Phosphorus recycling is a emerging problem in organic farming due to deterioration of rock phosphate sources from earth. There is a need for usage of alternative sources for P requirement by knowing their environmental impacts.

1. DOCTORAL SEMINAR
PHOSPHORUS RECYCLING: THE DRIVER OF SUSTAINABLE ORGANIC
FARMING
Department of Soil Science
Dr. Rajendra Prasad Central Agricultural University,
Pusa, Samastipur
Speaker
Ms. Rajeswari Das
Ph.D. Scholar (Soil Science)

2. PRESENTATION INCLUDES
P DEFICIT BUDGETS OF ORGANIC FARMING
RECYCLED P FERTILISERS
CONSRAINTS IN RECYCLED P FERTILISERS
APPLICATION
IMPROVED P RECYLING FOR SUSTAINABLE
ORGANIC FARMING
INFERENCES DRAWN

3. INTRODUCTION
Organic farming is a production system which avoids or largely excludes the use of synthetically
compounded fertilizers, pesticides, growth regulators, genetically modified organisms and livestock food
additives.
In 2018, 2.9 million organic producers were reported, which is 5 percent more than in 2016. India
continues to be the country with the highest number of producers (835,200), followed by Uganda
(210,352), and Mexico (210,000) (IFOAM, 2018).
Although our country holds highest number of producers but merely with 0.4 percent of total agricultural
land under organic cultivation. Achieving more productivity from this ample land can exhaust the
nutrient reserve of soil unless until there is sufficient provision of nutrient recycling.
Phosphorus which plays vital role in photosynthesis, respiration, energy storage and transfer, cell division,
cell enlargement and several other processes in plants is the major limiting nutrient in soil.
Organic production guidelines ban the use of highly soluble, manufactured P fertilisers and, thus,
recommend the cycling of wastes and by-products of plant and animal production (e.g., livestock
manures, compost) and low soluble mineral fertilizers (e.g., rock phosphates).

4. Contd…
Phosphorus—The Predicament of Organic Farming
➢ Today on many sites organic farming might neglect phosphorus (P) fertilization due to
soil reserves build up by P fertilization of former farming systems.
➢ Additionally organic farming has restricted itself to the use of non-solubilised rock
phosphate as mineral fertilizer source that only has limited plant availability on
agricultural soils with adequate pH (Acidic pH).
➢ In farms located on P-rich soils, P exported from fields by agricultural products may
exceed P input by fertilizers for quite some time without yield reductions, while in other
situations low P availability may limit crop and animal production.
➢ Also recycling of P from the food chain back to organic agriculture is not consequently
realised. These predicaments of organic farming endanger its future sustainability.

5. As budget helps to assess the sustainability of a given cropping system in terms of increase or decrease of the
soil P reserves it is important and essential criteria to be considered in practical guidelines for P management
drawn up for farmers and their advisors.
At the current rate of extraction, it is likely that global phosphate rock reserves will be exhausted within the
next few centuries (Desmidt et al., 2015; Elser, 2012), and that the rate of production of economically available
P reserves will peak between 2030 and 2040, after which demand would likely exceed supply (Schroder et al.,
2011).
Soil persists as a temporal reservoir for phosphorus (P) in plant production, but only a relatively small fraction
of total soil P is available for direct plant or microbial uptake (Annaheim et al. 2013).
Many organic farms tolerate P budget deficits not knowing when soil reserves will be depleted (Gosling and
Shepherd 2005).
Under conditions of long-term negative P budget in organic farming, the decline in readily available soil P
pools would be less pronounced in a dairy system than in a stockless system (arable land). It is believed this was
due to the manure backflow to fields, the higher percentages of forage legumes, and longer soil cover during
the year in the dairy systems.
Long-term deficit phosphorus budgets in organic crop rotations depleting plant-
available phosphorus from soil

6. Drivers of sustainable organic farming
Site specific analysis of plant
available P
Analyses of field and farm
P-budgets
Soluble P sources (Recycled
P fertilisers)
Meeting future P
fertilization demands of
organic farming

