Presentation at the 1st Summit of the Organic Fertiliser Industry in Europe (SOFIE), 5 - 6 June 2019, organized by the European Sustainable Phosphorus Platform (ESPP, www.phosphorusplatform.eu). All outcomes of the conference can be found at http://www.phosphorusplatform.eu/SOFIE2019

1. Do organic fertilisers bring benefits to
farmers beyond their nutrient value?
Can they contribute to climate change mitigation by
sequestering C in soil as in the “4p1000” initiative?
David Powlson & Andy Whitmore
Rothamsted Research, UK

2. Organic matter influences soil properties
in 3 ways:
Provides nutrients
Improves physical conditions
Energy source for organisms which mediate the first two
• Arable soils – generally low in OM and difficult to increase
substantially (depends on clay content, climate, cropping system, …)
• A little OM can have a surprisingly large effect
• OM can have an effect surprisingly quickly
• No guarantee of increased yields – but OM may increase resilience
of yields

3. Sandmarken Experiment,
Askov, Denmark
SOC increases following
arable to grassland conversion
Hu et al (2018) European Journal of Soil Science 70, 350-360
Arable
Grass
1998
• Slow decline in soil C during
105 yrs in arable
• Increased at 0.39 Mg C ha-1 yr-1
during 14 yrs under grass (18 ‰
yr-1 cf initial stock)

4. SOC changes following land use change,
Rothamsted
40
30
20
10
0
1960
90
1940
70
50
80
100
60
20001980
Year
OrganicCinsoil,tha-1
Started arable
Started grass
Johnston et al (2009) Advances in Agronomy 101, 1-57
Continued grass
Grass to arable
Arable to grass
Continued arable
Movement
towards new
equilibrium
SOC content
~50 years

5. Broadbalk – started 1843
Soil organic C in selected treatments
Unmanured
NPK
Farmyard manure (FYM) annually
FYM annually
since 1885
Points: measured data. Lines: RothC simulation

6. No manure
Manure
20 t ha-1 2yr-1
Manure
30 t ha-1 2yr-1
+NPK No inorganic fertilizer
Bad Lauchstädt Experiment, Germany (from 1902)
X-ray CT scanning
used to visualise
soil pores
Naveed et al (2014)
Geoderma 217-218, 181-189
Results:
• Manure increases pores
• Adding inorganic
fertilizers causes further
improvement
• Pores beneficial for:
– Water movement
– Root growth
Manure
NPK

7. Hoosfield,
Spring Barley since 1852
Broadbalk,
Winter wheat since 1843

8. Crop yields
• Larger organic matter (OM) content in soil where manure
applied for >100 years (x 2-3)
– much better soil structure
• Winter wheat – yield insensitive to OM content of soil
– can attain highest yield with inorganic fertilizers alone
• Spring barley – only reaches highest yield where OM content
is higher from manure applications
– but small OM increase (from fresh manure treatment) has large effect
• Likely reason for difference:
– Spring barley – short growing season, 5-6 months
– Winter wheat – 10 months – more time to overcome poor early growth

9. Manure + N
Best NPK
Best NPK
Manure + N
Control:
no manure or NPK
Winter wheat
Continuous
wheat
1st wheat
In rotation

10. Control:
no manure or NPK
NPK: low N
NPK: higher N
(best yield without manure)
Manure
Manure + N
Yield gap
(inorganic fertilizers cf. manure)
>2.5 t ha-1
Spring barley

11. Spring barley, grain yields (Hoosfield Experiment)
Whitmore et al (unpublished)
Long-continued FYM
FYM since 2001 only
Inorganic fertilisers

12. Plant & Soil 411, 293-303 (2017)
• Only included sites with
several N fertiliser rates
applied to with and without
manure treatments

13. Hijbeek et al (2017) Plant & Soil 411, 293-303
Maize at Novi Sad, 1996-2003
Max. yield without organic input
Max. yield with organic input
Difference in max. yields

14. Hijbeek et al (2017) Plant & Soil 411, 293-303
Additional yield effect of organic input
All crops, all sites
• Overall, effect on crop yields of
extra organic matter in soil –
surprisingly small
• But greater with:
– Spring-sown crops
– Crops very sensitive to soil
physical conditions, e.g. potatoes

15. 0
10
20
30
40
50
60
70
barley Potatoes Sugar beet ryegrass (pots)
OlsenPmg/kg
Moving the threshold: Olsen P required for
95% yield at two OC levels
0.87%
1.40%
Johnston, Poulton and Coleman, Advance in Agronomy 2008
Larger root system
– more effectively
exploring soil for P
SOC

16. Earthworms
Earthworm biomass significantly increased by N rate
(p<0.05) and organic addition rate (p<0.05)
0
50
100
150
200
250
N0 Compost N0 FYM N3 Compost N3 FYM
Earthwormbiomass(gm-2)
0 t C/Ha
2.5 t C/ha
3.5 t C/Ha
N0 Compost N0 FYM N3 Compost N3 FYM
Whitmore et al (unpublished)

17. https://www.4p1000.org/4-1000-initiative-few-words
Mitigation
Adaptation

18. 4 per 1000
• In principle, good
• Controversy over quantity of C sequestration
practically achievable in arable soils (as opposed to
removing soil from arable agriculture)
• Some confusion over details of soil C sequestration

19. (Burial)
107
6
2
0.1
105107
60
60
120
0.4
Global carbon: stocks and flows
Vegetation (560)
Soil (1500)
1000 million tonnes per year
(Pools) 1000 million tonnes
flows
Ocean (38000)
Atmosphere (720)

20. (Burial)
107
6
2
0.1
105107
60
60
120
0.4
Vegetation (560)
Soil (1500)
1000 million tonnes per year
(Pools) 1000 million tonnes
flows
Ocean (38000)
Atmosphere (720)
C sequestration
Either:
Greater movement from atmosphere to land
(increased plant growth)
Or
Decreased movement from land to atmosphere
(slower SOM decomposition)
Global carbon: stocks and flows

21. Confusion over organic additions
• Manure addition
– Adding manure increases soil C – good for soil quality
– And reduces N fertiliser requirement
– But generally is a movement of organic C from one land location to
another
– NOT extra C transfer from atmosphere to land
– So NOT genuine climate change mitigation
• Organic fertilisers made from “wastes”
– If they would otherwise go to landfill or be incinerated, soil C
increases ARE genuine mitigation
– But beware of over-stating magnitude of increases

22. Concluding comments 1/2
Do organic fertilisers bring benefits to farmers
beyond their nutrient value?
• Yes – improved soil physical structure and increased biological activity
• Improved root growth – increased pores
• May lead to lower required soil P concentration
• Increased water infiltration – decreases runoff and erosion risk
• Crop yields may be more resilient to annual variations in weather
(moisture retention)
• Increased soil/rhizosphere microbial population may increase
resistance to soil-borne pathogens
• BUT – increased yields not guaranteed – more likely with short
growing-season crops (spring sown) and those very sensitive to soil
physical conditions

23. Concluding comments 2/2
Can they contribute to climate change mitigation by
sequestering C in soil as in the “4p1000” initiative?
• Yes – if source material would otherwise be incinerated or
landfilled
• In contrast to animal manures (though, of course,
manures good for soil quality and nutrient supply)
• BUT – be careful, don’t claim too much: rates of soil C
increase likely to be modest, but go in right direction

24. Soil sampling on Broadbalk, 1943
Thanks for your attention !