Phosphorus in manures and other organic products: What limits proper recycling of this resource in...

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

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P in organic products

• 4 - 40 mg P per kg dry matter

• Swine slurry > Urban sewage sludge > Beef/Cattle manure > Urban composts

• High variability (due to variability of animal diets, manure processes,…)

• Inorganic P 55-95% of total P


Morel et al., unpublished

0

10

20

30

40

50

60

70

1 2 3 4 5

P content (mgP/kg dry matter)

Swine slurry (34)Urban sewage

sludge (91)Urban

composts (23)Beef/cattle

manure (32)

*

*

*

*

Poultrymanure (5)


Organic fertilisers are as effective as mineral fertilisers for mid-term soil P fertility build-up


Shepherd and Withers, 1999

Ols

en

P (

mg

kg

-1)

So

il s

olu

tio

n P

(m

g k

g-1)

Poultry litter

Triple superphosphate (TSP)

Poultry litter + TSPP balance (kg P ha-1)


P, Tg.y-1

(year 2000)

P manure 17

P fertilizers 14

Total P input 31

P withdrawal 19

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)

Bouwman et al., PNAS, 2011


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

Nesme et al., 2014

1:1 line⇒ Full substitution hypothesis


What limits proper recycling of this P resource?


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


Source: Eurostat

Livestock density (LU ha-1) P manure (kg P ha-1) P mineral fertilisers (kg P ha-1)


Brittany

Centre

P budgets for two contrasted French agricultural regions


►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

Intensive animal farming region (Brittany)

Senthilkumar et al., 2012


► 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)

Intensive arable farming region (Centre)

Senthilkumar et al., 2012

.03Phosphorus 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

Morel et al., unpublished

0

5

10

15

1 2 3 4

N/P ratio of organic products

Beef/cattlemanure (11)

Swine slurry(55)

Poultry manure (5)

N/P ratio(15)

*

Crops (15)

N/P ratio

Leaf N/P ratio (TRY global database, Kattge et al., 2011)

N/P ratio of harvested organs (15 arable and forage crops)


Target yield Mg dry matter ha-1

N content in grain mg g-1 dry matter

P content in grain mg g-1 dry matter

N exports kg N ha-1

P exports kg P ha-1

Amount of cattle manure required to compensate N exports kg DM ha-1

Amount of P supplied kg P ha-1

N budget kg N ha-1

P budget kg P ha-1

8 20 3 160 24 6400 44.8 0 +20.8

Example of a N-P budget for wheat fertilised with cattle manure


3. Questions remain about the ability of P from organic fertilizers to match crop requirements in time

Ex of the early « critical stage » on maize

Mineral P « starter fertilisers » are often used by farmers to supply high P concentrations close to the roots during this critical stage

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…)

Mollier, 2013

P d

eman

d (m

g P

km-

1 d-

1)


Classical approach: Standardized plant P tests

100

controlPMFP

controlPOFP%) (in Efficiency Relative

uptake uptake

uptake uptake

No P added(control)

Organic fertilizer(OF)

Same amount of P added as soluble

mineral fertilizer (MF)

+ POF + PMF0 P

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.

4. Methodological issues and uncertainties in P fertilizing value assessment


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


Reliable studies show that the short term P fertilising value of animal manures is generally high

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

Relative efficiency (% of soluble mineral fertiliser)

Organic sources Range

Pig manure 84-102%

Beef manure 68-111%

Poultry manure 43-88%


Summary and Conclusion• Organic fertilisers are as effective as mineral fertilisers for mid-

term 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


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


Thank you for your attention



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


More reliable approaches are based on labelling techniques

(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)

(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 %)

Control (0P)

100MF

OF

Pdff

Pdff%) (in Efficiency Relative

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