7. RECYCLED PHOSPHORUS FERTILISERS (RPFs)
The importance of raw materials for phosphorus (P) fertilizer production is expected to increase in the future
due to resource depletion, supply risks, and heavy metal contamination of fossil phosphate resources.
Municipal wastewater is a promising source for P recovery. In Germany for instance, it contains almost 50% of
the total amount of P that is currently applied as mineral fertilizer.
Several procedures have been developed to recover and re-use P resulting in a growing number of recycling
fertilizers that are currently not regulated in terms of fertilizer efficiency.
The reuse of phosphorus (P) from any organic source should follow the principles of International Federation of
Organic Agriculture Movements (IFOAM).
Principle of ecology
(Production is to be based on
ecological processes and
recycling)
Principle of care
(Utilization of organic waste free
from harmful compounds)

8. P DEFICIT BUDGETS OF ORGANIC FARMS
P requirement of
crops in organic
farming
Plant available P

9. Table 1. P balances (kg ha−1 P) of grassland and arable land of two organic dairy farming systems
(29.8 % grassland) fertilizing with livestock slurry without P import (P circle) or biogas manure with
P import by external substrates (digestion of all field residues, manure and external plant silage: P
import of 5.3 kg ha−1)
Moller. K. , 2009
Eur. J. Agron.
aP import via mineral feed 0.26 kg ha−1
Grass land (1 ha) Arable land (1 ha)
Export Return Balance Export Return Balance
P circle a -13.8 +10.9 -2.9 -17.0 +14.8 -2.3
P import a -16.2 +17.9 +1.8 -26.0 +29.6 +3.6

10. (n = 24 per year and crop rotation,
sampling depth: 0–30 cm, 2001,
2003–2013) and on grassland (n =
8 per year, sampling depth: 0–10
cm, 2003–2013) and acceptable
lower threshold.
A declining trend is visible in all
three systems. Error bars indicate
the 95% confidence interval of the
LS-means. Regression equations:
Grassland:y = −3.177x + 172.48,
adj. r2 = 0.30, p = 0.046, Stockless
arable: y = −1.763x + 91.5, adj. r2
= 0.66, p = 0.001, Dairy arable: y =
−1.415x + 80.54, adj. r2 = 0.50, p =
0.006
Kuchenbuch and Buczko, 2011
J. Plant. Nutr. Soil. Sci.
Fig. 1 Development of plant-available P(CAL) values (LS-means) in soils over the
years within the stockless and dairy farming system and on grassland and acceptable
lower threshold

11. RECYCLED P
FERTILERS (RPFs)
RECYCLING
EFFICIENT
MANAGEMENT
REUSE

12. SOURCES OF P RECYCLING AND RECOVERY
Potential Societal P Sources
Wastewater-Based
Residues
Slaughterhouse Wastes
Organic Household
Wastes
Other Potential P
Sources
Sewage sludge based waste
residues
Main source of P to be recycled
to agriculture
Green wastes from
gardens or park areas
Food waste from retail
outlets
Almost 25%–45% of the live
weight of slaughtered animals
Processed to meat and bone
meal (MBM)
Ashes, chars, and slags from
incineration or other thermal
treatment processes
of a broad range of waste
streams

13. APPROACHES FOR P EXTRACTION FROM ORGANIC WASTES
APPROACHES
P precipitation via
chemical treatment
Thermal treatment
(P rich ash)
Struvite (by
struvite
crystallization)
Calcium
phosphates
(Prone to PTEs
contamination)
P-containing biochar
(Prone to PTEs
contamination)
Pyrolysis
Hydrothermal
carbonization
(HTC)
Alternative
methods
Traditional
combustion
Thermochemical
treatment via
calcination
In Rhenia ASH DEC
Alkali (Na/ K) replaces
carbonates
Removes PTEs
Biological
approaches
Composting
Biological
precipitation of
biosolids

