Biodiversity & MDG Targets already a
huge challenge…- now add cumulative
Climate Change….
BIODIVERSITY LOSS &
ECOSYSTEM SERVICES
COLLAPSE
MDGs
(Societal Failures)
CLIMATE
CHANGE
The Perfect Storm?
what we do as a society, in the next 5 years, will likely
resonate for all life on earth over the next 10 000 years
“…fixing carbon in soils is one of
the few practical means we
currently have to actually reduce
global atmospheric CO2
levels. Building up soil organic
matter is a win–win situation for
the fight against climate change as
well as soil health and crop yields,
and must become the focus of
farmers everywhere”
Rattal Lal
Climate Change
Carbon Cycle
The oceans and soil are the biggest
carbon storage reserves
CCA and SCA/ CRA
•CSA is agriculture that sustainably
increases productivity, resilience
(adaptation), reduces/removes
GHGs (mitigation) and enhances
achievement of national food
security and development goals
(FAO 2010)
•It happens at multiple levels,
global, national, regional and
local.
Assessing CRA
Soil Health:
The continued
capacity of the soil
to function as a
vital living
ecosystem
that
sustains plants,
animals and
humans.
Soil Renaissance
Plan, USDA
95 per cent of
terrestrialdiversity
is within the soil
itself
Soils
•SOM composition; Carbon = 42%,
Oxygen = 42%, Hydrogen = 8%, Ash = 8%,
Macronutrients (N, P, K, S, Ca, Mg),
Micronutrients (Fe, Mn, B, Zn, Cu, Cl, Co,
Mo, Ni)
These different types of organisms:
•Help to control insect pests, weeds and plant diseases
•Form beneficial symbiotic relationships with plant roots
•Recycle plant nutrients from soil organic matter and minerals
back to roots and
Improve soil structure
Effects of Soil
Organic Matter
•Improves soil biology
•Increase water holding capacity
•Improves soil fertility (cation
exchangecapacity)
•improves soil structure
•provides crumb structure that
resists compaction
•decreases bulk density
•increases pore space
•increases oxygen diffusion rate
How much organic
matter is needed?
•As a guide, an additional 10 t/ha of organic matter would be
required each year for 10 years to increase SOM by 1%,
•or more realistically in current farming systems -2 t/ha each
yearfor 20 years toachievea 0.5% increase
Who is living in 1 cubic meter of topsoil?
Who’s living in the top 3 m3 of soil?
These interactions generate
several thousand chemical and
biochemical substances that have
an influence on the “system”
the liquid
carbon
pathway N & P fertilisers
inhibit the complex
biochemical
signalling between
plant roots and
microbes
C:N Ratio of SOM
determines rate of soil
building OR degradation
Determined by crops and N
fertiliser application
Estimated Carbon-to-Nitrogen Ratios
Browns = High Carbon
C:N
Ashes, wood
25:1
Cardboard, shredded
350:1
Corn stalks
75:1
Fruit waste
35:1
Leaves
60:1
Newspaper, shredded
175:1
Peanut shells
35:1
Pine needles
80:1
Sawdust
325:1
Straw
75:1
Woodchips
400:1
Greens = High Nitrogen
C:N
Alfalfa
12:1
Clover
23:1
Coffee grounds
20:1
Food waste
20:1
Garden waste
30:1
Grass clippings
20:1
Hay
25:1
Manures
15:1
Seaweed
19:1
Vegetablescraps
25:1
Weeds
30:1
C:N ratio of
compost is
around 30:1
ACTIVE ZONE OF
AGGREGATION
ACTIVEZONE OF DECOMPOSITION
0 -5 cm
CROP RESIDUES EFFECTS and
STRATIFICATION
AGGREGATES FORMATION
Sá, 2001
Building soil Organic
matter (Active and
Stable Carbon)
•Although nutrients were
more concentrated near
the soil surface for millions
of years, ecosystems didn’t
crash, and many became
increasingly robust over
millennia.
•Stratification is normal.
An undisturbed soil
covered by plant
residues encourages
the formation of
mycorrhizae, the
beneficial association
of certain fungi with
roots that enormously
enhances the
nutrient-gathering
ability of many crop
plants.
Roots, fungal hyphae, and their secretions
stabilize soil aggregates and promote good soil
structure, thus preventing compaction.
The root-hyphaenet
•Active Organic Carbonare the smaller
carbonmolecules likesugars thatcanbe
readilyconsumedbymicrobesandisregarded
as microbial food. C:N Ratio important
•Stable carbon is for instance the final
decomposed form of lignin –Humus & Humic
substances. Can not be readily further
decomposed.
Active vs stable carbon
Humus
•Like a big sponge, humus can hold up to 90 percent of its
weight in water
•Because of its negative charge, many plant nutrients stick
to humus (nitrogen, calcium, magnesium, phosphorus, and
others), preventing them from washing away and acting as
nature’s slow release fertilizer
•Humus massively improves soil’s structure, making it loose
and friable and helping plants root by providing them
better access to nutrients, water, and oxygen
•Humus may help “filter” toxic chemicals out of the soil,
much like carbon-based water filtration systems filter toxins
out of your water
Active Carbon (Particulate OM)
•It responds readily to soil management
•It is a source of food/energy for microorganisms and
soil animals as well as nutrients for plant growth.
•Particulate organic matter enhances aggregate stability,
waterinfiltration andsoilaeration;
•It increases cation exchangecapacityandbufferingpH.
•It also binds environmental pollutants such as heavy
metals and pesticides.
•Particulateorganicmattermayplayanimportantrole
in the suppression of soil borne diseases