Friday, 20 July 2012

Biological Farming and soil carbon – green wash or climate saviour?

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).

This image was pulled from this useful article in NZ Science Teacher magazine
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.


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.

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