Carbon Sequestration

There is worldwide concern about the increase in atmospheric CO2 and other greenhouse gases (GHG) because of their impact on global climate change. Emissions from agricultural systems are considered to be responsible for 10 to 20 % of the annual increase in anthropogenic GHG emissions. Agricultural soils have significantly contributed to the increase in atmospheric CO2 as all soils have lost on average 23% of their C since cultivation. Terrestrial ecosystems are considered potential major future sinks of C and could partially offset the increase in atmospheric CO2. Enhanced C sequestration in soils requires either an increase in primary productivity without an equivalent increase in mineralization of plant residues and soil organic matter (SOM), or a decrease in C mineralization without commensurate decrease in primary production. As conservation tillage usually enhances the sequestration of C by soils, it has the potential to contribute to the mitigation of climate change. However, results from many experiments around the world show that conservation tillage may increase emission of N2O under some circumstances, offsetting C sequestration benefits. Thus, the overall impact of conservation tillage on climate change remains to be proven.

An ongoing field project is conducted to test that in a typical CA Central Valley farming system, a reduction in the rate of soil C cycling, induced by minimum tillage, leads to a predictable increase in soil C sequestration and a change in greenhouse gas emissions across the landscape.

This field project, funded by the Kearney Foundation of Soil Science, includes the following objectives:

1. To identify and quantify C input pathways and their spatial and temporal variations at the field scale;
2. To determine the effect of minimum versus standard tillage on the spatial distribution of the controlling factors and resulting short-term rates of C cycling and of CO2, N2O, NO, and CH4 fluxes;
3. To test and improve existing C and N models to predict long-term soil C sequestration and greenhouse gas emissions along with the uncertainties at the field scale following the implementation of minimum tillage.


Poch,R.M., J.W. Hopmans, J. Six, D.E. Rolston, J.L. MacIntyre. 2005. A field-scsale carbon budget for furrow irrigation. Submitted. Agriculture, Ecosystems and Environment.

Hopmans, J.W. 2004. Review of ‘The Potential of U.S. Forest Soils to Sequester Carbon and Mitigate the Greenhouse Effect’ (Eds. J.M. Kimble, Linda S. Heath, Richard A. Birdsey, and R.Lal). Vadose Zone J. 2004 3:734-735. DOWNLOAD: PDF