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Improving Micronutrient Fluid Fertilizers using Novel Chelating Agents
Mik M L hli 1 2 d S l St 1Mike McLaughlin1,2 and Samuel Stacey1
1Earth and Environmental Sciences, The University of Adelaide, AUSTRALIA 2CSIRO L d d W t U b AUSTRALIA2CSIRO Land and Water, Urrbrae, AUSTRALIA
Areas of the world prone to micronutrient deficiency
Stubble where no zinc was applied has a dirty, grey appearance, compared with the stubbles to which zinc was addedadded
Zinc deficient crops later in ripening.Zinc deficient crops later in ripening.
Reactions of micronutrients in soils
PbpK18 0
Soils are predominantly negatively chargedbe
d
PbCu
Zn
8.08.0
9.0 negatively charged, and sorb trace elements very t l i llt s
orb
Co
Ni
9.5
9 6 strongly, especially in alkaline soils
Am
oun Ni
Mn9.6
10.6
M2+ + H2O
= MOH+ + H+
A
pH6 7 8
Reactions of micronutrients in soils
Trace elements also form very insoluble precipitates in soils, especially with phosphate, carbonate and hydroxide ions. This is a
ti l bl i h h ti f tili f l ti i lk liparticular problem in phosphatic fertiliser formulations in alkaline soils, where P concentrations in the fertilised band are high.
Compound pKsp
CaCO3 1.0 X 10-8.3
Cu(OH)2 1.6 X 10-19
CuCO 1 4 X 10-10CuCO3 1.4 X 10 10
Cu3(PO4)2 1.4 X 10-37
Mn(OH)2 2.0 X 10-13
MnCO3 2.2 X 10-11
ZnCO3 1.5 X 10-10
Zn(OH)2 1.2 X 10-17( )2
Zn3(PO4)2 9.0 X 10-23
Compatibility issues
Solubility of ZnO in polyphosphate solutions (from Mortvedt, 1991).
Polyphosphate contentFertiliser Solution pH5.0 6.0 7.0Polyphosphate content
(% of total P) ------------------ % Zn ------------------40 0.6 1.3 1.650 0.7 1.6 1.960 0.7 1.7 2.070 0.7 1.7 1.680 0.7 1.4 2.6
Chelates used to complex micronutrient ions
Organic molecules that complex micronutrient (metal) cations
Alters the charge of the fertiliser ion, which changes its fate in soil and affects absorption by plantsp y p
-
Zn2+ + EDTA4- ZnEDTA2-
soilsoil22
ZnEDTAZnEDTA22-- Electrostatic repulsion-
--
-ZnZn2+2+
Adsorption & fixation-
Problems with anionic chelates
ZnEDTAZ 2+
Charge reversal allows the cation to be mobile in the soil environment
Zn2+
the soil environment (subject to wash off/leaching)
Zn = 50nM
In nutrient solution
Plants do not absorb–vely charged metal-chelate complexes c
upta
ke
ZnT = 50nM
chelate complexes readily due to negative membrane potentials
Zinc
EDTA added to solution
Current Trace Element Fertilizers
Limitations to their effectiveness:Current trace element fertilizers are relatively ineffective on yalkaline and calcareous soils, where micronutrient deficiencies are most severe;
Synthetic chelates (e.g. EDTA) are not readily absorbed by roots due to membrane exclusion;
Negatively charged complexes may be electrostatically repelled from plant roots;
Product cost has mainly limited their use to high-value crops.
Environmental Pollution:EDTA is a persistent substance, has been found ubiquitously in the environment and has caused environmental degradation;
NTA is carcinogenic and has been banned in the USA.
Requirements for effective micronutrient fertilizers
Reduce trace micronutrient adsorption or precipitation.
