Transcript Soil Organic Matter

Energy & Agriculture and
Tillage & Soil Management
In a post-peak fossil fuel world
with a warming climate
Dr Charles “Merf” Merfield
www.merfield.com
An electronic copy of this
presentation is available from
www.merfield.com/research
Not a simple topic!
• There are no simple answers
• This presentation therefore is a bit of a
meander!
– It starts by looking at the big picture
– Then it looks at some practical things you can do
on your farm
• I hope that it will inform and entertain
• It wont give you a ‘recipe’ to take home
• I will leave plenty of time for Q&A
Putting the energy ‘crisis’ in
perspective
The earth’s energy flows
3,850,000,000,000,000,000,000,000
3.85 x 1024
Joules / yr
3.85 x 1024
Joules / yr
Energy captured by photosynthesis =
3 x 1021 J / yr which is 0.078% of solar flow
Human energy use =
2.2 x 1020 J / yr which is 0.0057% of solar flow
To scale!
Not all energy is equal
• There is no shortage of energy - the sun will
continue to shine for billions of years
• Therefore there will be no shortage of sun
derived energy, i.e., solar, wind, hydro, etc.,
• Fossil fuels are clearly finite, over a period of
decades to centuries (depending on type)
• Fossil fuels are the key driver of climate change
• We therefore must stop using fossil fuels, but
even if we don’t they will run out in human
time scales
Agriculture and energy
• Agriculture is the original source of managed
energy for human civilisation in the form of
food to power humans and livestock.
• All of the energy was originally captured by
plants (photosynthesis)
• Supplemented by small amounts of other
renewable, e.g., water and wind mills, in the
last few thousand years
Agriculture and energy
• Fossil fuels (fossil photosynthesis) utterly
changed the situation
• Agriculture was rapidly deposed as societies
main source of energy (mostly relegated to
food energy)
• It is now impossible / impractical to turn the
clock back: e.g., Europe consumes ten times
the amount of energy that is produced by its
farms in the form of food
Agriculture and energy
• Agriculture has not just be deposed as
humanities energy source: It is now as
addicted to fossil fuel as the rest of society
– To power the machines that have supplanted
muscle power
– To provide the ‘inputs’ to drive yields, especially
Haber–Bosch nitrogen
• Trying to (completely) replace fossil energy
with farm derived energy (biofuels) is a
circular impossibility!
Agriculture and energy
• Agriculture needs to change its energy use:
– To minimise its climate change impact
– To move to renewable energy
• While continuing to provide humanity with
healthy food, fibres, ecosystem and other
services that are essential for civilisation to
continue
• Not a big ask then!
The drivers of climate change
• Climate change is not simply due to the CO2
released by burning fossil fuels
• There are five main greenhouse gases:
–
–
–
–
–
water vapour (H2O)
carbon dioxide (CO2)
methane (CH4)
nitrous oxide (N2O)
and ozone (O3)
CO2 equivalents
N/A
1
25
298
N/A
Agricultures climate footprint
• Methane and nitrous oxide are produced in
large amounts by agriculture
– Methane by ruminants and from manure
– Nitrous oxide from nitrogen fertilisers and
anaerobic soils (especially rice paddies)
•
Chart next page
Agricultures direct contribution
to climate change
Rice production,
11%
Manure, 7%
Biomass burning,
12%
Soil emissions,
38%
Enteric
fermentation,
32%
Agriculture and fossil fuels
• Agricultures direct net CO2 contribution to
climate change is negative, because while it
burns fossil fuels releasing their CO2 to the air
it uses photosynthesis to pull CO2 out of the
air in much larger quantities.
• However, the captured CO2 quickly gets back
to the atmosphere when the food is eaten,
but that is not counted as agricultures
problem!
Indirect contributions
• Production of Haber–Bosch nitrogen fertilisers
uses around 1% of global energy - all from
fossil fuels
• The agricultural supply chain, e.g., machinery
production, distribution and destruction /
recycling also produces considerable amounts
of GHGs
A fine mess!
• Clearly reducing agricultures climate change
impact is not a simple matter
• Trying to find simple solutions is therefore
likely to get us into another finer mess than
the one we are currently in!
