Compost for Soils

Is it all about the carbon
Biochar can last in the soil for a long
time without breaking down (100-1000
years) and it has significant potential
for storing carbon. This stable type
of carbon does not generally provide
food and energy for soil microbes that
enhance nutrient cycling in the soil and
assist plants to increase nutrient uptake.
Compost contains both stable and
labile carbon components. The labile
fraction is accessible and easily used by
soil microbes and plants. Labile carbon
is the engine room for the soil food web.
Biochar and compost both contain
other nutrients aside from carbon,
although biochar doesn’t contain much
nitrogen. Nitrogen in biochar is largely
lost during pyrolysis while the nitrogen
in composted organic material is
conserved.
Compost is often used to replace
phosphorous, potassium and
Compost and biochar at a glance….
Compost
Adds labile and stable carbon to the soil
Adds stable (organic) nitrogen to the soil
Aids nitrogen cycling
Improves water holding capacity
Increases soil carbon while minimising heavy
metal accumulation.
Biochar - Concentrates heavy metals relative
to carbon due to carbon loss in biochar
manufacture.
Can benefit crop yield
Adds beneficial microbes to the soil and
promotes nutrient cycling
Can assist in soil remediation
Short and long term crop and environmental
benefits
Designed specifically to improve soil health
and crop productivity
micronutrient fertilisers as well as being
used as a liming agent. Microbes in the
soil feed on the compost and nitrogen is
released and made available for plants
to use over time.
Compost and biochar both contain
carbon which can improve soil health,
but the carbon in biochar can hold on
to nutrients (improved cation exchange
capacity through increased surface area
of organic matter) and stop them from
leaching through the soil. Nutrients
like nitrogen, phosphorus, potassium
are released over time from compost
for plants to use as the complex
organic structures are broken down by
microbes, or as microbes die.
Compost and biochar may be
considered as options in carbon trading
systems in the future, but there are
currently no guidelines or standards
developed for these products.
Biochar
Adds stable carbon to the soil
Nitrogen is largely lost in processing
Does not assist nitrogen cycling
Improves water holding capacity
Concentrates heavy metals relative to carbon
due to carbon loss in biochar manufacture.
No ‘glue’ from bacteria by-products
Can benefit crop yield
Provides habitat for microbes already in the soil
Can assist in soil remediation
Long term crop and environmental benefits
Better to store carbon in the soil for a long
time.
What’s right for you
Can compost and biochar improve
crop yields The short answer is yes,
but this will depend on a range of
factors including what each product is
made from and the crops and systems
under investigation.
Studies in NSW* using different
types of biochar showed increases
in yield across three crops in
rotation (maize:faba bean:maize)
when compared to a control. These
increases were similar to those seen
with a compost application. However,
applying biochar to fertile and healthy
soils would not always give a positive
response and some biochars have
adverse effects on plant growth. Not
all soils respond to biochar in the
same way.
Similarly poor soils will respond well
to compost application but compost
provides immediate benefits to most
soils and includes nutrients that are
essential for crop growth. If you are
looking to provide nutrients to your
crop as well as increase soil carbon
and improve soil structure then
compost could be the right product
for you.
Look at your specific needs, check out
the research and make an informed
choice!
For more information on compost talk
to your local MIDO (market industry
development officer) or visit
www.compostforsoils.com.au.
To read more about biochar visit
www.biochar-international.org.
www.biochar-international.org/sites/
default/files/VanZwieten.pdf
© Compost for Soils 2011
o
An initiative of Compost Australia
For more information and a list of quality suppliers, go to
www.compostforsoils.com.au
the resource for compost user