Increase solution metal concentration (to aid mass flow and diffusion))
Increase labile pool of metal in soil
Membrane permeable or actively transported by root uptake mechanisms (minimises –ve charge on metal complex)
Environmentally friendlyEnvironmentally friendly
Inexpensive
Rhamnolipid: a ‘lipophilic’ chelate
Rhamnolipid is a biological chelating agent produced by bacteria;
Non-toxic, biodegradable, can be synthesised or purchased;
Product complexes trace elements (Zn, Cu, Mn etc) into a ‘lipophilic’ state;
The chelate can be readily absorbed by plant roots;
Less prone to leaching or surface runoff than EDTA and DTPALess prone to leaching or surface runoff than EDTA and DTPA.
Micelle + Trace ElementsRhamnolipid Monomer Elements
Hydrophilic HydrophobicHydrophilic HydrophobicHead tail
R1 Rhamnolipid biosurfactant
Metal complexing
Hydrophobic
complexing group
OH Hydrophobic groups
OH
R2 Rhamnolipid – second rhamnose sugar
Polyethyleneimine - PEI: a plant-available polymer?
Chelating polymer with an extremely high complexing capacity for trace elements (chelate rates could be reduced by 75%);
Used for transmembrane delivery of DNA and other pharmaceuticals
Less prone to leaching or surface runoff than EDTA;
Ethyleneamine Polyethyleneamine
Cu2+ complexing capacity of EDTA and PEIChelate
(g Cu2+/g chelate)Max. Complexing Capacity
PEIEDTA
1.490.37
Measuring lipophilicity of rhamnolipid
hydrophobic phase
Normally used to measure biomagnification potential of pesticides and other organic chemicals
[Fert] octanol
phasechemicals
Ko/w = [Fert] octanol[Fert] water
Water phase
CuSO4 CuSO4 +rhamnolipid
Lipophilic complexes with rhamnolipid
25Zn
20
ZnCuMn
15
Ko/
w
Mn
5
10K
0
5
Rhamnolipid EDTA PEI SO42-
Response of Zn deficient to rhamnolipid: Glasshouse trial on calcareous soil in Turkey (Ismail Cakmak)
Response of Zn deficient soil to PEI: Glasshouse trial in Turkey (Ismail Cakmak)
Response of Zn deficient soil to PEI: Glasshouse trial in Turkey (Ismail Cakmak)
Wheat dry matter response to rhamnolipid.Bars denote L.S.D. (p ≤ 0.05)
0.85 Durum wheat
(g/p
lant
)
0.75
0.80Bread wheat
rodu
ctio
n (
0 65
0.70
y M
atte
r pr
0.60
0.65
Dry
0.50
0.55
Rhamnolipid concentration (mg/kg)
0 2 4 6
Effect of rhamnolipid application on Zn uptake by bread wheat. Bars denote LSD (P ≤ 0.05)
/kg) 35 0.18Shoot Zn concentration
atio
n (m
g
25
30
(mg/
pot)
0.14
0.16Total Zn in shoots
conc
entra
15
20
sho
ots
(
0.10
0.12
hoot
Zn
c
5
10
15
otal
Zn
in
0 06
0.08
0.10
0 2 4 6
Dry
Sh
0
5 To
0.04
0.06
Rhamnolipid rate (mg/kg soil)Rhamnolipid concentration (mg/kg soil)
Glasshouse trial on Zn uptake by canola
The new products are more effective trace element fertilizers than EDTA on alkaline and calcareous soils.
Alkaline sodosol
Highly calcareous (39% CO )10
12
s)
Birchip soilHighly calcareous (39% CO3)
8
10
Zn/g
sho
ots Streaky Bay soil
4
6
upta
ke (µ
g
0
2Zn u
OZnSO4 EDTA Rhamnolipid PEI4
Absorption of Zn complexes by canola roots
EDTA, rhamnolipid and PEI compared as Zn chelantscompared as Zn chelants
Canola plants, kinetic uptake of chelated fertilizers Zinc speciation determined by
Anodic Stripping Voltammetry
New chelates are readily absorbed by plant roots
Both new products were readily taken up by canola roots.
