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Phosphorus in manures and other organic products: What limits proper recycling of this resource in agriculture? Sylvain PELLERIN, Christian MOREL, Thomas.

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Presentation on theme: "Phosphorus in manures and other organic products: What limits proper recycling of this resource in agriculture? Sylvain PELLERIN, Christian MOREL, Thomas."— Presentation transcript:

1 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’AUTEUR03 / 12 / 2013

2 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

3 P in organic products 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Inorganic P  55-95% of total P Phosphorus in manures and other organic products 02 Sept 2014 Morel et al., unpublished

4 Organic fertilisers are as effective as mineral fertilisers for mid-term soil P fertility build-up Phosphorus in manures and other organic products 02 Sept 2014 Shepherd and Withers, 1999 Olsen P (mg kg -1 ) Soil solution P (mg kg -1 )  Poultry litter  Triple superphosphate (TSP)  Poultry litter + TSP P balance (kg P ha -1 )

5 Phosphorus in manures and other organic products 02 Sept 2014 P, Tg.y -1 (year 2000) P manure17 P fertilizers14 Total P input31 P withdrawal19 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

6 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 km 2 Nesme et al., :1 line ⇒ Full substitution hypothesis

7 Phosphorus in manures and other organic products 02 Sept 2014 What limits proper recycling of this P resource?

8 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 Phosphorus in manures and other organic products 02 Sept 2014 Source: Eurostat Livestock density (LU ha -1 )P manure (kg P ha -1 ) P mineral fertilisers (kg P ha -1 )

9 Phosphorus in manures and other organic products 02 Sept 2014 Brittany Centre P budgets for two contrasted French agricultural regions

10 Phosphorus in manures and other organic products 02 Sept 2014 ►The soil P budget is highly positive ( 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

11 Phosphorus in manures and other organic products 02 Sept 2014 ► 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

12 .03 Phosphorus in manures and other organic products 02 Sept 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 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)

13 .03 Phosphorus in manures and other organic products 02 Sept 2014 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 compens ate 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 Example of a N-P budget for wheat fertilised with cattle manure

14 .03 Phosphorus in manures and other organic products 02 Sept 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 demand (mg P km -1 d -1 )

15 .03 Phosphorus in manures and other organic products 02 Sept 2014 Classical approach: Standardized plant P tests + P OF + P MF 0 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 (P uptake control) ⇒ Standardized plant test using labelling techniques ( 32 P or 33 P) are more reliable, but require dedicated laboratory facilities. 4. Methodological issues and uncertainties in P fertilizing value assessment

16 .03 Phosphorus in manures and other organic products 02 Sept 2014 Fertilising value (% soluble mineral fertiliser) LabellingNo labelling Farmyard manure68207 Poultry manure43407 Soluble mineral fertiliser 100 Mohanty et al., 2006

17 .03 Phosphorus in manures and other organic products 02 Sept 2014 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 sourcesRange Pig manure % Beef manure % Poultry manure 43-88%

18 .03 Phosphorus in manures and other organic products 02 Sept 2014 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

19 .03 Phosphorus in manures and other organic products 02 Sept 2014 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

20 .03 Phosphorus in manures and other organic products 02 Sept 2014 Thank you for your attention

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22 .03 Phosphorus in manures and other organic products 02 Sept 2014 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

23 .03 Phosphorus in manures and other organic products 02 Sept 2014 More reliable approaches are based on labelling techniques (1) Isotopic labelling of plant-available soil P with 32 P-PO 4 or 33 PO 4 (2) 50 mg P kg -1 soil applied as:  Organic fertiliser (OF)  or Triplesuperphosphate (MF) (3) Determination of the 31 P and 32 P 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)


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