Soil carbon sequestration and net greenhouse gas emissions

The Editor at Organic Center Newsletter reports that in Europe, there is a lively debate going on in the U.S. soil science and climate change communities about the impact of various farming systems on soil carbon sequestration and net greenhouse gas emissions.  As the underlying science is settled, models will emerge for projecting the impact of various farming systems on greenhouse gas emissions, and these models can then be used to support meaningful labeling programs and carbon trading or credit schemes.

One factor that adds complexity to such estimates is well known – the level of organic matter in the soil plays a direct role in how much additional carbon the soil can hold, and hence how the soil will respond to a given change in management practices.

In general, the higher the organic matter level in the soil, the less additional carbon the soil can sequester.  As a result, the carbon sequestration benefits of any farming system that can raise soil organic matter concentrations from, say 1.5% (i.e., a degraded soil) to 3%, are enormous and will likely take one to three decades to achieve.

But all soils have a practical limit on organic matter levels, and hence soil carbon sequestration cannot go on forever, at least not while continuing to use land for food and fiber production.

These practical realities frame an important policy issue that has not yet received any serious attention – What happens to farmers who have preserved their soil organic matter, and/or rebuilt it to near-maximum levels through, for example, several years of careful organic management?

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