Submitted to: International Humic Substances Society Conference
Publication Type: Proceedings
Publication Acceptance Date: 10/23/2000
Publication Date: N/A
Interpretive Summary: The influence of tillage and crop residue management on carbon storage in US croplands can have a major impact on global warming. Long-term field experiments, however, are needed to project carbon storage amounts and controlling conditions. In a 19-year field experiment with 13 years of continuous corn, followed by 6 years of soybean, it was shown that nitrogen nfertilization, corn residue (stover) management, and tillage system all significantly influenced the carbon cycle and carbon storage in the soil of a semi-humid climate in the northern portion of the Corn Belt. This information will be used by scientists and extension specialists to provide a basis for the potential reduction of atmospheric carbon dioxide related to cropland agriculture.
Technical Abstract: Differences in natural abundance 13C between C-3 and C-4 plants can be used as an in situ label of soil organic matter (SOM). A long-term experiment was carried out at Rosemount, MN involving tillage, residue and N management on a Typic Hapludoll soil where corn (C-4) was grown continuously for 13 years. Changing the crop to soybean (C-3) for 6 years provided an opportunity for organic C and 13C studies. The objectives wer to show the distribution of soil organic carbon (SOC) and 13C with soil depth and to compare this depth distribution to adjacent uncultivated prairie, low input grass, and non-vegetated fallow sites. Soil samples were taken from the experimental plots in 1993 (after 13 years of corn), and in 1997 (after 4 years of soybean) at 5-cm depth increments down to 30 cm and 15-cm depth increments to 90-cm depth. In 1999, soil samples were taken from the same experiment down to 30 cm. Soil samples were analyzed for SOC and 13C using an elemental analyzer (Carlo-Erba) and a stable isotope ratio mass spectrometer (Optima) continuous flow system. The distribution of SOC with depth from 1993 to 1997 showed decreasing SOC, however, there was a zone, at 20 to 40 cm, where the decrease was relatively sharp. Distribution of 13C with depth showed that the isotope C increased with depth, however, at depths greater than 45 cm there was a tendency for 13C to decrease. Decreases in SOC and 13C in the surface soils were appreciable with residues returned, especially under no-till and chisel plow.