GRF 2nd One Health Summit 2013: Presentation by Gerard Govers, KU Leuven, Belgium

1. Soils and global health
Gerard Govers, Kristof Van Oost, Roel
Merckx, Bas van Wesemael, Michael
Stocking

2. Global human health: do soils matter ?

3. Indeed: soils can make people sick
web.worldbank.org

4. Extent of As contamination

5. But soils are far more crucial to global,
planetary health
• Why ? It is only dirt, no ?

6. No: soils are crucial to global health
and provide crucial ecosystem services
– Crop production (or, more general, plant growth)
– SOC storage
– Water storage and filtration
– Nutrient cycling and retention

7. Some numbers
• Global food production: 1600 million tonnes
of grain
• Soils contain ca. 2400 Pg of carbon: that is
about three times as much as the atmosphere
• Soils store ca. 100000 km³ of water anually
that is provide to plants
• Soils cycle at least 200 Tg of N each year
• Overal economic value: trillions of dollars

8. No wonder some people attribute the
demise of entire civilisation to soil
degradation

9. And soil erosion is nowadays described
as a threat to global food production

10. Are our soils healthy ?

11. Many people have asked that question

12. At first sight: yes

13. Agricultural production per capita has risen
significantly over the last 50 years
http://www.cifs.dk/scripts/artikel.asp?lng=2&id=1712

14. Data source: FAO

15. Food price crises are real, but…

16. long-term perspective is also
important
http://www.fao.org/docrep/014/i2330e/i2330e03.pdf

17. There is considerable scope for future
gains in yields
Mueller et al., 2012

18. So, why is hunger still an issue ?

19. Hunger and malnourishment remain
important issues, but:
• They can no longer be attributed to
insufficient food production (at the global
scale)
• They are far more strongly related to access to
(good) food:
– Purchase power
– Distribution networks
– Social equity

20. What about soil organic carbon
(SOC) ?

21. It is very likely that SOC storage in soils has
increased over the last decades
Eglin et al.,, 2010

22. And many predict the SOC stock to rise
further…
Friedlingstein, 2006

23. …and the world is getting greener
www.zef.de

24. So, can we fire the soil doctor ?
http://soildoct
or.org/

25. We would argue: not yet

26. The pressure on the soil system is very
high
Many of you are familiar with the threats:
–
–
–
–
–
Soil compaction
Salinisation
Loss of soil structure
Soil erosion
Loss of soil biodiversity

27. How big are those threats ?
• For some, we have only a rough idea
• For some others, we are getting there

28. Soil erosion
• Early figures are probably overestimations
– E.g. : early estimates for Europe 17 t ha-1 yr-1,
while more recent estimates are 1-3 t ha-1 yr-1
– Global average on cropland most likely around 12
t ha-1 yr-1 rather than 30 t ha-1 yr-1
– But numbers are still impressive:
• Soil erosion redistributes ca 30 Gt of soil anually
• This leads not only to soil loss but also to loss of
nutrients: the amount of N eroded worldwide is of the
same order of magnitude than the global production of
N fertilizer

29. Detrimental nutrient losses are especially important
in low input agricultural areas
Quinton et al., 2010

30. Is this a real threat to productivity ?
Bakker et al., 2007

31. Threat varies regionally

32. What to do about it ?
• Technologies to reduce erosion do exist, are
effective, but are not always widely applied
• Sometimes because their effectiveness is not
well understood

33. Conservation agriculture

34. Conservation agriculture
Conventional
ploughing
Direct drilling
Reduced tillage

35. Effects on erosion and runoff can be tested
experimentally

36. Does not seem to work that well…
370
PRGRG, K.U.Leuven
Conventional plough (%)
360
250
200
Deep non-inversion tillage
Conservation tillage
Shallow non-inversion tillage
Direct drilling
Median
Mean
Mean
Conventional plough = 100%
Median
150
Conventional plough
Conventional plough =
100
76%
76 %
53 %
53%
50
0
58 %
58%
41 %
41 %
N = 30
n = 200
Runoff
Soil loss
Runoff Soil loss
N = 33
n = 194
100%

37. Conventional
Conservation

38. Reduction at field scale appears to be
much more important
120
99.8
90
soil loss (ton/ha)
76.3
60
30.5
30
18.0
15.7
8.6
4.1
0.0
0.0
0.0
0
2002
2003
2004
conventional ploughing
2005
conservation tillage
2006

39. Caveat
• Clearly, this is just an illustration of a single
technique that will work well under specific
conditions.
• Other technology (cover crops, mulching,
terracing) may be used under other conditions
• However, the key message is that we can
drastically reduce erosion

40. We need to assess benefits of
alternative systems realistically

41. Can management, within a given land
use, make a difference in SOC storage
in soils?
• Initial estimates: up to 1Pg C/y may be stored
by implementing adequate land management

