphology between leaf sides
Upper leaf side less wettable than lower leaf side
Higher foliar uptake from adaxial leaf side
Implication for crops with horizontal leaf orientation
P Nutrition affects morphology and wettability of leaves
Deficient leaves have less trichomes and stomata
Severely deficient leaves are unable to take up foliar-applied
P
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Plant x Formulation Mechanism
Foliar P in the form of orthophosphate
Charged anion but leaf surface hydrophobic
Phosphoric acid more penetrative than
ammonium phosphates
Use of adjuvants
Surfactants to increase retention on leaves
(spreading and lowering contact angles)
Humectants to keep nutrients in solution longer
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Experiment Protocol – Adjuvant Effect Contact angle measurements of water and fertilizers on
wheat leaves
GS early booting to early ear emergence
Concentrations ranging from 0.01 – 0.3 % w v-1
Adjuvants: Agral® (Active ingredient: 63% nonyl phenol ethylene oxide condensate)
LI 700 ® (Active ingredients: 35% w v-1 soyal phospholipids, 35% w v-1 propionic acid)
Genapol ® X-080 (Polyethylene glycol monoalkyl ether)
Short-term foliar uptake of phosphoric acid + adjuvant
1.85 % P w v-1 applied at mid-late booting
33P tracer added to fertilizers
Harvested 7 days after application
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Static Contact Angles – Adjuvant Effect
Genapol ® X-080 at 0.05 % w v-1
Water Contact
Angle (°)
Advancing 159 ± 6
Receding 149 ± 10
Wheat leaf surface is
superhydrophobic due to
high advancing contact angle
and small hysteresis
Advancing contact angle of water
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Adjuvant Effect on Leaf Wettability
0
30
60
90
120
150
180
0.00% 0.05% 0.10% 0.15% 0.20% 0.25% 0.30%
Ad
van
cin
g C
on
tact
An
gle
(°)
Adjuvant Concentration (% w v-1)
Water
LI700
Agral
Genapol
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94% of foliar applied P absorbed by the
leaves for all treatments 3% washed off the leaves
<3% not recovered
Plant separated into parts after washing
to measure translocation from treated area Treated leaf tip and base
Ear (from main stem)
The rest of the main stem
Tillers
Short-term Uptake of Foliar P -with Adjuvants
Leaf tip
Leaf base
Treated leaf
Tre
ated a
rea
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Short-term Translocation of Foliar P -with Adjuvants
0
10
20
30
40
50
60
70
80
Agral Genapol Li700
Tra
nsl
ocati
on
(%
of
spik
e in
pla
nt
parts
)
Tillers
Ear
Main Stem
Treated leaf base
Treated leaf tipab b a
c
b
a
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Summary– Effect of Adjuvant
Wheat leaves are superhydrophobic
Contact angle of fertilizers vary with different
adjuvants
Short-term uptake of P does not vary for adjuvants
with different contact angles
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Practical Implications
Without use of adjuvants, wheat leaves are very
difficult to wet resulting in loss of foliar fertilizer to
soil
The foliar uptake of P is high regardless of the
adjuvant used
The effect of time-to-drying vs. leaf coverage by
fertilizer should be further investigated
Possible trade-off helps explain the results from this study
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Any Questions?
Acknowledgements
Funding: Fluid Fertilizer Foundation, GRDC, CSIRO Flagship
Collaboration Fund
Adelaide Microscopy at North Terrace and Waite Campus
Technical assistance: Bogumila Tomczak, Colin Rivers, Pontus
Forsberg, Paula Guzman