14. Fig. 3. Share of
phosphorus (P)
quantities in solid and
liquid waste flows lost
from the consumption
sector (totalling 655 Gg
P) for the EU-27 in
2005; grouped from left
to right by wastewater
(blue), food waste
(green), non-food
organic waste (orange),
pet related waste (red)
and deceased humans
(purple).
Dijk et. al., 2015
Sci. Total. Environ.Fig. 2. Share of phosphorus (P) quantities in solid and liquid waste flows lost from the
consumption sector (totalling 655 Gg P) for the EU-27 in 2005

15. Fig.3. Influence of the soil pH on the relative phosphorus (P) fertilizer effectiveness (% of
water-soluble P fertilizers) of (A) phosphate rock (no. of data pairs: 173), (B) Mg-treated
biosolid ashes (no. of data pairs: 47), (C) non-H2O soluble Ca-phosphates (no. of data pairs:
19), and (D) struvite (no. of data pairs: 80)
Cabeza et al., 2011
Nutr. Cycl. Agroecosyst.
Rock phosphate
Struvite
Calcium phosphate
Mg treated biosolid ashes

16. Fig. 4. Total P and citric acid-extractable PO4-P (A, D), water-extractable PO4-P as proportion of total P (B, E)
and proportion of total P eluted as PO4-P from DGT-gel (C, F) of the thermally treated samples,
Christel et al., 2014
Bioresour. Technol.
Depending on
processing
temperature: A-C:
pyrolized pig slurry
solids (char) and D-F:
combusted pig slurry
solids (ash). Bars
represent standard
error of the mean of
three replicates;
different letters
indicate
significant differences
(p<0.05) between the
treatments (B, C, E,
F).

17. PNAC-solubility of
products from SSA
calcined at 1000°C with
Na2SO4,Na2CO3, NaOH,
K2SO4, K2CO3 and KOH
as a function of Na/P or
K/P ratio (mol/mol). The
Na/P or K/P ratio
corresponds to the molar
ratio in the starting
material.
Herzel, et al., 2015
Sci Total Environ
Fig.5. PNAC-solubility of products from SSA calcined at 1000°C with various alkali as a
function of Na/P or K/P ratio (mol/mol).

18. Fig.6. Boxplot of the relative phosphorus (P) effectiveness of recycled P
fertilizers (% of water-soluble P fertilizer). Plot indicates 50% of the
values, whiskers 90%, the thick bar indicates the mean
Moller et. al., 2017
Advances in Agronomy,
Elsevier

19. Table 2 Phosphorus concentration, P solubility and element composition in the fertilizers
and recycled P products
*With the exception of TSP, P solubility is the P concentration in water in
equilibrium with the solid fertilizer
Cabeza et. al., 2011
Nutr. Cycl. Agroecosyst.
Material Total P (%) Proportion of total P soluble in P solubility
(µmol L-1)*Water (%) 2% Citric acid
Reference fertilisers
Triple super phosphate (TSP) 20.1 90 - 115,849
Rock phosphate (RP) 11.8 0.01 17.0 6
Obtained by chemical process
Ca-P 11.1 4.1 48.6 2,901
MAP-Sb 11.0 1.1 51.0 761
MAP-Gf 9.6 0.8 47.0 508
MAP-St 11.8 1.9 43.6 1,427
Obtained by thermal process
Sinter-P 11.3 0.3 34.5 201
Sl-ash 7.8 6.4 31.4 3,210
MB meal ash 16.4 0.1 23.8 53

20. Table 3 Phosphorus concentration in soil solution three weeks after application of 60 mg P
kg-1 soil in the form of triple superphosphate (TSP), phosphate rock (PR) or recycled P
products to two soils
Different letters denote significant differences between treatments (Tukey, P< 0.05)
Cabeza et. al., 2011
Nutr. Cycl. Agroecosyst.
P sources P in soil solution
Acid sandy soil
(µmol L-1)
Neutral loamy soil
(µmol L-1)
Controls
P-0 2.1 ab 0.6a
TSP 7.2f 14.8d
PR 2.0ab 0.7a
Products obtained by chemical process
Ca-P 4.6de 1.5ab
MAP-Sb 6.0ef 9.0b
MAP-Gf 3.7bcd 4.0c
MAP-St 6.6f 8.9c
Products obtained by thermal process
Sinter-P 3.9cd 2.3ab
Sl-ash 2.2ab 1.7ab
MB meal ash 2.4abc 1.8ab

