Agricultural soil carbon accumulation in North America: considerations forclimate policy

The Kyoto Protocol introduces the possibility that changes in carbon stock on agricultural and forest land and soils may be counted against countries' commitments to reduce their greenhouse gas emissions. Including activities related to land use change and forestry in the international climate chang e agreement may stimulate new incentives for soil-conservation practices do mestically. However, a primary criteria for their inclusion relates to the level of accuracy and transparency with which carbon stock changes can be a ssessed. Parties will also be concerned with the wider environmental impact of different sequestration practices, and the impact of offsets on overall emissions targets. This paper examines these issues for agricultural soils , considering recent research in North America. It is argued that incentive s for carbon sequestration practices may need to be implemented independent ly of actual stock changes because farm-level soil monitoring would be very costly. In the USA, priority should be given to establishing incentives fo r cover crops and to expanding conservation tillage programs. These activit ies provide a range of ancillary environmental benefits. In contrast, impro vements in biomass yield tend to rely on higher fertilizer inputs with thei r related environmental costs. Carbon accumulated through any of these acti vities is easily lost if the practices are discontinued, and so assessment procedures are needed that would avoid overestimating sequestration. Annual accumulation in agricultural soils could be equivalent to about 10% of Ann ex I carbon dioxide emissions, and therefore options for limiting sink cred its from soils should be considered. (C) 2000 Elsevier Science Ltd. All rig hts reserved.