This document discusses soil organic carbon (SOC) and ways to increase it in soils. It describes how increasing SOC can improve soil health, plant productivity, and resilience to climate change. Methods discussed to increase SOC include increasing plant inputs through practices like reduced tillage, cover crops, and switching from annual to perennial crops. Maintaining or increasing SOC provides benefits like improved soil structure and nutrient cycling through increased microbial activity. Biogeochemical techniques described can help reveal pathways of carbon transformation and transport in soils. Understanding how climatic factors affect soil processes will be important for achieving sustainable agriculture as the population grows.

1. Rothamsted Research
where knowledge grows
Rothamsted Research
where knowledge grows
Dr Jennifer Dungait
CIAT-Colombia
30 09 15
Soil Organic Carbon – devising a
single proxy measure for the
sustainability of pastoral systems

2. Broom’s Barn (1987)
North Wyke (2009)
Harpenden (1843)
Rothamsted Research in 2015

3. North Wyke Farm Platform

4. Global Farm Platform Partners and Farms
http://www.globalfarmplatform.org/

5. Soil Organic Carbon – devising a single proxy
measure for the sustainability of pastoral
systems
Global Farm Platform Priority: Soil Health
Global data set to reveal the relationships between SOC and soil
health and plant productivity and quality.
A global network of sites with a suite of management practices that
can improve soil health (SOC).
Sustainable ruminant livestock systems that are resilient to change

7. Rothamsted Research
where knowledge grows
Rothamsted Research
where knowledge grows
Agriculture is the ‘largest threat to
biodiversity and ecosystem function of
any single human activity’.
Millenium Ecosystem Assessment (2005)

8. Agriculture and soil degradation

9. 0
1
2
3
4
5
6
7
8
9
1850 1875 1900 1925 1950 1975 2000
Wheatgrainyield(tha-1)
Unmanured continuous wheat =
Introduction of new wheat variety
fallowing
liming
herbicides
fungicides
▲
Introduction of new farming practice
10
Continuous wheat:
FYM =
PK + 144 kg N =
▲
1st wheat in rotation:
FYM + spring N =
Best NPK fertiliser =
2025 2050
Potential yield
increase?
SOM
management
Moreeffective
nutrient capture
Broadbalk
Classical
Experiment
YIELD GAP
Dungait et al. (2012). Advances in the understanding of nutrient dynamics and management in UK agriculture. Science of
the Total Environment 434, 39-50.
Managing soils to close the yield gap?

10. Carbon – the friendly element!
Soil organic matter (SOM)
contains:
• Soil organic carbon
(SOC) (57%)
• Nitrogen
• Phosphorus
• Sulphur
• Microelements
Dungait et al. (2012) Advances in the understanding of nutrient dynamics and management in UK agriculture. Science of the
Total Environment 434, 39-50.

11. WHY increase SOC?
Acknowledgements: Rattan Lal

12. FAST
FASTFAST Variables
SLOW Variables
SOC increase needs patience!
Carpenter & Turner (2000) Hares and tortoises: Interactions of fast and slow variables in ecosystems. Ecosystems 3, 495-
497.
Rapidly-cycling
Easily accessible
Goal-oriented
Slow-cycling
Less obvious
Underlying

13. WHAT is SOC?
Mostly decomposed plant Soil microorganisms <5%

14. HOW to increase SOC
Increase inputs
- Land use change (arable to
perennial crops)
- Increase carbon in subsoils
Kell (2011) Breeding crop plants with deep roots: their role
in sustainable carbon, nutrient and water sequestration.
Annals of Botany 108, 407-418.

15. Increase perennial plants
Fibre, forage and food
AND
carbon storage
FORAGE GRASS PERENNIAL GRAINS?
Glover et al. (2010) Increased food and ecosystem security via perennial grains. Science 328, 1638-1639.

16. 2013 Festulolium cv Prior
Lolium perenne x Festuca pratensis
Designing grasses for ecosystem services
Forage production
Flood alleviation
Drought resistance
Carbon sequestration in subsoils

17. Root biomarkers
w-hydroxycarboxylic acids
a,ω-hydroxycarboxylic acids
Quantifying root inputs
Core
Mendez-Millan et al. (2010) Molecular dynamics of shoot vs. root biomarkers in an agricultural soil estimated by natural
abundance 13C labelling. Soil Biology and Biochemistry 42, 169-177.

18. How to increase SOC
Increase inputs
- Land use change (arable to
perennial crops)
- Increase carbon in subsoils
- Organic amendments (manures
and biosolids)

19. CAUTION! Pollution swapping!

20. C3
C4
0 – 23 cm
0 – 5 cm
Recalcitrant?
How does manure increase SOC?
Dungait et al. (2005) Quantification of dung carbon incorporation in a temperate grassland soil following spring application
using bulk stable carbon isotope determinations. Isotopes in Environmental and Health Studies 41, 3-11.

21. Is lignin recalcitrant in soil?
Dungait et al. (2008) Off-line pyrolysis and compound-specific stable carbon isotope analysis of lignin moieties: a new
method for determining the fate of lignin residues in soil. Rapid Communications in Mass Spectrometry 22, 1631-1639.
Large decreases in lignin
abundance after 1 year
Lignin decomposition is
monomer-specific

22. Increase recalcitrant SOC??
Dungait et al. (2012) Soil organic matter turnover is governed by accessibility not recalcitrance. Global Change Biology 18,
1781-1796.