21. CONSRAINTS IN RECYCLED P FERTILISERS
APPLICATION
POTENTIALLY
TOXIC ELEMENTS
PERSISTENT
ORGANIC
POLLUTANTS
PTE Accumulation limit
Green waste- 26%
Organic waste compost- 18 %

22. RISK ASSESSMENT
Relative PTE increase
POTENTIALLY TOXIC
ELEMENTS (PTEs)
(Heavy metals
accumulation)
PERSISTENT ORGANIC
POLLUTANTS
(POPs)
PCB- polychlorinated biphenyls
PAH- Polycyclic aromatic hydrocarbons
PCDD/F-Polychlorinated dibenzo-dioxins
and -furans
Increase in PTE concentration in soil due to long term
application of RPFs
CONTAMINANTS
Indices to assess the loads of
contaminants
Heavy metal
Phosphorus
index
(HMP)
Heavy
metal
Nutrient
index
(HMN)

23. Weissengruber et al., 2018
Nutr. Cycl. Agroecosyst.
Table 4 Organic pollutant and phosphorus concentration in fertilizer dry weight for two contamination
levels
PCB- polychlorinated biphenyls
PAH- Polycyclic aromatic hydrocarbons
PCDD/F- polychlorinated dibenzo-dioxins and -furans
n.a.- not available
OF allowed in organic farming according to EU regulation EC 889/2008
Contamination level PCB (mg kg-1) PAH (mg kg-1) PCDD/F
(ng TEQ kg-1)
Low High Low High Low High
Green waste compost OF 0.01 0.04 0.38 6.40 0.003 0.005
Organic household waste compost
OF
0.01 0.09 0.38 22.0 0.004 0.005
Biosolid 0.02 0.18 18.0 46.0 0.018 0.180
Organic household waste digestate
OF
0.02 0.03 0.12 1.60 0.003 0.015
Meat and bone meal n.a. n.a. n.a. n.a. 0.0001 0.001
Solid farmyard manure 0.01 0.04 0.01 0.14 0.004 0.020

24. RPF Cd Cr Cu Ni Pb Zn Cd/P HMP HMN
Green waste compost 16.6 17.2 21.8 18.9 22.2 60.4 184 7.26 0.72
Organic household
waste compost
10.4 11.8 18.4 10.9 13.9 44.7 121 5.26 0.89
Meat and bone meal 0.6 1.2 1.7 -2.4 0.9 11.0 4.1 0.24 0.06
Biosolids 2.6 2.4 13.3 0.2 2.3 28.6 26.9 1.64 0.66
Struvite SSL 0.4 0.9 1.6 -2.5 0.9 10.6 1.17 0.05 0.03
Untreated SSA 3.8 2.9 17.5 -0.8 3.4 34.9 40.5 1.71 1.65
Rhenania ASH DEC® 0.6 3.4 8.9 -0.1 1.9 25.6 3.9 1.38 1.19
LeachPhos© 2.0 1.2 9.9 -2.3 1.1 17.2 19.8 0.90 0.88
Phosphate rock 14.2 2.7 1.6 -1.9 0.9 10.7 173 2.46 2.46
Triple superphosphate 28.3 2.6 1.6 -2.3 0.9 10.8 110 1.56 1.56
Weissengruber et al., 2018
Nutr. Cycl. Agroecosyst.
Table 5 Assessment of the Predicted Change in Soil Concentrations of Potentially Toxic Elements (%) at
Soil pH 7.0 Where Annual Precipitation Is in Excess of 100 mm, Relative to Soil Background and Soil
Threshold Values When Different Recycled Phosphorus Fertilizers (RPFs) Are Applied
SSL- Stuttgart sewage sludge leaching; SSA-sewage sludge ash
heavy metal-phosphorus index (HMP) and heavy metal-
nutrient index (HMN).

