Will the Soil Save Us?

The model projected changes (above) in
global soil carbon as a result of root-soil interactions,
with blue indicating a greater loss of soil carbon to the atmosphere.
Courtesy: Benjamin Sulman, Princeton Environmental Institute

Conventional projections of global carbon dioxide emissions suggest that enhanced plant growth may help to sequester more soil organic carbon (SOC)--particularly in our soils. Under this scenario, Canada comes out a winner in Global Climate Change (GCC), with the prairie provinces expected to grow a wider range of crops with a lengthened growing season.
But, as with every aspect of GCC, this may not be the case. The paper Microbe-driven turnover offsets mineral-mediated storage of soil carbon under elevated CO2 in Nature Climate Change suggests that this is only partly true. Morgan Kelly's piece for Reporting Climate Science says:

Researchers based at Princeton University report...that the carbon in soil — which contains twice the amount of carbon in all plants and Earth’s atmosphere combined — could become increasingly volatile as people add more carbon dioxide to the atmosphere, largely because of increased plant growth. The researchers developed the first computer model to show at a global scale the complex interaction between carbon, plants and soil, which includes numerous bacteria, fungi, minerals and carbon compounds that respond in complex ways to temperature, moisture and the carbon that plants contribute to soil.

The study in NCC suggests that SOC sequestration increases under rising atmospheric carbon--but only in stabilization of ‘new’ carbon in protected SOC pools which may equal or exceed microbial priming of ‘old’ SOC in ecosystems with readily decomposable litter and high clay content (emphasis mine). However, carbon losses induced through accelerated decomposition dominate the net SOC response in ecosystems with more resistant litters and lower clay content.
So, little from column A, little from column B. An undisturbed deciduous  forest with readily composting leaves and grasses might sequester more SOC than, say, a coniferous forest. And there's no guarantee that farmland will sequester more SOC.

Problems/Solutions/Problems

"Farming near Klingerstown, Pennsylvania".
Licensed under Public domain via Wikimedia Commons

I'm currently reading The soil will save us!: how scientists, farmers, and foodies are healing the soil to save the planet by Kristin Ohlson, and while it's an interesting read, aimed at a general audience, I'm not entirely convinced by the title.
But this is not my review of Soil, but the title is serving as a jumping-off point for some other things I've been reading and thinking about. Such as how we're facing this massive increase in population over the rest of this century.
It seems we're expected to increase world population from six to eight or nine billion before we top out. And somehow we need to feed all these people, an accomplishment made all the more difficult by peak oil, global warming, and the question of equitable distribution. The argument is made by industrial agriculture advocates that without high-tech, capital intensive farming, we'll never be able to feed everyone.
But here's the thing; modern agriculture is not a solution. Hell, pre-1900 agriculture is not a solution. Agriculture is the problem. Not the only one, true, but approximately a fifth of the problem. It's not that global warming will impact our ability to grow food in different areas, it's that growing food is contributing to global warming.
The FAO reports that:

[...]estimates of greenhouse gas data show that emissions from agriculture, forestry and fisheries have nearly doubled over the past fifty years and could increase an additional 30 percent by 2050, without greater efforts to reduce them.

[...]Agricultural emissions from crop and livestock production grew from 4.7 billion tonnes of carbon dioxide equivalents* (CO₂ eq) in 2001 to over 5.3 billion tonnes in 2011, a 14 percent increase.  The increase occurred mainly in developing countries, due to an expansion of total agricultural outputs.

Meanwhile, net GHG emissions due to land use change and deforestation registered a nearly 10 percent decrease over the 2001-2010 period, averaging some 3 billion tonnes CO₂ eq/yr over the decade. This was the result of reduced levels of deforestation and increases in the amount of atmospheric carbon being sequestered in many countries.

* Carbon dioxide equivalents, or CO2 eq, is a metric used to compare emissions from different greenhouse gases based on their global warming potential.