Thinking holistically
• Many of the current problems created by
science & technology are due to philosophical
reductionism
• Many of the proposed solutions and analysis
of the fossil fuel problem are also reductionist
and are therefore flawed
• Its essential to consider the issue holistically /
i.e., using a system based approach
Food miles
• Based on the energy used to move food from
farm to plate: but, it is only fossil fuel energy
that matters and it fails to include the energy
used in all the other aspects of production
• Recent example of a pineapple produced in a
greenhouse in the UK - very local, very few
food miles, cost $10,000 and the total energy
used many times that of an imported
pineapple!
A little breather!
• How about a few questions / clarifications on
matters that may be unclear?
Climate change and your farm
• Practical steps to reduce your farms climate
change impact, and potentially improve your
farming and profitability at the same time
• First some caveats
• If you think that science would have a firm
grip on such matters, you would be making a
mistake…
• The following points provide some critical
fundamental underpinnings to reducing tillage
No-till and soil organic matter
• No-till systems are widely considered to
increase the level of soil organic matter (SOM)
(of which carbon is a key component)
• This is so widespread no-till is about the only
farming practice that is considered reliable
enough in building SOM / soil carbon to be
included in carbon markets
Tillage and soil carbon
Tillage and soil carbon sequestration - What do we really know?
It is widely believed that soil disturbance by tillage was a primary cause of the
historical loss of soil organic carbon (SOC) in North America, and that substantial SOC
sequestration can be accomplished by changing from conventional plowing to less
intensive methods known as conservation tillage. This is based on experiments where
changes in carbon storage have been estimated through soil sampling of tillage trials.
However, sampling protocol may have biased the results. In essentially all cases where
conservation tillage was found to sequester C, soils were only sampled to a depth of
30 cm or less, even though crop roots often extend much deeper. In the few studies
where sampling extended deeper than 30 cm, conservation tillage has shown no
consistent accrual of SOC, instead showing a difference in the distribution of SOC, with
higher concentrations near the surface in conservation tillage and higher
concentrations in deeper layers under conventional tillage. These contrasting results
may be due to tillage-induced differences in thermal and physical conditions that
affect root growth and distribution. Long-term, continuous gas exchange
measurements have also been unable to detect C gain due to reduced tillage. Though
there are other good reasons to use conservation tillage, evidence that it promotes C
sequestration is not compelling.
Tillage and soil carbon
John Baker is one of no-till’s top komatua.
That he has said there is no reliable evidence for
no-till to increase soil carbon is a big deal
Will the real SOM destroyer
please stand up?
Soluble nitrogen and SOM
• When the use of soluble (bag) nitrogen
fertilisers first became widespread it was
claimed that they would increase SOM due to
increasing crop growth, so increasing the
amount of organic matter returning to the soil
• Good old bad reductionist thinking
Soluble nitrogen and SOM
• Most bag N fertiliser is not directly taken up
by the crop - only about 15% goes straight
into the plant
• The other 85% first cycles through the soil
biota - which is mostly microbes
• Give the microbes a load of soluble N and they
need a carbon source to ‘balance’ it out
• That carbon source is SOM
Soluble nitrogen and SOM
• The evidence from long term trials and realworld nitrogen fertiliser use efficiency is clear
• Soluble nitrogen fertilisers cause soil microbes
to consume SOM in greater amounts than the
extra crop residues can replenish
• Therefore, bag nitrogen use, reduces, not
increases, SOM
Haber–Bosch nitrogen
• If you want to do one thing in farming to
reduce your climate change impact stop using
Haber–Bosch nitrogen
– It’s production consumes ~1% of global fossil
energy
– Its application on land is responsible for most of
agricultures nitrous oxide emissions
– It is a key cause of SOM / soil carbon loss
– And it has a truck load of other downsides,
especially water pollution
“There are known knowns. There are things
we know that we know. There are known
unknowns. That is to say, there are things that
we now know we don’t know. But there are
also unknown unknowns. There are things we
do not know we don’t know.”
Donald Rumsfeld (philosopher poet?)
Tillage, climate change and energy
• With the scientific world still arguing (often
heatedly) about how agriculture and soil
management affects climate and GHG
emissions, giving firm recommendations is
something of a fools errand!
• However, these are my best bets (known
knowns) and I hope that there are not too
many unknown unknowns lurking!
Step away from the tractor
• Even though the impact of tillage on SOM is
now muddier than before, it is still something
we need to reduce, even if just because most
tillage requires power from fossil fuels (animal
draft operators can now feel very smug!)
• So why do we till (cultivate) the soil?