25. Fig. 7. Correlation between the heavy metal-phosphorus index and the mean
relative increase in soil concentration of potentially toxic elements (PTE) at soil pH
of 7.0 and yearly leaching of 100 kg of water m2 by 200 year application of recycled
and control P fertilizers
Weissengruber et. al., 2018
Nutr. Cycl. Agroecosyst.

26. IMPROVED P RECYLING FOR SUSTAINABLE
ORGANIC FARMING

27. APPROACHES FOR IMPROVED P RECYCLING
Primary energy
demand (FED)
Relative
Phosphorus
efficiency
LCA
performance
P recovery
rates
Global warming
potential (GWP)
Acidification
potential (AP)
Eutrophication
potential (EP)
Abiotic resource
depletion potential
(ADP)
Life Cycle
Assessment
(LCA)
Multi Criteria
Assessment
(MCA)
Hortenhuber et. al., 2017
Renewable Agric. Food Syst..
Loads of
contaminants

28. Table 6 Net Life Cycle Assessment (LCA) Results for Different Approaches of P Recovery
per kg Phosphorus (P)
ADP-abiotic depletion potential; GWP- global warming potential; FED-fossil energy demand;
AP- acidification potential; EP- eutrophication potential.
Moller et. al., 2017
Advances in Agronomy, Elsevier
ADP (kg Sb- eq kg P) FED (MJ kg P) GWP (CO2-eq kg P) AP (kg SO2-eq kg P) EP (kg PO4-eq kg P)
Organic household
waste compost
-0.78 -8.10 76.5 96.5 13.8
Biomass ash untreated -5.09 -7.48 -5.10 -10.5 -0.40
Biomass ash
chemically solubilized
50.1 27.1 32.8 69.9 3.65
Meat and bone meal -1.99 -4.54 -8.57 -1.61 -0.50
Biosolids -4.96 -6.63 -11.1 -3.20 -1.20
Ash -2.06 -3.48 1.53 0.10 -0.30
Rhenia ASH DEC 3.46 -0.14 3.80 1.80 1.15
Ash LeachPhos 6.52 0.26 7.85 11.2 1.41
Struvite 54.6 29.4 15.7 24.6 4.20
Rock phosphate 596 0.67 0.50 0.30 0.20
Triple super
phosphate
607 3.96 3.23 7.20 10.1

29. Table 7 Comparative Evaluation of the Assessed Options for Improved Phosphorus (P) Recycling Based on a Multicriteria
Assessment
Recycled P
fertilisers
P recovery
rates
P fertiliser
value
Recycling of
stable organic
matter
Greenhouse
gas emission
Abiotic
resource
depletion
potential
Eutrophication
and acidification
potential
Risk of
accumulation
of potentially
toxic elements
Risk of
negative
impacts by
organic
contaminants
Biomass ashes: Low overall P recycling potential
Biomass
ashes
++ ___ ___ ___ ___ ++ - ++
Solubilised
biomass
ashes
++ + ___ ++ ++ ___ ++ ++
Urban organic wastes: Intermediate overall P recycling potential
Green waste
compost
++ ++ ++ --to+ - ___ - -
Household
waste
compost
++ ++ ++ --to+ - ___ - -
Slaughterhouse wastes: Intermediate overall P recycling potential
Meat and
bone meal
(MBM)
++ - ___ ++ + ++ ++ ++
MBM
digested
++ - ___ ++ + ++ ++ ++
MBM ash ++ ___ ___ ++ + ++ ++ ++

30. Table 7 Continued
For: -- very low performance or very high negative environmental impact; - low performance or high to neutral
negative environmental impact; +, high performance or neutral to low positive environmental impact; ++, very
Moller et. al., 2017
Advances in Agronomy, Elsevier
Recycled P
fertilisers
P recovery
rates
P fertiliser
value
Recycling of
stable organic
matter
Greenhouse
gas emission
Abiotic
resource
depletion
potential
Eutrophication
and acidification
potential
Risk of
accumulation
of potentially
toxic elements
Risk of
negative
impacts by
organic
contaminants
Sewage sludge-based recycled P fertilizers: high overall P recycling potential
Dewatered
biosolids (SS)
++ ++ ++ ++ ++ ++ - --
Untreated
sewage sludge
ashes(SSA)
++ -- -- + + ++ - ++
Solubilised SSA
(LeachPhos)
+ + -- - - -- ++ ++
Rhenia ASH
DEC
++ + -- + - + + ++
Mephrec slags + + -- -- -- + + ++
Struvite -- ++ -- -- -- --to+ ++ ++
Ca- Phosphates -- - -- -- -- ++ ++ ++

