This blog post is by Motu Research Analyst Zack Dorner.
Earlier this year, AgDialogue participant Rick Braddock sent us through this article, written Clayton Wallwork from the Carbon Farming Group, about Biological Farming. Rick Braddock is Operations Director of Farming
New Zealand, an agricultural investment fund established to aggregate large
pastoral farms under a New Zealand ownership model, as well as a trustee of the
Carbon Farming Group.
Biological Farming is a farming practice that
is still being developed and aims to use natural rather than synthetic
fertilisers. We at Motu decided to ask some soil scientists about the potential
for Biological Farming to store soil carbon, as a way of removing carbon
dioxide from the atmosphere.
As noted in the Carbon Farming Group article, evidence
to date around Biological Farming is largely anecdotal, and each farm has
different Biological Farming techniques applied to it, based on its unique
circumstances.
Troy Baisden from GNS Science
told us about what may cause changes in soil carbon in traditional intensive
farming system, and how this might differ under a Biological Farming system.
Biological Farming systems may be less prone to losing soil carbon compared
with traditional intensive systems, but Troy emphasises there is no clear
evidence Biological Farming will gain soil carbon. Therefore more research is
needed before it can claim to be a reliable way of helping to address climate
change.
Troy explained to us that it is almost
impossible to store carbon in soil without nitrogen, typically at a ratio of
around ten carbon particles to one nitrogen particle. Therefore, understanding
the amount of nitrogen being stored in the soil is important for understanding
how much carbon is stored in the soil (see image below).
With intensive farming, by trying to push more
nitrogen through the system (by using more nitrogen fertiliser or importing
more feed to produce more product), farm nitrogen budgets show that despite
increasing nitrogen inputs, many farms lose more nitrogen than they gain. Counter
intuitively, it seems that cycling more nitrogen faster and faster through the
soil might eventually start to cause the overall level of nitrogen and carbon
in the soil to drop.
Troy says “We’ve been surprised at the
level of losses that seem to be occurring, and at the observation that large N [nitrogen]
losses seem to be taking carbon out of the soil as well.” Unfortunately it
remains difficult to understand why these losses are occurring and work out the
exact numbers without long-term experiments that run for decades. The one long
term study to date provides some evidence that almost three quarters of a tonne
of carbon per hectare per year are lost on traditional intensive dairy farms
(Schipper et al. 2010).
In terms of Biological Farming, Troy says:
...the main
argument [is] that you’re trying to work with a system that regulates itself
better. So it will simply tell you “no” when you try and push it too hard. ...
That’s the magic of it. ... One of the reasons why you can’t [push the system]
is you’re not going to add bag nitrogen fertiliser.
By relying on natural nitrogen fixation, such
as through clover in the soil, the soil is prevented from becoming saturated
with nitrogen to the point where it loses more than it is gaining, and the
total level of nitrogen in the soil starts to drop. The natural nitrogen fixers
shut down when the system is being run too hard, though of course this will
also place a limit on the total output of the farm. Though this might mean a
Biological Farming system isn’t losing soil carbon, it’s unclear whether Biological
Farms actually gain soil carbon.
There is very limited evidence that organic
farming systems (which are similar to Biological Farming systems) limit
nitrogen losses much better than a conventional farming system, but we still
don’t understand fully why that might be (and Troy is not aware of this
evidence having been published).
So, Biological Farming could be better at
managing stores of carbon if it is better at managing stores of nitrogen. But the
jury is still out.
Jacqueline
Rowarth, Professor of Agribusiness at Waikato University who holds a PhD in
soil science, is even less positive about Biological Farming. It’s a very
complicated picture, as carbon has many ways into and out of the soil within a
farm system. For example, Jacqueline points out that drought could be the major
cause of loss in soil carbon in the Schipper et al. (2010) study, given the study’s period and the effects of
drought during that time.
There are a number of ways in which carbon
will find its way onto and off of a farm. Like any plant, the grass will
naturally remove carbon from the atmosphere and use it to form its structure as
it grows, including its roots in the soil. On a dairy farm carbon is regularly
being exported in milk tankers, having been removed from the soil and grass through
grazing, and turned into part of the milk by livestock, rather than being put
directly into the atmosphere (this also applies to nitrogen). Less carbon will
be exported less regularly from a sheep and beef farm, through removal and slaughter
of animals.
Carbon is also being added through any
inputs brought into the farm, including extra feed such as palm kernel (though
of course this may have climate impacts elsewhere). Fertilisers such as urea
will only add nitrogen directly to the soil, and not carbon.
Another dimension within a farming system
is level of grazing. The growth of grass on soil can have a bearing on the
amount of carbon in the soil. More grass on the surface supports more litter in
the soil, which increases soil carbon. Also, different types of grasses will
support different levels of carbon being stored in the plants and soil.
With lower levels of production from
Biological Farming, and little evidence to support the claims around it,
Jacqueline says that proponents of Biological Farming, though well meaning, may
be heading down the wrong track. Strong scientific backing is vital to
informing decisions around farming systems and environmental impacts.
With all the mysteries surrounding soil
carbon, we are a long way off measuring and rewarding those storing carbon in their
soil (see this
Parsons and Rowarth 2009 article on measuring soil carbon under Kyoto on
pages 2, 5 and 6). So, if you wanted to start Biological Farming only to store
carbon in your soil, then perhaps you should wait for more evidence. And you
need to be careful who you decide to listen to. Though Jacqueline is sceptical,
Troy Baisden thinks that there’s a reasonable chance that Biological Farming
doesn’t lose soil carbon, even if we may not be sure whether it would gain soil
carbon.
In terms of switching from an intensive
farming system to a biological farming system then, it’s a big risk to do it
just to store more carbon in your soil. To decide to become a Biological Farmer,
you would have to be convinced by some the other arguments outlined in the
Carbon Farming’s document, attached to this post. No doubt, as evidence starts
to accumulate, the debate on Biological Farming will continue for some time.
Many
thanks to Rick Braddock, Troy Baisden, Jacqueline Rowarth and Louis Schipper
for their help in putting this post together.
Reference
Schipper, L.A.; Parfitt, R.L.; Ross, C.; Baisden, W.T; Claydon, J.J.; Fraser, S.
(2010) Gains and losses in C and N stocks of New Zealand pasture soils depend
on land use. Agriculture Ecosystems and Environment. 139: 611–617. doi:10.1016/j.agee.2010.10.005.
Further reading