sustainable phosphorus use in agroecosystems: a story of global imbalance and resource recycling...

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 messages1. 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

Moderate P fertilisation

No P fertilisationHigh 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

• With N addition, this would save 29 millions ha from cropland expansion and provide food for +200 millions people

(van der Velde et al., 2013)

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

Imports Domestic

PUE

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Trade improves P resource use efficiency globally

• 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

PUE = P in harvested crops /

P fertiliser applied

2007

n=8

(From Schipanski and Bennett, 2011)

But at regional scale, P budgeting exhibits major imbalances across the world croplands

(MacDonald et al., 2011)

•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

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

Labile PNat

Stable PNat

Labile PAnt

Stable PAnt

Livestock

Fertilisers

Soil P pools

Food

Feed Manure

By 2010, ~80% of France's soil P originated from mineral fertiliser!

(Ringeval et al., 2014)

Anthropogenic signature of French

soil P pools

LP: Labile PSP: Stable P

Years

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

Chickens

Pigs

(Robinson et al., 2014)

Crop P fertiliser use efficiency = 66%

Livestock feed P use efficiency = 8%

Livestock feed P100 g

Livestock product P8 g

92 g

Fertiliser P100 g Crop P

66 g

34 g

Manure P surpluses also result from the low P use efficiency of livestock production

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

• 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)

Pig density in France in 2010

Urban areaArable landPermanent cropGrasslandMixed cropsForestNatural pasturePeatlandWater

Legend

Livestock district1.2 LU/ha(n=21)

Arable district0.2 LU/ha(n=25)

Mixed district0.6 LU/ha (n=17)

Crop / livestock segregation limits the P resource recycling

Specialisedarable

Mixed Specialisedlivestock

Surveyed farm Other farm Material flow Cycling pattern

(Nowak et al., subm)

Local autonomy (%)

Cycling index (%)

Specialised arable 39 0

Mixed 52 20

Specialised livestock 13 0

Material exchanges are more important in mixed districts

Crop / livestock segregation structures P flows at regional scale

Centre region•Livestock density: 0.3 LU/ha•Arable crops: 65% of UAA

• 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)

Other inputs1.9

Fertilizer12.9

Erosion1.8

Animal products1

Feed2.3

Crop products13.4

Fodder2.8

Crop uptake

20.2

Crop residue4

Animal Excretion

4.2

Animals 5.1 (-0.6)

Crops20.2 (0)

Soils23.1 (1.1)

Brittany region•Livestock density: 2.1 LU/ha•Arable crops: 6% of UAA

(Gaigné et al., 2012)

Dairy cows

PoultryPigs

• 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)

Other inputs2

Fertilizer7.9

Erosion1.7

Animal products12.3

Feed28.9

Crop products7.1

Fodder23.5

Crop uptake

21.8

Crop residue3.3

Animal Excretion

29.1

Animals 40.2 (-1.2)

Crops21.8 (0)

Soils42.3 (18.9)

Crop / livestock segregation drives mineral P fertiliser use in arable regions

(Nesme et al., subm)

Proxy of crop / livestock segregationVariation coefficient of the stocking rate at department scale (%)

Similar patterns of soil P accumulation in livestock regions exist worldwide…

(Gerber et al., 2005)

Poultry density Soil P balance

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)

Years (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)

P flows among world regions in 2011 (in Tg P/yr)

Trade P flows interconnect world

regions

(Nesme et al., in prep)

Conclusion

Take home message1. 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 crop-

livestock 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

(from Withers et al., subm)

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.)