|Allmaras, Raymond - USDA-ARS RETIRED|
|Molina, Jean - UNIV. OF MINNESOTA|
Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 28, 2005
Publication Date: September 1, 2006
Citation: Dolan, M.S., Clapp, C.E., Allmaras, R.R., Baker, J.M., Molina, J. 2006. Soil organic carbon and nitrogen in a Minnesota soil as related to nitrogen, tillage, residue and nitrogen management. Soil & Tillage Research. 89:221-231. Interpretive Summary: Tillage and residue management practices which conserve soil organic carbon have been in practice for several decades, resulting in a near equilibrium of carbon gains and gaseous losses. Early studies found more organic carbon in surface soils with conservation tillage and residue practices than in conventionally plowed surface soils. This research indicates that when taking subsurface soils into account, organic carbon did not vary in the soil profile as a whole when comparing conservation and conventional tillage and residue management practices. Both agricultural producers and environmental planners can use these results to more clearly evaluate potential carbon accumulation resulting from conservation management practices, as well as how differing sampling methods can lead to different conclusions about soil carbon storage.
Technical Abstract: Soil organic carbon (SOC) and nitrogen (N) are directly influenced by tillage, residue return and N fertilization management practices. Soil samples obtained from long-term field experiments for SOC and N analyses provided an assessment of near-equilibrium SOC and N conditions. Treatments of conventional and conservation tillage, residue stover (returned or harvested), and two N fertilization rates were imposed on a Waukegan silt loam (fine-silty over sandy or skeletal, mixed, superactive, mesic Typic Hapludoll) at Rosemount, MN. The surface (0 to 20 cm) soils with no-tillage (NT) had greater than 30% more SOC and N than moldboard plow (MB) and chisel plow (CH) tillage treatments. The trend was reversed at 20 to 25-cm soil depths, where significantly more SOC and N were found in MB treatments (26 and 1.5 Mg SOC and N ha-1, respectively) than with NT (13 and 1.2 Mg SOC and N ha-1, respectively), possibly due to residues buried by inversion. The summation of soil SOC over depths did not vary among tillage treatments; N by summation was higher in NT than MB treatments. Residue-returned generally stored more SOC and N than in plots where residue was harvested. Nitrogen fertilization generally did not influence SOC or N at most soil depths. These results have significant implications on how specific management practices maximize SOC storage and minimize potential N losses. Our results further suggest different sampling protocols may lead to different and confusing conclusions regarding the impact of tillage systems on C sequestration.