Zn EDTA was excluded at the root membrane surface and not readilyZn EDTA was excluded at the root membrane surface and not readily absorbed by canola.
Uptake of Zn by canola roots in solution culture
2
2.5
/g ro
ot)
1
1.5
c Zn
( µg
Zn/
0
0.5
Sym
plas
ti
0ZnCl2 EDTA PEI Rhamno
New chelates are readily absorbed by plants
Zn PEI was readily absorbed and translocated to canola shoots.
Zn EDTA was not taken up by the plants.
0.8t)ot)
Zn EDTA was not taken up by the plants.
PEI (R2 = 0.51)
0.6
µg Z
n/g
shoo
tg
Zn/g
sho
o
EDTA (R2 = 0.77)0.2
0.4
Zn in
sho
ot ( µ
n sh
oot (
µg
00 20 40 60
ASV labile Zn (µg/L)
Z
ASV Labile Zn (µg Zn/L)
Zn i
(µg )
Chelated Zn Free Zn
Zinc distribution and speciation in canola roots
13-BM at the Advanced Photon Source, Argonne National Laboratory.
Zn mapped in root cross-sections using X-ray Microprobe fluorescence;
Zn speciated using X-ray Absorption Fine Structure Spectroscopy.
Synchrotron Zn X-ray fluorescence maps
ZnSO4 Zn signal (counts/s)
75 225 375 500 625 750
Z Rh li idZn-Rhamnolipid
Zn-EDTA
Zinc distribution and speciation in roots from different fertilizer sources
Zn signal (counts/s)
75 225 375 500 625 750Zn-PEI
65.6% Zn-phytate25.8% Zn-lysine
95 2% Zn phytate95.2% Zn-phytate3.1% Zn-glutamate
XAS speciation of Zn in ZnSO4 treated root sections
ZnSO4ZnSO4
77% Zn-phytate77% Zn phytate23% Zn-proline
Zn was predominantly stored in the root as Zn-phytate
XAS speciation of Zn in Zn-EDTA treated root sections
81.2% Zn-phytateZn-EDTA enhanced image18.8% Zn-glutamate
Zn EDTA was not detected inside the
Zn was predominantly stored in the root
Zn-EDTA was not detected inside the root symplast;
p yas Zn-phytate, even at low (environmentally relevant) Zn levels.
XAS Zn speciation in controls (no Zn)
84.4% Zn-phytate 15 6% Zn glutamate15.6% Zn-glutamate
XAS speciation of Zn in Zn-rhamnolipid treated root sections
Zn-Rhamnolipid61.3% Zn-rhamnolipidp24.4% Zn-proline14.3% Zn-phytate
80.0% Zn-rhamnolipid16.1% Zn-phytate3.9% ZnSO4 (or Zn2+)
Zn was predominantly found in the root as Zn-rhamnolipid, rather than Zn-phytate;
Intact Zn-rhamnolipid may have been absorbed by roots.
Canola field response to PEI in Southern Australia
+ PEI - PEI
Conclusions
Rhamnolipid formed lipophilic complexes with micronutrients and PEI has a high metal-complexing capacity;has a high metal complexing capacity;
Soil application of these compounds with Zn increased DM production and Zn uptake in canola and bread/durum wheat grown on calcareous Turkish and Australian soils;Turkish and Australian soils;
Rhamnolipid significantly (P≤ 0.05) increased Zn uptake by canola in ice-cold nutrient solutions despite reducing the (Zn2+) - Zn-rhamnolipid
h d i f f Z i li d i h M Zwas the predominant form of Zn in roots supplied with 5µM Zn-rhamnolipid.
PEI also dramatically increased Zn uptake by canola roots in solution culture and suggests very effect transmembrane transport
Both products show potential to improve micronutrient delivery in fluid fertilizersfertilizers
Acknowledgements