42. No-tillage
•Temperate arable land: 0-1 Mg C/(ha yr), generally < 0.3
Mg C/(ha yr) but recent regional study found no
significant effects
•Tropical arable land: less data, 0.3-0.8 Mg C/(ha yr)

43. Agroforestry
0-1 Mg C/(ha yr), but many studies did not find significant
effects, effects sometimes overstated in literature, no
accounting for land use effects

44. Forests
Management may make a difference: potential
effect is largely unknown

45. Grasslands
Ca. 0.3 Mg C/(ha yr), but very variable

46. Organic agriculture
•Reduces, on average yields (and therefore inputs)
•Significant gains in SOC are therefore unlikely, unless
respiration rates are decreased

47. Translated to the global scale
• Gains of 1 Pg C per year due to alternative
management are unrealistic
• Realistic numbers are in the order of 0.1-0.3
Pg per year over a 50 y time span

48. Other example: effects of SOC on
yields

49. There is a nice positive relationship, no ?
Lal, 2010

50. However….
• Relationship is not always causal (i.e. SOC
increase does not always cause yield increase:
increased yield is often due to co-variation in
nutrients available to plants
Chemical fertilizers
Manure
Reference
Edmeades, 2003

51. Do not reverse causality
SOC
YIELDS

52. SOC does increase under intensive
agriculture
Minasny et al., Java

53. Better soil management is not only a
question of technology and correct
understanding
• We need to develop a vision on how to
implement this technology that may serve as a
basis for specific project.
• We need indicators to assess progress

54. GEF : developed a vision on global soil
organic carbon management

55. Soil management requires an
integrated, landscape scale approach
• Opting for low-intensity land use should account for
disturbance of ‘virgin’ SOC stocks over larger areas
(not always has to be negative !)
• Same holds for FYM-based systems: manure has to
come from somewhere
• Other landscape functions (water provision, tourism,
biodiversity) need to be accounted for

56. It is easier (and probably cheaper) to
preserve than to restore.
• Preserving a stock has immediate benefits
• Managed systems only rarely meet SOC stocks
found under undisturbed natural vegetation
(exception: specific cases of grassland
afforestation)

57. Improving crop yields and restoring
soil fertility is key to sustainable soil
management
• Higher yields means that less land is necessary
• Higher yields have a positive effect on SOC
stocks
• Higher yields make land more valuable,
thereby stimulating efforts to conserve it

58. Target soils and environments correctly

59. What was happening ?

60. Paramo afforestation dramatically
reduces water yield

61. Set goals realistically
• The response time of SOC=decades
• The sequestration rates possible under
alternative management systems may be
lower than initially proposed
• Account for negative externalities when they
are likely to occur (water yield, land use,
biodiversity…)

62. Generate co-benefits
• SOC sequestration and soil conservation in
general are often not a commercially viable
operation
• Co-benefits may be reduced labour, increased
yields, biodiversity preservation, increased soil
quality

63. Assess socio-economic conditions that
may affect potential success of SOC
management projects
• Do the farmers-land managers have access to
all relevant information ?
• Are the relevant skills present ?

64. Assess the socio-economic implications
(see also Stringer et al., 2012)
• What is the effect of pine forests on local
communities in the Paramo ?
– Where does the income generated by the wood go ?
– Are they able to deal with reduced water yields ?
– What is replacing their traditional activities in the
Paramo ?
– What will be the effect on the gender distribution of
the workload ?
– How will the arrival of the Iphone 12 in 2020 affect
these results ?

65. Besides a vision on how to improve
soil health, we also need to monitor
progress

66. How to monitor the global soil
resource ?

67. Indicators: scientists have developed
many of them
Arias et al., 2005

68. But we should look for indicators that can be
used in a farming/operational context
Doran, 2007

69. What I would propose
• Soil organic carbon levels are a good
integrator of a soil’s biological health
• Soil water availability to plants is a strong
indicator of its physical health
• Nutrient balances may help to establish sound
fertilization levels preventing excessive
nutrient leaching while guaranteeing
adequate crop yields

70. Conclusions
• The global soil system is not on the verge of a collapse
• However, there are real threats that need remediation
• Our assessment of the state of the global soil system
and the quantification of the various threats is still very
poor and we need better assessments to realistically
assess threats and develop adequate responses. A
forum such as this may help to push such a
development
• We also need to develop a set of (relatively simple)
indicators to monitor soil health:
– Soil organic carbon
– Soil water availability to plants

71. Conclusions
• We should not be pessimistic:
– The technology to improve soil health is, to a large
extent, available
– It is therefore possible to produce the food the world
population needs and, at the same time, protect the
soil resource and reduce the environmental impact of
global agriculture
– Sound application of these techniques requires not
only a correct understanding of their effects, but also
a correct understanding of the agricultural and socioeconomic effects of its implementation. Developing
such a vision is an important task for the international
community

72. Thank you !