Tilling for all the wrong reasons
• Many people think we till to make the soil
‘better’ for crops to grow
• However, no-till / no-dig shows that as good,
even better crops can be grown without
tillage (with some caveats)
• Originally the primary purpose of tillage was
vegetation (weed and crop residue)
management
– No-tillers call glyphosate ‘chemical ploughing’
Tilling for all the wrong reasons
• Nick Poole from FAR says
The reason for much
of tillage today is so
that ‘poorly
designed’ seed drills
can pass through the
soil
Tilling for all the wrong reasons
• Many standard agricultural, and especially
horticultural seed drills and planters have
planting mechanisms that will ONLY work in
loose, friable, residue free soil
• No-till has clearly shown that such a tilth is
not required for good crop establishment
• No-till has in fact clearly shown that such a
tilth can be a hindrance to crop
establishment!
Tilling for all the wrong reasons
• The almost universal belief is that you need a
fine seedbed for good seed-to-soil contact so
that seeds can take up water to germinate
• Problem is that is utterly wrong!
• Seeds don’t take up liquid water, they take up
water as a vapour / gas
Seeds only take up water as vapour
Seeds germinating above liquid water germinate faster the closer
they are to the liquid. Seeds germinating in holes in the soil, but
without touching the soil germinate without difficulty
Stewart B. Wuest, Stephen L. Albrecht, and Katherine W. Skirvin
No-till and germination
• Most of the research in no-till was on getting
the design of the drill sorted out
• Much of that was on the correct drill slot
• Baker developed the inverted T drill slot
Baker, C. J. & Saxton, K. E.
(Eds.). (2007). No-tillage
Seeding in Conservation
Agriculture, 2nd Edition.
Wallingford, UK: Food and
Agriculture Organization of
the United Nations.
Tilling for all the wrong reasons
• Ideally we would only do enough tillage to kill
existing vegetation and then use seed drills
and transplanters that can cope with high
residue levels
• This requires a whole new suite of tillage and
planting equipment!
• This requires agronomists and machinery
manufacturers to talk to each other!
Organic min-till
• Full (continual) no-till is not an option (yet) in
organics
• Min-till is an organic option
• Min-till (generally) means non-inversion
tillage that only disturbs the top few
centimetres of soil
• Min-till is being used (by two top farmers)
• Friedrich Wenz and Richard Gantlett
Photo courtesy of Friedrich Wenz www.eco-dyn.com
Photo courtesy of Friedrich Wenz www.eco-dyn.com
Non-herbicide min-till
• While it can be done, it’s not easy, err, its
pretty dam hard
• Not an option for the faint hearted or without
a lot of experience and a dab hand with the
welder
• Lots of research and new equipment needed
to make it mainstream
Non-herbicide no-till
• Also know as crimper rolling
• Independently discovered several times
– South America – 1980s
– North America 1990s
• Oregon State University – John Luna
• Rodale Institute – Jeff Moyer
• Others ?
Cover-crop no-till cash-cropping
• Grow a weed suppressing cover-crop / green
manure
• Kill the cover-crop by rolling with a crimperroller or similar tool at full anthesis (CCP)
• Plant cash-crop directly into flattened covercrop residue / mulch
• Mulch provides weed suppression and other
benefits, e.g., nitrogen
© 2009 Rodale Institute
All photos © 2009 INIA, Uruguay
Rodale Institute in USA
• Rodale doing a lot of work on crimper rolling
in USA (Pennsylvania)
• Video…
• Listen out for the cash / cover crop
combinations used
© Rodale Institute
Crimper rolling
• When it works, it can work really well
• When it fails, failure can be total (complete
crop loss)
• Lots of ducks to get in a row:
– Right cover crop(s): sowing time, growth pattern,
time of flowering, weed suppression, N supply to
crop
– Right crops: planting time, growth habit, weed
suppression
– Etc., etc., etc., etc.,
Crimper rolling
• Trial at the BHU indicated
– Our climate is not well suited (winters too warm
and heat unit accumulation in spring too slow)
– May be useful for a few crops
• It is not full / continual no-till, it is only no-till
in the spring following the cover crop, I have
not seen any no-till transition from the cash
crop into the next cover or cash crop
Phew, nothing sounds easy!
