In February/March 2011 the Royal Society held a conference on how GHG emissions from agriculture might be reduced through measures that focus on nitrogen efficiency, methane, and soil carbon sequestration. A short report has now been produced and can be downloaded here. You can also download audio recordings of the presentation.
The report draws the following conclusion:
We conclude that in the long term, even with new research outputs and effective translation, the only structural change that could be of a magnitude sufficient to even approach an 80% reduction target in the agricultural sector would be a large reduction of agricultural production in the UK, thus displacing greenhouse gas emissions to other countries. Such an action is not compatible with increasing global demand for food and would be morally irresponsible, economically unrealistic, and would have no global climate benefits as it would result in land elsewhere (undoubtedly less suited to food production) being converted to grain production to meet UK demand. Agriculture in the UK is highly efficient relative to that in most other developed countries, and climate change predictions imply that reliance upon efficient crop production in countries like the UK will increase rather than decrease over the 40 years leading up to the target date. Research has already identified improved crops, livestock and management practices which can decrease greenhouse gas emissions per kg food, but it has the potential to do much more. Combining such biological research with more effective translation of the new knowledge, underpinned by behaviour and economic research, should enable agriculture to make a significant contribution to reducing its greenhouse gas emission footprint, though an 80% reduction while increasing food production will not be feasible.