31. Circular Economy of Phosphorus Recovery and Recycling
European Commission’s circular economy package provides a concrete example for creating a
level playing field for both primary- and secondary-based materials destined for fertilizer use.
Even then the so-called technical nutrient recovery is missing a demand-side driven market pull
for recovered (secondary) nutrients.
Therefore, the biggest challenge will be bridging the gap between supply (recovery) and demand
(recycling), especially when it comes to new types of materials or products, not already established
on the market (Kabbe, 2019).
P
ECONOMY
DEMAND
(RECYCLING)
SUPPLY
(RECOVERY)

32. Inferences drawn
P fertilizing strategies for organic farming should clearly address site-specific soil reserves. And in
the future identification of suitable fertilizers from P deposits and human waste streams general
principles must be revised to overcome the legal predicament of organic farming on the right
fertilizer source.
Plant P availability of many recycled P fertilisers (RPFs) is higher than that of phosphate rock.
Thus, if organic farmers need external P inputs there are alternatives to phosphate rock.
Chemical treatment of ashes for production of a plant available P fertilizer is related to a strong
increase in the use of abiotic resources and higher GHG emissions
❑ Thermal treatments hampers the P fertilizer value of Recycled P fertilisers, higher the
incineration temperature during thermal treatments, the stronger is the decrease of the P
fertilizer value.
❑ High scores calculated for the direct application of biosolids shows the relevant advantages of
their use in agriculture.

33. Most approaches to P recycling have benefits and risks, resulting in contradictory rankings of
recycling approaches and sources for each impact category
Life Cycle assessments show that rather simple approaches to treat recoverable P sources
provides a more favorable environmental impact in all five impact categories than more
sophisticated ones
The challenge for the organic agriculture sector is to assess RPFs using a balanced approach that
compromises neither the principle of ecology nor the principle of care.
Inferences drawn

34. RESEARCH NEEDS
There is a lack of long-term Assessments of organic contaminants on key soil parameters
including soil biodiversity, key soil functions, and possible transfer of pollutants to the
harvested products and associated impacts on human health.
Necessity of new methods to assess the risk from PTEs in order to obtain an index or value
which represents the real risk by integrating relative toxicity of elements, likely application
rates based on nutrient contents, and local environmental conditions impacting on elemental
retention and reactivity in the soil.
One major challenge is the promotion of the use of RPFs in organic farming without
compromising the image of organic farming or consumer trust.

35. Observation is a
passive science,
experimentation is
an active science.
- Claude Bernard

36. REFERENCES
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Gosling P, Shepherd M (2005) Long-term changes in soil fertility in organic arable farming systems
in England, with particular referenceto phosphorus and potassium. Agric Ecosyst Environ 105:425–
432.
Berry PM, Stockdale EA, Sylvester-Bradley R, Philipps L, Smith KA, Lord EI, Watson CA, Fortune
S (2003) N, P and K budgets for crop rotations on nine organic farms in the UK. Soil Use Manag
19:112–118
Watson CA, Bengtsson H, Ebbesvik M, Loes AK, Myrbeck A, Salomon E, Schroder J,Stockdale EA
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AN (eds) Phosphorus: agriculture and the environment. ASA, CSSA and SSSA, Madison, pp 761–
779
C. Kabbe (2019) Circular Economy: Bridging the Gap Between Phosphorus Recovery and
Recycling. In: H. Ohtake, S. Tsuneda (eds.), Phosphorus Recovery and Recycling, © Springer Nature
Singapore Pte Ltd. 2019, https://doi.org/10.1007/978-981-10-8031-9_3