• While min-till, crimper rolling etc., sound
great they are not easy to implement
• Compaction management is something
everyone can implement, often at little cost,
and for great benefit
• After soil nutrients, compaction has the next
largest effect on crop yields and profitability
• Compaction is a major cause of anaerobic soil,
which is a major source of GHGs from soil
Compaction
• The negatives of compaction have been
known about since before the mechanisation
of agriculture
• Farmers and growers still consistently fail to
implement compaction management systems
• Result is higher tillage costs / energy use and
lower yields
Davies, B., Eagle, D. & Finney, B. (1993). Soil management (5th ed.). Ipswich: Farming
Press Books. See also Davies, B., Finney, B. & Eagle, D. (2001). Resource Management:
Soil. Tonbridge: Farming Press Books.
Compaction management
• Two rules of thumb
– The heavier the machine the deeper the
compaction
– The higher the tyre pressure the denser the
compaction
• Compaction is not removed by removing the
tyre tracks - compaction is much deeper below the plough layer
Davies, B., Eagle, D. & Finney, B. (1993). Soil management (5th ed.). Ipswich: Farming
Press Books. See also Davies, B., Finney, B. & Eagle, D. (2001). Resource Management:
Soil. Tonbridge: Farming Press Books.
Compaction management
• Use as small / light machine with the
minimum tyre inflation pressure as possible
for the job (yeah, right!)
• Very rarely done due to the cost of multiple
tractors and amount of mucking about with
weights, tyre inflation and water ballasting
• Controlled traffic - the easier answer
Controlled traffic farming (CTF)
• Create permanent (or multi year) places in the
field for machinery wheels and human feet
(tramlines / wheelings / paths)
• The rest of the field is then free from traffic
and foot compaction and benefits hugely
• Like organics and no-till, the hard core CTF
mob are fanatical - notices on gates, traffic
police, Sunday worship, etc.,
Controlled traffic farming (CTF)
• Total adherence to the faith is not required to
get considerable benefits: keep to the wheel
marks as much as possible, and live with the
odd transgression (do a penitence)
• For vegetable farming use vegetable beds.
• For broad acre farming use the tramline
system
Controlled traffic farming (CTF)
• How do you stay on the same wheelings from
year to year, especially after pasture?
• If you’re a big flash farmer there is GPS
• If your not, use fenceline markers, e.g.,
painted post, batten, or dedicated marker
poles - this works well for veg beds as well e.g., mark every 10th bed
Reverse action tillage
• Where there is a need for the standard fine
tilth, reverse action tillage is worth while
investigating
• Normal tillage, e.g., plough, deep spring tine,
rotary hoe, power harrow, surface working,
e.g., harrows and rolls, are often working a lot
of soil just to get the top 5 cm fine and loose
enough for the seed drill
• Uses lots of energy, time and creates lots of
compaction
Reverse action tillage
• Reverse action tillage, instead of trying to
break up lots of soil to get a fine seedbed,
works by separating out the already fine soil
from the clods, plant residue and stones, and
putting the big stuff down below and leaving
the fines on the top
• The machines are generally referred to as
‘stone buriers’ e.g., RotaDarion
Reverse action tillage
• Advantage is a fine consolidated seedbed in
one pass, with considerable time saving
possible, and less compaction and total
energy used
• Disadvantage is the machines need to be
tough, so good ones are expensive, they are
power hungry so need a powerful tractor for
the size of machine) and are even slower than
a rotary hoe
Renewable powered machines
• Growing interest in electric / renewable
powered machines, e.g.,
– www.electrictractor.com
– www.brookssolar.com/news/electricTractor.html
www.brookssolar.com/news/electricTractor.html
Downsizing
• A lot of the time we use machines that are
much bigger than required - there is a lot of
opportunity for machines matched to needs
• Two wheeled tractors
– Uncommon here, but a mainstay in many parts of
Asia where many farms are under 5 ha
Two wheels good, four wheels better?
© copyright 2010 Steam weeding Ltd
www.physicalweeding.com
Conclusions
• Reducing your farms impact on climate change
is not just a case of using less fossil fuel
• Stop using synthetic N fertilisers
• Soil management is also critical
• Keeping soil in good health, i.e., high organic
matter and minimising compaction are key
• Some changes are easy - e.g., controlled traffic,
while others, e.g., min-till are hard
• Start with the easy steps first!
Energy & Agriculture and
Tillage & Soil Management
In a post-peak fossil fuel world
with a warming climate
Dr Charles “Merf” Merfield
www.merfield.com
Question time