CARBON IN THE UPPER SOIL LAYER
What are the implications and possibilities of soil
management for carbon storage?
Johan Bouma
Em.professor of soil science
Wageningen University
Items to be discussed:
- The carbon balance of the world
- The problem and the hypothesis
- Organic matter in soils: immense variety!
- Changes in organic matter content: land use
change, soil management and erosion.
- Outlook: the knowledge paradox.
Soil forms the top layer of the earth’s crust and
is situated between the bedrock and the surface,
excluding grondwater (EU definition)
Problem: The concentration of CO2 has increased by 35%
from 280 ppm in 1750 to 377 ppm in 2004 and is
presently increasing with 1.8 ppm/year. Adding
contributions of other greenhouse gasses ( CH4, N2O)
we assume that, as a result, temperatures may rise by
1.5-5.8C in 2100.
Hypothesis: By strongly reducing greenhouse- gas
emissions we may be able to restrict the temperature
rise to 2C by 2100, which appears bearable.
Issue in this presentation: How can soils contribute to
reducing greenhouse-gas emissions?
Koopveengrond.
Plaseerdgrond ( “cat-clay”)
Ooivaaggrond
Veldpodzolgrond
Tuineerdgrond
Zwarte Enkeerdgrond
The Dutch Soil Science Society elected the Enkeerdgrond
as being the most representative for the Netherlands. Now
(8-3-2010) in NATURALIS, Leiden.
Terra Preta: increased organic matter content in sandy
amazon soils after adding charcoal ( “biochar”) over many
years.
Major mechanisms for change of C in soil
• Land use change: estimated loss of C so far: 78Gt , rate
now 1.6Gt/year ( Lal 2010).
•Accellerated (!) soil erosion: estimated quantity so far: 26
Gt C. current rate: 1 Gt/year.
Serious downstream effects of erosion, which has a
landscape focus.
• Soil management: reduce erosion potential; increase
organic matter content of the soil.
soils can sequester 0.6-1.2 Gt/C on world level(Lal, Hillel). Ignored
potential. Example of effects of management on %C in prime agr.land
in the Netherlands (Fluvaquent).
Bulk density
org.matter
Kg m-3
•
•
•
High-tech arable land (left)
Organic farming (middle)
Permanent meadow (right)
1.68
1.47
1.38
1.7
3.3
5.0
Prepare “storylines”: for each soil type! This is the
most common sandy soil in the Netherlands.
•
•
•
A: BD = 1.30 kg/m-3
OM = 8.1% (old grassland)
B: BD = 1.36 kg/m-3
OM = 6.3%(reseeded
grassland)
C: BD = 1.48 kg/m-3
OM = 4.8% ( arable
land, often maize)
OM= 3.40-1.54 x Maize +0.19 x Old
+0.55 xGWC. (R2=0.75) (50
farms)
But..plants bind only C when they grow! So N, P, K micronutrients and
water are also important, not only for climate change but also for food
security,environmental quality and energy crops, other major issues
where soils are crucial.
Why is it that we know so much and that so little of this
knowledge is applied in the policy arena and in practice
when dealing with “wicked” problems?
J.Bouma. 2010. Implications of the knowledge paradox for
soil science. Advances in Agronomy 106:143-171.
.
Empirical
K1
Qualitative
K3
K4
K2
Quantitative
K5
pedology
Soil physics
Mechanistic
So what’s the message!
• Soils contain more C than plants and the atmosphere.
Diverse soil-potentials for C adsorption are important in
the context of climate change ( but also for other major
issues such as food security, environmental quality and
energy security). Don’t lump all soils together!
• Land use change from forest to agriculture is a major
source of CO2, followed by erosion and bad soil
management. Projected climate change will increase
risks. Improved soil management is urgently needed.
• We know what to do but we don’t get it done! The
research community has got to get its act together!
Challenge for the future: let science enable and inspire
society to jump again!!