A presentation from the WCCA 2011 conference in Brisbane.

1. Soil organic carbon accumulation in
Conservation Agriculture:
a review of literature
Sandra Corsi a, b
Michele Pisante a
Amir Kassam b
Theodor Friedrich b
a University of Teramo, Agronomy ad crop sciences research and education center
b Food and Agriculture Organization of the UN

2. The challenges for agriculture
HIGHER FOOD CONSUMPTION
WATER
Resources outlook
FUTURE CLIMATE
irregular water availability,
extreme weather events,
GENERATIONS LAND CHANGE
higher normal temperatures
GENETIC RESOURCES
GROWING WORLD POPULATION

3. Traditional agricultural systems Vicious circle

4. Sustainable agricultural systems Virtuous circle

5. CA is based on three principles applied simultaneously (FAO, 2009):
Conservation agriculture systems
1 2 3
Minimum mechanical Permanent organic Diversified crop rotations including
soil disturbance soil cover cover crops
(the minimum soil (retention of adequate (to help moderate possible
disturbance necessary to levels of crop residues on weed, disease and pest problems)
sow the seed) the soil surface)

6. Factors influencing C sequestration
• agronomic management
• rotation pattern
C sequestration
• input rates of organic matter
• chemical composition of organic matter inputs
• soil type and texture
• previous land use
• climatic conditions

7. LITERATURE SURVEY
No C accumulation in the soil associated with:
• soil disturbance
•
C sequestration
poor management of crop residues
• monoculture
• rotations that do not guarantee a positive N balance
• soil sampling in deep soil layers

8. LITERATURE SURVEY
Where CA principles and methods are not followed
• soil disturbance
SOC accumulation is a reversible process: with even a single tillage event, sequestered
soil carbon and years of soil restoration may be lost (Grandy et al., 2006)
C sequestration
Formation of stable micro-aggregates within macro-aggregates is inhibited under TA
(Six et al., 1998)
In TA soils the mixing of the litter favours bacteria, hence quick degradation processes
(Beare et al., 1992; Guggenberger et al., 1999)
The mouldboard plough disturbs the highest soil volume, produces the maximum CO2
flux and uses the most energy. NT the least (Reicosky et al., 2005)
Tillage erosion is the major cause of the severe soil carbon loss on upper slope positions
of pland landscapes (Lobb et al., 1995; Lobb and Lindstrom, 1999; Reicosky et al., 2005)

9. LITERATURE SURVEY
Where CA principles and methods are not followed
• removal of crop residues
• mixing of crop residues
C sequestration
Residues mixed into the soil decay more rapidly (Magdoff and Weil, 2004)
Mixing readily decomposable carbon into native soils induces a priming effect;
the composition of crop residues not mixed does not affect the decay of the native SOM
(Chadwick et al., 1998; Flessa and Beese, 2000; Kuzyakov et al., 2000; Chantigny et al., 2001; Bol et al.,
2003; Fontaine et al., 2004; Sisti et al., 2004; Fontaine, 2007)
In a soil not tilled for many years SOM active fractions increases
(Franzluebbers et al., 1995; Stockfisch et al., 1999; Tebrügge and During, 1999; Horáček et al., 2001)
Soil enzymes activities higher in cropping systems with cover crops or
organic residues
(Dick, 1994; Karlen et al. 1994; Bandick and Dick 1999; Kandeler et al., 1999; Dilly et al., 2003; Balota et al.
2004; Nurbekov, 2008)

10. LITERATURE SURVEY
Where CA principles and methods are not followed
• monocropping in NT systems
Monoculture is in itself a reason for exclusion from CA systems
C sequestration
Changing monocrop to multicrop rotation results in positive influence on SOC
concentration
(Havlin et al., 1990; Entry et al., 1996; Mitchell et al., 1996; Robinson et al., 1996; Robinson et al.,
1996; Buyanovsky and Wagner, 1998; Gregorich et al., 2001; Lopez-Fando and Pardo, 2001)
• fallow-based crop ‘rotations’
These should not be associated with the concept of CA

11. LITERATURE SURVEY
Rotations that do not allow C sequestration
• barley - wheat - soybean
(Angers et al., 1997)
Barley is a versatile species often cultivated where growing conditions are less favourable
C sequestration
• maize - wheat - soybean
(Yang and Kay, 2001; VandenBygaart et al., 2002)
These experiments are based on too few soil profiles sampled and the previous land use
is not mentioned
• soybean as the only legume in the rotation
(Machado and Silva, 2001; Freixo et al., 2002)
When a green-manure crop with high annual aboveground biomass production is
included, carbon stocks are significantly greater under CA than under TA
(Diekow et al., 2005)
C accumulates in the soil when the N balance of the rotation is positive
(Sidiras and Pavan, 1985; Bayer and Mielniczuck, 1997; Boddey, 1997; Alves et al., 2002, 2003, 2006; Sisti
et al., 2004; Bayer and Bertol, 1999; de Maria et al., 1999; Amado et al., 1999, 2001; Bayer et al., 2000 a,b).

12. LITERATURE SURVEY
Mechanisms for deep C sequestration
In the medium term, C concentration in deep soil layers is higher under
TA when the C-enriched top layer is turned upside-down
(Baker et al., 2007)
 recalcitrant C from deeper layers becomes exposed to rapid mineralization at the surface
C sequestration
 SOC accumulated ceases and regresses as soon as the external carbon input is interrupted
In the long run, in CA system the depth of the O horizon increases
 translocation of soluble carbon compounds from surface residues
(Eusterhues et al., 2005; Wright et al., 2007)
 roots, due to their chemical recalcitrance, contribute twice the C than surface residues
(Hussain et al., 1999; Wilts et al., 2004; Johnson et al. 2006).

13. LITERATURE SURVEY
Correctly assessing C sequestration potentials
• rates should be referred to specific C pools, as each C category has
C sequestration
different turnover rates
• undisturbed soils under natural vegetation should be used as
benchmark and compared to soils disturbed by human activities
• data analysis should be carried out, at the most, at the level of
agro-ecological zones

14. Is the carbon budget for CA higher than for TA?
• mechanical equipment
 farm power requirements
 number of passes across the field
 tractor life
C sequestration
 fuel consumption
 depreciation rates of equipment
• fertilization
quantity of nitrate leached  soil protection
function of mineralization of
organic N in post-harvest  N immobilisation
• GHGs emissions
 methane emissions from rice fields
 nitrous oxide emissions

15. Benefits of CA over TA
• higher biological activity
• improved capture and use of rainfall
• less peak runoff
Conclusions
• energy savings
• lower production costs
• incorporation of new areas into production
• reduced CO2 emissions
But:
introduction of CA takes time before all advantages become
apparent

16. Constraints to CA implementation
• Cultural background (tradition, prejudice)
• Lack of knowledge on how to implement CA (know-how)
Conclusions
• Inadequate policies
• Lack of experience of the tractor driver
• Lack of adequate seeding equipment
• Poor weed control
• Poor management of residues

17. Thank you for your attention