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 Moderate P fertilisation No P fertilisation High 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-21 st century – Depletion of phosphate resources before mid-22 nd 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 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 , 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 P SP: 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 P 100 g Livestock product P 8 g 92 g Fertiliser P 100 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 area Arable land Permanent crop Grassland Mixed crops Forest Natural pasture Peatland Water Legend Livestock district 1.2 LU/ha (n=21) Arable district 0.2 LU/ha (n=25) Mixed district 0.6 LU/ha (n=17) Crop / livestock segregation limits the P resource recycling

Specialised arable Mixed Specialised livestock Surveyed farmOther farmMaterial flowCycling pattern (Nowak et al., subm) Local autonomy (%) Cycling index (%) Specialised arable390 Mixed5220 Specialised livestock130 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 inputs 1.9 Fertilizer 12.9 Erosion 1.8 Animal products 1 Feed 2.3 Crop products 13.4 Fodder 2.8 Crop uptake 20.2 Crop residue 4 Animal Excretion 4.2 Animals 5.1 (-0.6) Crops 20.2 (0) Soils 23.1 (1.1)

Brittany region Livestock density: 2.1 LU/ha Arable crops: 6% of UAA (Gaigné et al., 2012) Dairy cows Poultry Pigs

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 inputs 2 Fertilizer 7.9 Erosion 1.7 Animal products 12.3 Feed 28.9 Crop products 7.1 Fodder 23.5 Crop uptake 21.8 Crop residue 3.3 Animal Excretion 29.1 Animals 40.2 (-1.2) Crops 21.8 (0) Soils 42.3 (18.9)

Crop / livestock segregation drives mineral P fertiliser use in arable regions (Nesme et al., subm) Proxy of crop / livestock segregation Variation 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 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 crop- livestock farming systems… with synergies for other environmental issues (e.g., biodiversity, soil erosion, animal diseases)

Thanks for your attention!

A 5R strategy should be deployed and adapted to the different P contexts R ealign P inputs Match P inputs to P requirements Use residual soil P R educe P losses to water Minimise P losses in runoff R ecycle P in manure Integrate crop and livestock systems R ecover P in waste Produce P fertiliser substitute R edefine P in food chain Influence dietary choice (from Withers et al., subm)

Struvite production? Which sources for struvite production at the global scale? – Total annual P production in manure = 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 = 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.)