Fig. 1. Tillage and crop residue effects on soil CO₂ emission after 3 yr in a corn–soybean rotation. Least significant difference (LSD) at P < 0.05 for each measuring time is provided in the graph; NS, not significant at P < 0.05. NTR, no-tillage with residue; NTW, no-tillage without residue; ST, strip-tillage; DR, deep rip; CP, chisel plow; MP, moldboard plow.