Short- and long-term effects of soil and
crop residue management on carbon
storage in agricultural soils
Luisella Celi
Soil Biogeochemistry
Rice Agroecosystem & Environmental Research Group,
Dept. of Agriculture, Forest and Food Sciences
University of Turin, Italy.
June 18, 2015
Carbon stock in soil is a function of balance
between input and output
Decomposition Rate = f ([S], [E], T, O2, H2O, soil structure)
Substrate
Inherent degradability
Biological activity
95% of decomposition reactions are biologically mediated
Environmental conditions
Temperature and water
Aerobic/anaerobic conditions
Soil properties
pH
Occlusion and chemical interaction into aggregates
Texture
Mineralogy of finer particles
Migration in subsoil horizons
SUBSTRATE: Crop residue characteristics
Inherent degradability based on the interest of each biochemical
class for decomposer organisms
Constituents Clover plant Maize residues Broadleaf litter
Cellulose
27
30
10-22
Proteins
10
2
2-15
Lignin
11
11
25
Lipids
6
8
14
C/N
12
60
40-14
-
+
Potential degradability of
plant residues
Higher degradability of crop residues compared to forest residues
What happens when crop residues are incorporated
in soil?
CO2
Adapted from Six et al., 2002
Uncomplexed
C
Aggregate turnover
unprotected C
CO2
sorption
physically
uncomplexed C into
macroaggregates
C associated to
microaggregates
MEAN RESIDENCE TIME
Unprotected
<
Physically
CO2
<
Chemically
chemically
stabilised C
a
PHYSICAL and CHEMICAL PROTECTION is related to
TURNOVER and STABILITY of AGGREGATES
fresh
residues
new
microaggregate
CO2
CHEMICALLY OM
macroaggregate (M)
CO2
CO2
UNPROTECTED OM
occluded OM
Old and new
microaggregates
old
microaggregate
time
C DISTRIBUTION of C in different size aggregates
6
25
Increase of C in the
smaller aggregates
5
20
4
3
15
2
10
1
0
m <20
M <20
m 250-20
M 250-20
M 2000-250
unprotectedLF
5
Said-Pullicino et al., 2014
C/N Ratio
C distribution (mg C g-1 soil)
NF_S
Microaggregates
protected in
macroaggregates are
richer in C than
separated
microggregates
C/N decreases from
uncomplexed
unprotected (LF) to
m<20 m
SOIL and CROP RESIDUE MANAGEMENT affects C
STORAGE and DECOMPOSITION PROCESSES
CO2
CO2
CO2
TILLAGE
fresh
residues
TILLAGE
new
microaggregate
CO2
CO2
microaggregate
occluded OM
Old and new
Microaggregates (m)
old
microaggregate
time
EFFECTS of TILLAGE on ORGANIC MATTER
in micro and macro-aggregates
Six et al. (2000)
Tillage causes a reduction of microaggregate OM
What are the main related effects?
Reduced aggregation lowers SOM,
Cation exchange capacity and nutrients,
microbial activities that in turn contribute to
aggregation
Reduced aggregation can result in lower
macropores and biochannels that influence
water movement and availability
Impacts on leaching and loss of nutrients and
chemicals in drainage and groundwaters
However the effect of tillage can vary depending on
- scale (vertical, spatial)
- time (short- and long term)
- tillage intensity
- soil resilience, i.e. the capacity of soil to resist to
stress and disturbance
… Carbon and soil functionality recovery?
