Submitted to: Journal of Soil and Water Conservation Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 6, 2000
Publication Date: N/A
Interpretive Summary: Release of soil organic carbon to the atmosphere increases the atmospheric concentration of carbon dioxide and ultimately contributes to global climate change. There is a current need to understand how the management of croplands can be changed to reduce soil carbon losses to atmospheric carbon dioxide. Tillage systems and associated crop residue management in croplands have a big influence on net gains in stored soil carbon. Farmer adoption of conservation tillage has already reduced these carbon losses. This information will be used by farmers and environmental planners to focus on the management changes to enhance soil storage of carbon, both as to magnitude and sustainability.
Technical Abstract: Soil organic carbon (SOC) makes up about two-thirds of the C pool in the terrestrial biosphere; annual C deposition and decomposition to release carbon dioxide (CO2) into the atmosphere constitutes about 4 percent of this SOC pool. Cropland is an important highly managed component of the biosphere. Among the many managed components of cropland is the production nof crop residue, use of tillage systems to control crop residue placement/disturbance, and residue decomposition. An accumulation of SOC is a C sink (a net gain from atmospheric CO2) whereas a net loss of SOC is a C source to atmospheric CO2. A simple three components model was developed to determine whether or not conservation tillage systems were changing cropland from a C source to a C sink. Grain/oil seed yields and harvest indices indicate a steadily increasing supply of crop residue since 1940, and long-term field experiments indicate SOC storage in no- tillage>non moldboard tillage>moldboard tillage systems. According to adoption surveys, moldboard tillage dominated until about 1970, but non moldboard systems are now used on at least 92 percent of planted wheat, corn, soybean, and sorghum nationally. Consequently, cropland agriculture has become a C sink since about 1980. Moldboard plow systems had prevented a C sink response to increases in crop residue production that had occurred between 1940 and 1970. The model has not only facilitated a qualitative conclusion about SOC, but it can also be used to project production, as well as soil and water conservation benefits, should there be a C credit or payment to farmers associated with the C sink in cropland agriculture.