Finding a solution to soil's carbon problem

Soil is a natural carbon sink but its ability to store it is being compromised. Could a return to organic farming be the answer?

If you'd told me a week ago that I would spend two days listening to people talk about soil carbon sequestration (and be gripped by it!) I would have laughed in your face.
But at the Soil Association conference (SA) this week it was the hot topic, partly because the SA is launching a report in a month or so which will conclude that organic farming practices mean that while the UK's soils are losing carbon at a rate of up to 1% a year, organic farmers sequester enough carbon to offset their emissions by 5-30%.
The background to this, as you may or may not know, is that our soils are one of the biggest carbon sinks on Earth: carbon is stored in them as vegetation falls and decomposes and becomes part of the soil. Carbon is then slowly released into the atmosphere from the soil partially as a result of microbial activity: unfortunately a study in 2005 found that England's soils were losing carbon at about 0.6% a year, which could equal an annual loss of 13m tonnes. Given that our annual emissions are about 650m tonnes, that's a worrying contribution.
Why are our soils losing carbon? One reason could be that higher temperatures increase the levels of microbial activity and respiration, another could be modern farming practices such as intensive grazing, the use of inorganic fertilisers, or breeds with shallower root systems.
Whatever the reason, Gundula Azeez, who used to be the SA's policy manager, has been looking into organic farming practices and has concluded that they could hold the answer to this problem. She found that in 34 different studies of soil carbon levels, 31 showed organic farm soils to have higher carbon levels than non-organic. Now, this isn't at all surprising, given that the use of organic fertilisers such as compost or green manure is the absolute centre of organic farming: you're basically directly putting carbon back into the soil.
But does her claim that organic farms can offset 5-30% of their carbon emissions as a result of this sequestration actually stand up to scrutiny? Here's where the arguments started, because Professor Pete Smith, Royal Society Wolfson professor of soils and global change, believes firstly that this figure is just wildly optimistic.
But secondly he contends that the problem can't be resolved by spreading organic fertilisers everywhere, because, basically, there just isn't enough. Many organic farms import some of their green manures (I spoke to one farmer who said he just begs, borrows and steals whatever he can get hold of) from other farms or parks: Smith contends that if you're putting it on one farm, you're not putting it on another.
Smith's point was contended by Peter Segger, who has been experimenting with soil carbon levels at his Blaencamel farm in Wales for 20 years now. He points out that more than 80% of Europe's organic waste is currently incinerated: if we were composting that instead of burning it, a great rip in the carbon cycle could be repaired, and a cloud of carbon dioxide emissions saved in a second.
And Thomas Hartuung put forward his own work at Barritskov, a farm in Denmark where they plan to sequester 3,000 tonnes of carbon a year for the next century. We even trooped outside to the car park to watch a demonstration of a biochar stove, the system whereby biomass is burnt in a contained space, and turns into a sort of fine charcoal rather than ash, which you then bury. You get the heat, but the carbon is not released into the atmosphere. Instead it goes into the soil; this is a really elegant piece of cycle mending.
So we had two days of arguing, ding-donging away over dinner and lunch and drinks and organic flapjacks; these guys are completely obsessed.
When I left, they were arguing still, and out of these kind of arguments, I hope, will come some proper answers. Gripping it was; absolutely gripping. Not something I ever expected to feel, I must say.