Experimental platform 1996 -2015
NW Italy, temperate climate
Alfisol, sandy-loamy, neutral
Crop rotation: maize-wheat-soy
Effect of long-term tillage vs no-tillage - Introduction of minimum tillage
NO TILLAGE
TILLAGE
MINIMUM TILLAGE
1996
C Stocks
2006
2012
time
T ----------4.9 kg m-2--------- ---4.8 kg m-2--- ---4.7 kg m-2--NT --------5.9* kg m-2-------- ---5.2 kg m-2--- ---5.4* kg m-2--1996
2006
TOC (g kg-1)
0 2 4 6 8 10 12 14
TOC (g kg-1)
0 2 4 6 8 10 12 14 0
0
0
20
20
2009
2
2012
TOC (g kg-1)
TOC (g kg-1)
4 6 8 10 12 14 0 2 4 6 8 10 12 14
*
*
*
*
Carbon recovery is slow
Different C profiles
*
Rapid changes from NT to MT in the 15-30 cm layer
40
40
60
60
80
80
100
100
depth (cm)
C profile (gC kg-1)
2009
CROP YIELD
*
T ------------------------------ 7.8 t ha-1------------------------7.9 t ha-1----NT ---------------------------- 6.0 t ha-1--------------- MT---------7.8 t ha-1 ----
UNPROTECTED Carbon and Nitrogen POOLS (g kg-1)
C (g C/kgsoil)
0-15
0
15-30
0,4
0,8
1,2
30-60
Tillage
C
No tillage
Minimum
tillage
0,00
N
0,07
0,14
0,21
No tillage favours
C accumulation in the top
layers due to a lower
degradation of unprotected
fractions
Tillage favours C
incorporation into deeper
layers where decomposition
rate is slower
Tillage
No tillage
Minimum tillage
Minimum tillage increases
unprotected C in the 15-30
cm layer
Better N cycling
STABILIZED Carbon and Nitrogen POOLS (g kg-1)
0
C
2
4
6
8
*
T
10
12
0-15
*
15-30
30-60
NT
Tillage reduced C
and N in
microaggregates
into the top layers
MT
0,00
T
N
NT
0,40
0,80
1,20
1,60
2,00
Minimum tillage
limits C and N losses
because does not
affect this fraction
MT
Organic matter in microaggregates is more than 90%
strongly stabilized through different mechanisms
Experimental vineyard
Typic
Ustorthent
Sampling area
row
PG (c)
PG (a)
PG (b)
AT (c)
AT (b)
Inter-row
AT (a)
What happens
to C dynamics when soil
does not offer strong
mechanisms
of C stabilization ?
Typic
Paleustalf
Experimental time line
TILLAGE
TILLAGE
1988
Deep tillage
vineyard planting
NO TILLAGE
TILLAGE
1994
1996
NO TILLAGE NO TILLAGE
NO TILLAGEMinTILLAGE
2010
2012
Effect of tillage vs no tillage in the Entisol
NT MT
NT T
C
Low C
No tillage
1994 1995 1996
2010 2011 2012
At the beginning very low levels of C
Good carbon recovery in 14 years
Introduction of minimum tillage causes slight reduction of C after 3
years
Effect of tillage vs no tillage on aggregate stability
AGGREGATE
STABILITY
NT T
NT MT
No tillage
1994 1995 1996
2010 2011 2012
Very low aggregate stability at the beginning
No tillage favours aggregate stability
Even minimum tillage immediately decreased aggregate
stability
C distribution in the different pools
Microaggregate C
Unprotected C  20%
Microaggregate C <60%
100
90
*
Cfraction (%TOC)
80
70
60
50
40
30
Seasonal changes of OM
in microaggregates
20
10
0
SPRING
SUMMER AUTUMN
NO TILLAGE
SPRING
SUMMER AUTUMN
MINIMUM TILLAGE
Stabilization processes mainly involve weak mechanisms
SOM-clay which can be seasonally affected
In poorly developed soils SOM can be the only cementing agent
Different mechanisms of OM STABILIZATION
in microaggregates
Clay reactivity
Hydrophobic interaction
Cation exchange
Mixed mineralogy
Me bridges between OM and clays
Ligand exchange with carboxylic groups
C stabilization
Soil resilience
17/20
CONCLUSIONS
Soil and crop residue management affects C storage in soil influencing the
equilibrium between aggregate stability and SOM conservation
Tillage reduces C storage and aggregate stability, limiting the accumulation of C
in microaggregates
In agricultural soils with <1% C, SOM recovery is very slow and requires
>10 years
The effects are emphasised in the top layer and may be negligible or opposite
downward the soil profile
Effects of no tillage on crop yield may in turn affect C accumulation: reduced
tillage may be often preferred to no tillage
Soils behave differently depending on their resistence to stress: mineralogical
characteristics of the finer particles seem to be a key factor in controlling the
stable C pool
THANK YOU FOR YOUR ATTENTION
UNIVERSITY OF TORINO
Dept. Agricultural, Forest
and Food Sciences
Soil Biogeochemistry
Daniel Said-Pullicino
Cristina Lerda
Andrea Villa
Maria Martin
Eleonora Bonifacio
Sergio Belmonte
Silvia Stanchi
Elisabetta Barberis
Environmental Agronomy
Dario Sacco
Barbara Moretti
Simone Pelissetti
Chiara Bertora
Carlo Grignani