Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 11/5/2000
Publication Date: N/A
Technical Abstract: Soil samples were taken from a long-term experiment on tillage, residue and N management representing 13 yr of continuous corn (C4) followed by 4 yr of soybean (C3). Tillage treatments were no-till (NT), chisel plow (CH) and moldboard plow (MB); residue treatments were residue returned (r) and residue harvested (h). Samples were taken at 5-cm depth increments to 30 cm and 15-cm depth increments from 30 to 90 cm. They were analyzed for soil organic C (SOC) and 13C to separate current C from relic C. Current C is the SOC derived from soybean and relic C is the SOC derived from previous vegetation or crop before the start of continuous soybean. The contribution of soybean to SOC ranged from 0 to 26%. Appreciable contribution occurred at the 0- to 5-cm depth when residues were returned under NT (about 26%) and CH (about 20%). Under MB, the measured contribution of soybean in the upper 25 cm was <5%; however, at the 25- to 30-cm depth the contribution was (>10%). Except for the very surface of NTr and CHr and at the 25- to 30-cm depth under MB, the SOC within the profile was predominantly relic C.