Sustainable phosphorus use in agroecosystems:
A story of global imbalance and resource recycling
Thomas NESME & Elena BENNETT
5th Phosphorus in Soils and Plants congress,
August 2014
Key messages
1. At the global scale, trade of agricultural products
improves P resource use efficiency
2. But at regional scale, current P management in
agroecosystems exhibits major imbalances
3. These imbalances are often due to crop and livestock
segregation
4. This segregation drives major P flows and P resource
displacement
Phosphorus is a key factor for crop
production
High P fertilisation
No P fertilisation
Moderate P fertilisation
At the global scale, a significant fraction of
croplands is nutrient limited
Maize
Wheat
(Mueller et al., 2012)
In heavily P limited soils, small addition of
P can boost crop yields
• Small addition of 10 kg
P/ha/yr could increase
maize yields by 12% in
South America and 26%
in Africa
(van der Velde et al., 2013)
• With N addition, this
would save 29 millions
ha from cropland
expansion and provide
food for +200 millions
people
P losses from agricultural lands trigger algal
blooms, hypoxia and water eutrophication
'Dead zones' are observed worldwide and
their number has doubled since the 1960's
(Diaz and Rosenberg., 2008)
Toward rock phosphate depletion?
?
(Cordell et al., 2009)
Although controversies exist, reports converge to
– Peak in global P extraction by mid-21st century
– Depletion of phosphate resources before mid-22nd century
– And, as a result, to predicted increase of mineral P fertiliser price
(Peñuelas et al., 2013)
As a consequence, there is a need to:
– Draw a picture of the current management of P
resources in agroecosystems at the global scale
– Understand the effects of crop / livestock
segregation on P resource use
– Assess the effects of agricultural product trade
Trade of agricultural products has increased
dramatically over the last decades
• International trade
represents nowadays
~20% of global crop
production
• Trade connects
countries with different
P use practices
Trade improves P resource use efficiency
globally
PUE =
P in harvested crops /
P fertiliser applied
1.2
2007
1.0
n=8
PUE
0.8
0.6
0.4
0.2
• Crop imports are often
sourced from countries
with higher PUE
• At the global scale,
trade of crop products
may improve the use
efficiency of limited P
fertiliser resources
0.0
Imports
Domestic
(From Schipanski and Bennett, 2011)
But at regional scale, P budgeting exhibits major
imbalances across the world croplands
•At the global scale, annual inputs of P fertilizer (14 Tg P) and
manure (10 Tg P) exceed P removal by crops (12 Tg P), resulting
in a 12 Tg P surplus in croplands
•10% of the croplands receive over 50% of the global use of
both fertiliser and manure
•However, 15% of the cropland area has major deficits while
35% has major P surplus
(MacDonald et al., 2011)
Cumulative imbalances led to major
residual soil P
• At the global scale, from
1965-2007, half of the
total applied P (550 kg
P/ha) was taken up by
crops (225 kg P/ha)
• This resulted in massive
accumulation of
residual P in highly
fertilised soils (e.g. in
Brittany in France)
(Lemercier et al., 2008)
Residual soil P could help to reduce
fertiliser P demand
• In regions with strong P
accumulation, residual soil P
could play a critical role to
meet crop requirements
• In those regions, P
application could be
reduced
• Innovations are needed to
better mine this residual
soil P (e.g., intercropping,
enhanced microbial activity)
(Sattari et al., 2012)
• In contrast, in regions
with limited
accumulated past P
supply, residual soil P
will play a small role
• In those regions,
additional inputs will
be required to meet
crop requirements
(Sattari et al., 2012)
In regions with massive P supply, soil P
is mainly anthropogenic
• Massive use of P fertiliser has increased the
contribution of anthropogenic P (i.e. inherited from
mineral fertiliser) vs natural origin of soil P stocks
• Case-study: modelling of the natural vs anthropogenic
soil P pools for France, accounting for mineral P
fertiliser use and crop-livestock recycling loop, from
1948 to 2010
Livestock
Feed
Food
Fertilisers
Soil P pools
Labile
PNat
Stable
PNat
Labile
PAnt
Stable
PAnt
Manure
By 2010, ~80% of France's soil P originated
from mineral fertiliser!
