Phosphorus in manures and other organic
products:
What limits proper recycling of this
resource in agriculture?
Sylvain PELLERIN, Christian MOREL, Thomas
NESME, Bruno RINGEVAL
NOM DE L’AUTEUR
03 / 12 / 2013
Outline
- Background
- Four barriers / issues for optimal recycling of P from
manures
- Geographical segregation between livestock and crop
production systems
- Inadequate N/P ratio
- Mismatch with temporal crop requirements
- Uncertainties in P fertilizing value assessment
- Conclusion
Phosphorus in manures and other organic products
02 Sept 2014
P in organic products
• 4 - 40 mg P per kg dry matter
70
• Swine slurry > Urban sewage
sludge > Beef/Cattle manure >
Urban composts
• High variability (due to
variability of animal diets,
manure processes,…)
60
P content (mgP/kg dry matter)
*
50
40
30
*
*
20
*
10
0
• Inorganic P  55-95% of total P
1 (34)
Swine slurry
Urban sewage Beef/cattle
2
3
sludge (91)
manure (32)
Urban
4
composts (23)
Morel et al., unpublished
Phosphorus in manures and other organic products
02 Sept 2014

Poultry litter

Triple superphosphate (TSP)

Poultry litter + TSP
Olsen P (mg kg-1)
Soil solution P (mg kg-1)
Organic fertilisers
are as effective as
mineral fertilisers
for mid-term soil P
fertility build-up
P balance (kg P ha-1)
Shepherd and Withers, 1999
Phosphorus in manures and other organic products
02 Sept 2014
At the global scale, the
amount of P in manures
represents 17 Tg P.y-1
(more than P in mineral
fertilizers)
But P budget calculations
suggest a non-optimal use
of this resource
⇒ Assuming an « optimal » manure
P recycling, the need for additional
mineral P would be much lower
than actually observed (2 instead
of 14 Tg P y-1)
P, Tg.y-1
(year 2000)
P manure
17
P fertilizers
14
Total P input
31
P withdrawal
19
Bouwman et al., PNAS, 2011
Phosphorus in manures and other organic products
02 Sept 2014
Only partial substitution of mineral P by
P from organic products is also
observed at local scale
Ex of France: 76 agricultural districts, approx. 5000 km2
1:1 line
⇒ Full
substitution
hypothesis
Nesme et al., 2014
Phosphorus in manures and other organic products
02 Sept 2014
What limits proper recycling
of this P resource?
Phosphorus in manures and other organic products
02 Sept 2014
1. Farm specialisation and increasing geographical
segregation between livestock and crop production
systems
•
•
hamper the use of manure as a P fertilizer source in specialised arable
farming regions
are responsible for excess P in animal farming regions
Livestock density (LU ha-1)
P manure (kg P ha-1)
P mineral fertilisers (kg P ha-1)
Source: Eurostat
Phosphorus in manures and other organic products
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P budgets for two contrasted French
agricultural regions
Brittany
Centre
Phosphorus in manures and other organic products
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Intensive animal farming
region (Brittany)
►The soil P budget is highly
positive (+ 18.9 kg P ha-1 yr-1)
►High P inflows due to feed
imports (28.9 kg P ha-1 yr-1)
and fertiliser use (7.9 kg P ha-1
yr-1)
►Even without P fertiliser use,
the soil P budget would remain
positive
Phosphorus in manures and other organic products
Senthilkumar et al., 2012
02 Sept 2014
Intensive arable farming
region (Centre)
► The soil P budget is close
to the equilibrium (+1.1 kg P
ha-1 yr-1)
► However, crop exports are
supported by massive
mineral P fertiliser imports
(+12.9 kg P ha-1 yr-1)
Senthilkumar et al., 2012
Phosphorus in manures and other organic products
02 Sept 2014
2. Organic fertilising materials have low N/P ratio. If used
for N targeted fertilisation they lead to soil P excess
⇒ this P accumulates in soils
⇒ and is no longer available as a substitute for mineral P elsewhere
N/P ratio
15
N/P ratio of organic products
Leaf N/P ratio
(TRY global database,
Kattge et al., 2011)
10
5
0
*
N/P ratio of harvested
organs (15 arable and
forage crops)
Swine slurry Poultry manure Beef/cattle
1
2
3 (11)
manure
(5)
(55)
N/P ratio
Crops
4 (15)
(15)
Phosphorus in manures and other organic products
Morel et al., unpublished
.03
02 Sept 2014
Example of a N-P budget for wheat
fertilised with cattle manure
Target
yield
Mg dry
matter
ha-1
N
P
N
P
Amount
content content exports exports of cattle
in grain in grain kg N ha-1 kg P ha-1 manure
required
mg g-1
mg g-1
dry
dry
to
matter
matter
compens
ate N
exports
Amount N
P
of P
budget budget
supplied kg N ha-1 kg P ha-1
kg P ha-1
kg DM ha-1
8
20
3
160
24
6400
44.8
Phosphorus in manures and other organic products
0
+20.8
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02 Sept 2014
Ex of the early « critical stage » on maize
P demand (mg P km-1 d-1)
3. Questions remain about the
ability of P from organic
fertilizers to match crop
requirements in time
