Phosphorus Chemistry in Soils
and
Response to Fertilizer and
Manures
April Leytem
USDA/ARS
The Phosphorus
Cycle
Crop
harvest
Animal
manures
and biosolids
Component
Inputs
Outputs
Atmospheric
deposition
Mineral
fertilizers
Plant
residues
Runoff and
erosion
Organic phosphorus
•Microbial
•Plant residue
•Humus
Plant
uptake
Soil solution
phosphorus
•HPO4-2
•H2PO4-1
Leaching
Primary
minerals
(apatite)
Dissolution
Precipitation
Mineral
surfaces
(clays, Fe and
Al oxides,
carbonates)
Secondary
compounds
(CaP, FeP, MnP, AlP)
PPI
Facts About Calcareous Soils
• Estimates of 800 million hectares of
calcareous soils worldwide
• Generally they are low in P due to
fairly insoluble Ca-P minerals
• The concentration of available P
continues to decrease over time
S oil P F ractions
M in eral
P ii
S o lu tio n
P ii & P oo
L ab ile
P ii & P oo
M ineral P > > > L abile P > > S olution -P
Phosphorus Sorption in Soils
S o rb e d P (m mo l P k g -1 )
100
Ex p e rim e n ta l D a ta
F re u n d lich
80
P re cip ita tio n
60
40
20
0
0
200
400
600
-1
E q u ilib riu m P (mg P L )
8 00
Calcite
Equilibrated
for 10
Days
0 ppm P
Calcite
Equilibrated
for 10
Days
10 ppm P
Calcite
Equilibrated
for 10
Days
50 ppm P
The quantity of P sorbed on calcite
depends largely on its surface area
Pure calcite has low surface area (1 to 2 m2/g)
Soil calcite has surface area ranging from 16 to
200 m2/g
(due to ongoing dissolution, reprecipitation, and
incorporation of impurities)
On pure calcite, sorption occurs on ~5% of the surface before
adsorption clusters serve as nuclei for Ca-P precipitation
Traditional Concepts
Adding P Fertilizer to High pH/ High Calcium Soils
• First few weeks, P initially precipitates as
MCP…. Then DCPD
• After 3 to 5 months, octacalcium phosphate
precipitates
• After 8 to 10 months, tricalcium phosphate
forms
• Long periods (years) hydroxyapatite minerals
form…
(mineral with lowest solubility controls P
concentration- while intermediates are unlikely
to persist)
(Fraction of Added P Still Extractable)
Fertilizer P Availability
Phosphorus Availability Decreases
Over Time
Average of 44% P sorption
between 30 and 180 days
following application
Incubation Period (days)
(Sharpley et al., 1989)
lbs P
Rate,lbs
PP
O55/A
/A
Rate,
P22O
Soil Test Calibration Studies
500
P ot a t o P R e c om m e nda t i ons
400
300
12% Lime
200
100
0 Lime
0
0
UI, 2001
10
20
STPC
30
40
Soil Test Correlation Studies
R elat ive Y ield R esp o nse, Po t at o es
Relative Yield, %
120
100
0 Lime
80
60
12% Lime
40
20
0
0
10
20
STPC
30
40
University of Idaho: Potato P Recommendations
take into account the free lime content of the soil
Majority of the soils had
a break-point at approx.
150 ppm.
Sorbed P (mmol P kg-1)
90
60
30
0
0
200
400
600
800
0
200
400
600
800
90
60
30
low P (<150 ppm), P
sorption with oxides, clay
surfaces, and organicallycomplexed metals (Fe &
Mn)
0
Equilibrium P (mg P L-1)
high P (>150 ppm),
precipitation reactions
Leytem and Westermann, 2003
Organically complexed Mn and Fe were the primary
factors controlling P sorption
Xt, mmol P kg-1
40
30
20
10
r2 = 0.86
0
0
300
600
900
1200
1500
NTA (Mn + Fe), mmol kg-1
Leytem and Westermann, 2003
Phosphorus Sorption in Soils
S o rb e d P (m mo l P k g -1 )
100
Ex p e rim e n ta l D a ta
F re u n d lich
80
P re cip ita tio n
60
40
20
0
0
200
400
600
-1
E q u ilib riu m P (mg P L )
8 00
How Can organically complexed
metals affect P adsorption?
P is complexed with OM through metal bridges?
PO4
• OM interferes with Ca-P and metal oxide
precipitation by coating the calcite surfaces?
Robbins and Westermann previously
showed that organic carbon enhanced
the solubility and extractability of
added P in calcareous soilsshowing that there are many
mechanisms regulating P sorption and
solubility
Organic Matter and P Interactions
Organic ligands affect P sorption- they compete
with orthoP for similar sites on the surface of
oxides.
Organic matter may also chelate metals and
prevent reactions between metals and P
How does this relate to Humic Acid additions?
Far West Fertilizer Meeting, 2004: “Never add P
fertilizer to a Calcareous soil without adding Humic
Acid with it”
University of Idaho experience with Humic
Acid (2003 report)
If Organically Complexed Metals
Control P Solubility, What
Happens When We Add Manure?
Myths About P and Manures
• Manure P is organic P
• Organic P is more soluble and more
readily leached than inorganic P