Anthropogenic
signature of French
soil P pools
LP: Labile P
SP: Stable P
Years
(Ringeval et al., 2014)
The uneven distribution of mineral fertilisers
explains part of the soil P imbalances
Fertiliser inputs exceed crop P requirements in 45% of
the world croplands
(Potter et al., 2010)
But manure supply also drives soil P
imbalances
Manure inputs exceed crop P requirements in 25% of
the world croplands
(Potter et al., 2010)
Manure P surpluses result from the uneven
distribution of livestock animals
Cattle
Pigs
Chickens
(Robinson et al., 2014)
Manure P surpluses also result from the
low P use efficiency of livestock production
Crop P fertiliser use efficiency = 66%
Fertiliser P
100 g
Crop P
66 g
34 g
Livestock feed P use efficiency = 8%
Livestock
feed P
100 g
Livestock
product P
8g
92 g
Crop and livestock segregation is a key
driver of soil P imbalances
• Livestock production systems are
increasingly specialised and
spatially segregated from arable
production systems
Pig density in France in 2010
• This segregation generates
– Large feed imports and soil P
surplus in regions of livestock
production
– Limited manure supply and
large mineral P fertiliser use in
regions of arable production
(Gaigné et al., 2012)
Crop / livestock segregation
limits the P resource recycling
Livestock district
1.2 LU/ha
(n=21)
Mixed district
0.6 LU/ha
(n=17)
Legend
Urban area
Arable land
Permanent crop
Grassland
Mixed crops
Forest
Natural pasture
Peatland
Water
Arable district
0.2 LU/ha
(n=25)
Material exchanges are more important in
mixed districts
Specialised
arable
Surveyed farm
Specialised
livestock
Mixed
Other farm
Material flow
Cycling pattern
Local autonomy
(%)
Cycling index
(%)
Specialised arable
39
0
Mixed
52
20
Specialised livestock
13
0
(Nowak et al., subm)
Crop / livestock segregation structures
P flows at regional scale
Centre region
• Livestock density: 0.3 LU/ha
• Arable crops: 65% of UAA
Feed
2.3
Fodder
2.8
Crop products
13.4
Crops
20.2 (0)
Animals
5.1 (-0.6)
Crop residue
4
Animal products
1
Animal
Excretion
4.2
Soils
23.1 (1.1)
Erosion
1.8
Crop uptake
20.2
Fertilizer
12.9
Other inputs
1.9
• Balanced soil P inputs and outputs (+1 kg P/ha/yr)
• Large use of mineral P fertiliser (13 kg P/ha/yr)
(Senthilkumar et al., 2012)
Brittany region
• Livestock density: 2.1 LU/ha
• Arable crops: 6% of UAA
Dairy cows
Poultry
Pigs
(Gaigné et al., 2012)
Feed
28.9
Fodder
23.5
Crop products
7.1
Animal products
12.3
Animals
40.2 (-1.2)
Crop residue
3.3
Animal
Excretion
29.1
Soils
42.3 (18.9)
Crops
21.8 (0)
Erosion
1.7
Crop uptake
21.8
Fertilizer
7.9
Other inputs
2
• Soil inputs >> outputs  highly positive soil P budget (+ 19 kg
P/ha/yr)
• Animal feed represents 75% of total P inputs. Even without mineral
P fertiliser, the soil P budget would remain highly positive
• Animal manure spreading on soils can hardly be qualified as P
recycling
(Senthilkumar et al., 2012)
Crop / livestock segregation drives
mineral P fertiliser use in arable regions
Proxy of crop / livestock segregation
Variation coefficient of the stocking rate at department scale (%)
(Nesme et al., subm)
Similar patterns of soil P accumulation
in livestock regions exist worldwide…
Poultry density
Soil P balance
(Gerber et al., 2005)
The crop / livestock segregation drives
global P resource displacement
International food/feed trade among countries
increased dramatically in the past decades
– P trade flows increased from 0.4 Tg in 1961 to 3.0
Tg in 2011 (x7 increase)
– In 2011, 20% of the global crop production was
traded
– In 2011, P trade flows were equivalent to 17% of
global P fertiliser use
International P flows are driven by
soybean and cereal trade
Trade P flows
(Tg P/yr)
3.50
Soybeans
3.00
Pulses (other than soybeans)
2.50
Other
2.00
Fruits and vegetables
1.50
Forage
1.00
Cereals
0.50
Cakes (other than soybean
cakes)
Animal products
0.00
1961
1968
1975
1982
1989
Years
1996
2003
2010
(Nesme et al., in prep)
For some countries, P imports through trade
provide large amounts of P resources
P import through trade as % of domestic P fertiliser use
(Nesme et al., in prep)
Trade P flows
interconnect world
regions
P flows among
world regions in
2011 (in Tg P/yr)
(Nesme et al., in prep)
Conclusion
Take home message
1. At the global scale, trade of agricultural products
improves P resource use efficiency
2. But at regional scale, current P management in
agroecosystems exhibits major imbalances
3. These imbalances are often due to crop and livestock
segregation
4. This segregation drives major P resource
displacement at the global scale
Solutions?
• The multi-faceted P issues call for solutions
adapted to different contexts
– Increased mineral P inputs in soils with low P status
– Reduced P losses to water bodies from soils with high
P status
– Increased P resource recycling everywhere
• The global interconnections and regional
inefficiencies call for integrated approaches
across the world
However, in the long term P resource recycling
in agroecosystems should be a priority
A range of different options should be explored
– P mining from residual soil P
– Reduced P losses from agricultural soils
– P recovery from rich streams (e.g. struvite production from
urban wastes)
– Agriculture redesign towards more integrated croplivestock farming systems… with synergies for other
environmental issues (e.g., biodiversity, soil erosion,
animal diseases)
Thanks for your attention!
thomas.nesme@agro-bordeaux.fr
A 5R strategy should be deployed and
adapted to the different P contexts
Realign P
inputs
Reduce P
losses to
water
Recycle P in
• Match P inputs to P requirements
• Use residual soil P
• Minimise P losses in runoff
• Integrate crop and livestock systems
manure
Recover P in
• Produce P fertiliser substitute
waste
Redefine P in
food chain
(from Withers et al., subm)
• Influence dietary choice
Struvite production?
• Which sources for struvite production at the global scale?
– Total annual P production in manure = 20-30 Mt P/yr (of which a large
fraction is probably already recycled)
– Total annual P production in waste-water = 3-5 Mt P/yr (of which 30-40%
is already recycled to Ag soils)
– Compared to total annual use of mineral P fertiliser = 15-20 Mt/yr
• Some technical issues to be overcome
– Organic effluents have low (<10 mg P/L) and variable P content
– Struvite production exhibits high energy and economic costs
• Struvite production costs: 6800 US $/t P
• Mineral P fertiliser price: 2000 US $/t P
– Most countries lack of proper regulation framework
• Struvite production could solve part of the P problem but does not
account for the other consequences of crop/livestock segregation
(e.g., short crop rotations, pest and disease propagation, etc.)