Mineral P « starter fertilisers » are often used
by farmers to supply high P concentrations
close to the roots during this critical stage
Mollier, 2013
This questions the ability of organic products
to act as an effective substitute to soluble
mineral fertilisers in this context
Moreover, scheduling applications of organic
fertilisers is often constrained by practical
aspects (trafficability, etc…)
Phosphorus in manures and other organic products
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02 Sept 2014
4. Methodological issues
and uncertainties in P
fertilizing value assessment
Classical approach:
Standardized plant P tests
0P
No P added
(control)
+ POF
Organic fertilizer
(OF)
+ PMF
Same amount of P
added as soluble
mineral fertilizer (MF)
Puptake OF  Puptake control
Relative Efficiency (in %) 
100
Puptake MF  Puptake control
This approach may be misleading because it assumes that the amount of P
taken up by plants originating from the soil is not modified by experimental
treatments (Puptakecontrol)
⇒ Standardized plant test using labelling techniques (32P or 33P)
are more reliable, but require dedicated laboratory facilities.
Phosphorus in manures and other organic products
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Fertilising value (% soluble mineral
fertiliser)
Labelling
No labelling
Farmyard manure
68
207
Poultry manure
43
407
Soluble mineral
fertiliser
100
100
Mohanty et al., 2006
Phosphorus in manures and other organic products
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02 Sept 2014
Reliable studies show that the short term P fertilising value of
animal manures is generally high
Relative efficiency (% of soluble mineral fertiliser)
Organic sources
Range
Pig manure
84-102%
Beef manure
68-111%
Poultry manure
43-88%
But it remains that the short-term dynamics of P after manure application
may be affected by many factors (e.g. P immobilisation by microbial biomass
if high C/P ratio)
⇒ Standardized plant tests are useful tools to rank organic products in
standardized conditions
⇒ We need a better understanding of the short term fate of P after
manure application in field conditions
Phosphorus in manures and other organic products
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Summary and Conclusion
• Organic fertilisers are as effective as mineral fertilisers for midterm soil P fertility build-up.
• Reliable results suggest that short term P availability in manures is
generally high, although variable
• Optimal substitution of mineral P by P from organic products is
limited by
– the increasing geographical segregation of animal and crop farming
regions,
– inadequate N/P ratio,
– Questions about the ability of P from organic fertilizers to match crop
requirements in time
– Uncertainties in P fertilizing value assessment
• Practical constraints (storage, handling, trafficability) may also act
as barrier
Phosphorus in manures and other organic products
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Summary and Conclusion
• Innovations are needed
– To reconnect livestock and crop production
• Regulation on maximum livestock densities?
• Exchange markets of manures
• Technologies to reduce volumes and transportation expenses (granular,
pellets,…)
• Recovery options (struvite precipitation,…)
– to get a N:P ratio better adapted to plant requirements
• Reduce P content in manure by re-aligning P diets on animal requirements,…
• Increase N content by reducing N gaseous losses
• A research effort is still needed to better understand and predict
short term P release and availability for plants after application
Phosphorus in manures and other organic products
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Thank you for your attention
Phosphorus in manures and other organic products
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Today, the lack of robust references about short term P
fertilising value of organic products may partly explain
why farmers do not fully take into account manure
application as mineral dose diminishing factors
1:1 line
⇒ Full
substitution
hypothesis
Phosphorus in manures and other organic products
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02 Sept 2014
More reliable approaches are based on labelling
techniques
(3) Determination of the 31P
and 32P quantities in aerial
parts
(4) Calculation of the fraction of the P
taken up by plants which derives from
the fertilizer (Pdff, in %)
PdffOF
Relative Efficiency (in %) 
100
PdffMF
Control
(0P)
(1) Isotopic labelling of plant-available
soil P with 32P-PO4 or 33PO4
(2) 50 mg P kg -1 soil applied
as:
Organic fertiliser (OF)
or Triplesuperphosphate (MF)
Phosphorus in manures and other organic products
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02 Sept 2014