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 centerb Food and Agriculture Organization of the UN

The challenges for agricultureRe

sour

ces

outlo

ok

FUTURE GENERATIONS LAND

WATER

GENETIC RESOURCES

CLIMATE CHANGE

GROWING WORLD POPULATION

HIGHER FOOD CONSUMPTION

irregular water availability, extreme weather events, higher normal temperatures

Vicious circleTr

aditi

onal

agr

icul

tura

l sys

tem

s

Virtuous circleSu

stai

nabl

e ag

ricul

tura

l sys

tem

s

Minimum mechanical soil disturbance

(the minimum soil disturbance necessary to

sow the seed)

1

CA is based on three principles applied simultaneously (FAO, 2009):

Permanent organic soil cover

(retention of adequate levels of crop residues on

the soil surface)

2

Diversified crop rotations including cover crops

(to help moderate possible weed, disease and pest problems)

3

Cons

erva

tion

agric

ultu

re sy

stem

s

Factors influencing C sequestration

• agronomic management

• rotation pattern

• input rates of organic matter

• chemical composition of organic matter inputs

• soil type and texture

• previous land use

• climatic conditions

C

sequ

estr

ation

• soil disturbance

• poor management of crop residues

• monoculture

• rotations that do not guarantee a positive N balance

• soil sampling in deep soil layers

C

sequ

estr

ation

LITERATURE SURVEYNo C accumulation in the soil associated with:

• 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)

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)

C

sequ

estr

ation

LITERATURE SURVEYWhere CA principles and methods are not followed

• removal of crop residues

• mixing of crop residuesResidues 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)

C

sequ

estr

ation

LITERATURE SURVEYWhere CA principles and methods are not followed

• monocropping in NT systemsMonoculture is in itself a reason for exclusion from CA systems

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

C

sequ

estr

ation

LITERATURE SURVEYWhere CA principles and methods are not followed

C

sequ

estr

ation

LITERATURE SURVEYRotations 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

• 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).

C

sequ

estr

ation

LITERATURE SURVEYMechanisms 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

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).

C

sequ

estr

ation

LITERATURE SURVEYCorrectly assessing C sequestration potentials

• rates should be referred to specific C pools, as each C category has 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

Is the carbon budget for CA higher than for TA?

• mechanical equipment

• fertilizationquantity of nitrate leached function of mineralization of organic N in post-harvest

• GHGs emissions

farm power requirements number of passes across the field tractor life fuel consumption depreciation rates of equipment

soil protection N immobilisation

methane emissions from rice fields nitrous oxide emissions

C

sequ

estr

ation

Conc

lusi

ons

• higher biological activity

• improved capture and use of rainfall

• less peak runoff

• 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

Benefits of CA over TA

• Cultural background (tradition, prejudice)

• Lack of knowledge on how to implement CA (know-how)

• Inadequate policies

• Lack of experience of the tractor driver

• Lack of adequate seeding equipment

• Poor weed control

• Poor management of residues

Constraints to CA implementationCo

nclu

sion

s

Thank you for your attention