Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 10/1/1999
Publication Date: N/A
Technical Abstract: Soil samples were taken from a long-term experiment on tillage, residue, and nitrogen management representing 13 yr of continuous corn (C4) followed by 4 yr of soybean (C3). Samples were taken at 5-cm depth increments down to 30 cm and 15-cm depth increments at deeper depths down to 90 cm. They were analyzed for soil organic C (SOC) and delta **13C to determine the differences due to crop change. No-till treatments, especially with residues returned, exhibited the strongest effect on SOC concentration and delta **13C values as a result of crop change; SOC and delta **13C both decreased at the 0- to 10-cm depth after 4 yr of soybean. Chisel treatments exhibited little or no change in SOC, but a substantial change in delta **13C at the 0- to 20-cm depth. Plow treatments showed little or no effect in either SOC or delta **13C. With increasing soil depth, regardless of the treatments, the concentration of SOC decreased while delta **13C increased; ;the change was abrupt at 20 cm down to 45 cm. However, at depths greater than 45 cm the delta **13C values tended to decrease.