WSU News

Climate friendly farming can aid carbon sequestration

By Sylvia Kantor, WSU Center for Sustaining Agriculture and Natural Resources
 
 
PULLMAN, Wash. – Farm management practices can provide a real—though modest—contribution to carbon sequestration in the Pacific Northwest. This is the conclusion suggested by two recently published studies by Washington State University researchers in crop and soil sciences and biological systems engineering.   
 
Soils compared for carbon content
Soil from an annual wheat field, left, compared
to soil from a perennial wheatgrass field. Perennial
crops can store more soil carbon than annual crops.
(Photo courtesy of The Land Institute)
 
But the interrelated processes at work with agriculture and climate disruption (in which carbon is implicated) are complex, and the tradeoffs between different farm management practices must be evaluated.
 
“Before we promote a given system or practice as ‘good for the climate,’ we need to more fully quantify the total impact,” cautions Chad Kruger, director of the Center for Sustaining Agriculture and Natural Resources (CSANR) at WSU.
Soil stores lots of carbon
 
Globally, carbon moves between the land, atmosphere and oceans. This carbon cycle, along with similar cycles for water and nitrogen, contributes to an intricate web of interactions that are crucial to sustaining life on Earth.
 
Throughout this cycle, carbon is stored in and released from various places, including soil. Carbon stored in soil accounts for roughly three times the amount stored in the atmosphere and more than four times the amount stored in living plants and trees.
 
Basically, the more productive the soil—that is, the more plant life or biomass it can support—the more carbon it can potentially store (at least until it reaches a state of equilibrium, at which point the soil is holding all the carbon it can).
 
Soil tillage a factor
 
Soil productivity is influenced by several key factors, including precipitation, fertilization, crop rotation, the use of perennial crops, organic soil amendments and tillage (turning or disrupting the soil). Tillage reduces the amount of stored carbon by exposing crop residue to air. Once exposed, the carbon combines with oxygen to release carbon dioxide (CO2) into the atmosphere.
 
CO2 is a greenhouse gas that contributes to the warming of the Earth by trapping the sun’s heat. A relatively small change in the amount of carbon stored in soil (for instance, due to tillage) could significantly influence greenhouse gas concentrations in the atmosphere.
 
That’s why evaluating the impact of alternative practices like reduced-till and no-till farming is of great interest to scientists, growers and policy developers.
 
Many factors to consider
 
It is difficult to produce an exact number for the amount of carbon that can be stored in Pacific Northwest soils, but the “modest” contribution is in the range of less than one percent of Washington’s total greenhouse gas emissions, according to Georgine Yorgey or the CSANR. Nonetheless, the promise of soil carbon sequestration is considered real enough (and the climate change situation serious enough) to warrant further investigation.
 
Some farming facts to compare and evaluate would include:
* Using nitrogen fertilizer can increase nitrous oxide (a potent greenhouse gas) emissions and thus counteract the benefit of soil carbon sequestration.
* Including legumes in a cropping system requires less nitrogen fertilizer but produces less biomass and therefore stores less carbon than cereal-based crops.
* Organic farming systems tend to be more dependent on tillage to control weeds, and tilling soil requires fossil fuels and releases stored carbon.
 
Further study and science-based information will be critical for developing policy, carbon markets and sound farm management practices. Studying soil carbon storage offers plenty of opportunity to contribute to the evolving science behind the relationship between agriculture and climate change.
 
The studies: 
“Soil carbon sequestration in the dryland cropping region of the Pacific Northwest,” by Brown and Huggins 2012; available online at http://bit.ly/YtFHs4
“Carbon storage and nitrous oxide emissions of cropping systems in eastern Washington: A simulation study,” by Stöckle et al 2012; available online at http://bit.ly/UzmpUr