23. Increase inputs
- Land use change (arable to
perennial crops)
- Increase carbon in subsoils
- Organic amendments (manures
and biosolids)
Reduce losses
- Reduced tillage (green
mulches and crop
residues)
HOW to increase SOC

24. Soil organic carbon: 0.93%
Soil organic carbon: 2.65%
Conventional tillage (CT)
No till (NT100)
Herbicide resistant maize (‘Liberty-link’)
SOC and drought resistant

25. Min tillage: increases SOC, reduces losses
Beniston et al. (2015) Carbon and macronutrient losses during accelerated erosion under different tillage and residue
management. European Journal of Soil Science 66, 218-225.
More new, soil carbon under no till
(NT100)
Less soil lost under no till (NT100) –
all new
More older, soil carbon lost from
conventional till (CT)
Old carbon (>40 years)
New carbon (<40 years)

26. Reduce losses
- Reduced tillage (green
mulches and crop
residues)
- Reduce leaching of DOC
- Reduce erosion
HOW to increase SOC

27. Lignin in leachates from soils
Williams et al. (2015) Contrasting temperature responses of dissolved organic carbon and phenols leached from soils. Plant
and Soil, 1-15. doi.org/10.1007/s11104-015-2678-z
Lignin monomers – biomarkers of
terrestrial vegetation
Direct correlation between total
dissolved organic carbon (DOC) loss from
soils
Weak relationship with phenol loss from
soils

28. Catchment scale research
CATCHMENT SCALE (KM)
Collins et al. (2013) Catchment source contributions to the sediment-bound organic matter degrading salmonid spawning
gravels in a lowland river, southern England. Science of the Total Environment 456, 181-195.
Bulk stable isotopes can be evidence of
SOC transport at the catchment scale

29. Biomarkers for different plant species
n-C27 represent trees and shrubs
n-C29/31 are the predominant chain lengths in
many (but not all) grasses
Sphagnum be typified by n-C23 and n-C25
alkanes
n-alkane = straight chain
Puttock et al. (2014) Woody plant encroachment into grasslands leads to accelerated erosion of previously
stable organic carbon from dryland soils. JGR: Biogeosciences 119, 2345-2357.
Norris et al. (2013) Biomarkers of novel ecosystem development in boreal forest soils. Organic Geochemistry
64, 9-18.

30. n-C29 dominant
GRASS
n-C27 dominant
WOODY
Source of sediment in salmon gravels

31. PLANTS RIVER SEDIMENTS
Tracking C erosion from maize
12‰
4‰
30% of OC in rivers from maize?
Mean d13C values of n-alkanes (n-C25:n-C31)

32. Faecal contamination of cress beds
Gill et al. (2010) Archaeol - a biomarker for foregut fermentation in modern and ancient herbivorous mammals? Organic
Geochemistry 41, 467-472.

33. WHAT DOES SOC DO?

34. More SOC = more microbes
Beniston et al. (2014) Soil organic carbon dynamics 75 years after land-use change in perennial grassland and annual wheat
agricultural systems. Biogeochemistry 120, 37-49.

35. More microbes = more aggregates
Hirsch et al. (2009). Starving the soil of plant inputs for 50 years reduces abundance but not diversity of soil bacterial
communities. Soil Biology and Biochemistry 41, 2021-2024.
Arable + grass Control

36. Soil microbes share carbon
Dungait et al. (2013) The variable response of soil microorganisms to trace concentrations of low molecular weight organic
substrates of increasing complexity. Soil Biology and Biochemistry 64, 57-64.
methods:
nalysis of soil microbes
onents of cell walls
O
OH
OH
P
O
O
O
ell death
s)
_
Phospholipid fatty acids (PLFA)

37. Earthworms share carbon
Bacteria Plants/fungi de novo
Dungait et al. (2008) Enhancing the understanding of earthworm feeding behaviour via the use of fatty acid d13C values
determined by gas chromatography-combustion-isotope ratio mass spectrometry. Rapid Communications in Mass
Spectrometry 22, 1643-1652.

38. Management changes microbial
responses to temperature change
EnhancementCompensation
Soil microbial response to temperature
change is absent or negative in low C
managed soils!
Karhu et al. (2014) Temperature sensitivity of soil respiration rates enhanced by microbial community response. Nature 513,
81-84.

39. Global decomposition transect
n-alkanes from plant waxes
Carbohydrates from plant cell walls and microbes
Lignin from plant cell walls

40. • Processes in soils are very difficult to study
because the soil is a ‘black box’, and a complex
matrix with multiple physical, biological and
chemical variables.
• Biogeochemical approaches can help to reveal
pathways of transformation and transport that
are sometimes counter-intuitive.
• The effect of climatic variables (temperature and
rainfall) on soil processes and how they will
change as the human population grows must be
considered to achieve sustainable agriculture.
Conclusions

41. Acknowledgments
THANK
YOU
SOC: We should not ‘hoard it’,
we should ‘use it’! Janzen, 2006