Conclusions

Carbon sequestration in soils, which is linked to the adoption of NT practice, is being promoted as a viable strategy for reducing GWP. The analyses presented here show that:

1. Carbon sequestration potential will largely be associated with heavier textured soils that have been carbon degraded due to intensive tillage.

2. The carbon sequestration benefit expected with a switch from CT to NT for rainfed corn production in the United States may be largely offset by increased emissions of N2O from soils associated with the tillage change and from increased use of fertilizer N.

3. The cumulative GWP outcome associated with a switch from CT to NT will depend on whether changes in other GWP components permanently supplement or offest carbon sequestration, and the timeframe of analysis. The long-term outcome of conversion to NT could possibly be to increase GWP, even though there may be short-term GWP benefits.

These results highlight the need for more comprehensive analysis of the GWP effects of carbon sequestration in soils. There is no scientific basis for promoting carbon sequestration in the policy arena at the present time because its true potential to mitigate GWP has not been determined. Policymakers have the right to expect objective, rigorous scientific advice, and they, in turn, need to be better informed and more questioning about the various components that contribute to GWP.

It is also well established that fossil fuel combustion is, and will continue to be, the most important source of GWP. Anthropogenic emissions of N2O and CH4 are estimated to contribute 6% and 20%, respectively, to global radiative forcing (IPCC, 2001), and agriculture is the major contributor of these gases. Given these facts, in my view, agriculture can best contribute to reducing GWP by focusing on the production of plant biomass for use as an alternative to fossil fuel and on the reduction of agricultural sources of N2O and CH4.

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