• Manure is a greater threat to water
quality than fertilizer P because it is
organic P
Some Typical Organic P
Compounds in Manures
OPO3H2
Organic P
OPO3H2
OPO3H2
H2O3PO
H2O3PO
OPO3H2
Phytic Acid
ATP
(monoester)
OH
Inorganic P
HO
P
OH
OH
O
Inorganic
Orthophosphate
HO
P
O
OH
O
P
O
Pyrophosphate
OH
P Sorption in Soils
500
-1
P Sorbed (mg P kg)
600
400
300
Phytic Acid
200
ATP
ADP
100
AMP
OrthoP
0
0
50
100
150
Equilibrium P (mg P mL-1)
200
Some Typical Organic P
Compounds in Manures
OPO3H2
Organic P
OPO3H2
OPO3H2
H2O3PO
H2O3PO
OPO3H2
Phytic Acid
ATP
(monoester)
OH
Inorganic P
HO
P
OH
OH
O
Inorganic
Orthophosphate
HO
P
O
OH
O
P
O
Pyrophosphate
OH
Manure P Composition
120%
OrthoP
Monoesters
PyroP
Phytic Acid
100%
80%
60%
40%
20%
0%
SL
SS-HP
DL
BS-grass
DC
PL
How does manure behave
as a fertilizer compared
to inorganic fertilizer?
Response
Soil Testin
P STP and Plant Growth
100
75
50
25
0
BS
DC
DL
POLYP
MAP
MCP
5
Dry matter (g)
RPE Olsen P
125
4
3
2
1
0
C
BS
MCP
DL
DC
MAP
POLYP
(Leytem & Westermann, 2005)
Plant P Uptake
P uptake (mg)
10
8
6
4
2
0
C
BS
MCP
DC
MAP
DL
POLYP
Although the soil test P increased less when
we applied manures….
The amount of P taken up by the plants was
greater for some manures than fertilizers
Phosphorus Uptake Efficiency
P Source
RPE
Olsen
RP
Efficiency
Uptake
Dairy Liquid
62.6
113.1
1.8
Beef Solid
26.5
59.5
2.24
Dairy Compost
49.0
149.9
3.05
MCP
100.0
100.0
1.0
MAP
85.3
145.0
1.69
Do these trends change in
the field?
Olsen P with Depth in Field Plots
Olsen P (ppm)
40
a
30
a
a
b
b
Control
Compost
Manure
Fertilizer
20
b
10
c
c
a
ab
ab
b
0
0-6"
6-12"
12-18"
Fertilizer and manure behave similarly in the topsoil, but fertilizer P
enriched STP in the subsurface compared to manure and compost
Runoff P from Field Plots
200
150
100
Control
Compost
Manure
Fertilizer
bc
ab
a
Fertilizer and manure had
similar runoff P while
compost and control were
lower but similar
c
50
0
250
Cumulative runoff P was
closely correlated with
the bicarbonate STP
Runoff P (mg)
Runoff P (mg)
250
200
150
100
2
r = 0.82
50
0
0
10
20
Olsen P (ppm)
30
40
P Uptake from Field Plots
Control
Compost
P uptake (kg)
30
Manure
a
a
a
Fertilizer
20
b
10
0
The addition of fertilizer, manure and compost increased the P
uptake by the crop, but they did not differ significantly
STP over 20 ppm does not require fertilizer addition
Is it really all just about
the P in manures or is
there something else going
on?
13C
NMR of WS-Carbon
Solid manures
dominated by
aromatic and
aliphatic compounds
(larger more stable)
Dairy Compost
150
100
50
0
Dairy Manure
150
Liquid manures
dominated by
carbonyl functional
groups (smaller more
reactive)
100
50
0
Dairy Liquid
150
100
C h e m ic a l s h ift (p p m )
50
0
-1
Olsen P (mg kg )
The Carbon in Manures Influences
the P solubility of the Soil
90
80
70
60
50
40
30
20
10
0
2
r = 0.90
0
50
100
C:P Ratio of Manures
150
Effect of Microbial P on WSP and Olsen P
WSP mg kg-1
60
40
r2 = 0.71***
20
0
Olsen P mg kg-1
60
r2 = 0.75***
40
20
0
0
20
40
Microbial P mg kg-1
60
P Release Over Growing Season From
Manure, Compost and Fertilizer
RPE PRS probes
50
40
compost
C:P = 15
manure
C:P = 45
fertilizer C:P = 0
30
20
10
0
0
2
4
6
8
Weeks
10
12
14
Summary
• Manure with similar P composition applied at same
total P rates
• Differences in P solubility dominated by the amount of
C added with the manure treatment
• Manures increase STP less than fertilizer treatments
but have a greater plant P uptake than fertilizer
Implications
• We need to consider the amount of C in
calcareous soils when determining P
sorption/availability
• When we make P risk assessments in calcareous
soils with manure incorporation, we need to
consider the effects of the C content and
composition of manures
• Microbial P has a large influence on soluble P and
this needs to be further explored
So Why the P Problems with Manures?

N:P ratios don’t match up




Overfeeding of P in animal operations



Crops want a ratio of about 5:1
Manure ratios are typically closer to 2:1
Therefore when applying manure on an N based rate
we are always over applying P
Low P availability of feeds in monogastrics leads to P
supplementation
Dairies traditionally overfeed P for insurance
Cost of transporting manures

Over application of manures on sites closest to manure
generation/storage
Northwest Irrigation and Soils
Research Laboratory
Kimberly, Idaho
USA