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Fig. 1. (A) Total CO2 emissions for about 3 wk after adding cowpea residue, and (B) residue-derived and soil-derived CO2 emissions from residue-added cylinders; NT = no-till, ST = standard tillage, +Res = residue added, –Res = no residue added, Row = cores taken from plant row, Ctr = cores taken from the bed center, Int = cores taken from intermediate position between the plant row and the bed center, C = control (residue without soil). In (A), on each date, NS indicates no statistical differences for residue-added treatments, including control, while ns refers to comparison of treatments with no added residue. (Note that for the latter, emissions were significantly higher in NT –Res/Row than in ST –Res/Int on Day 1, and in both NT treatments than ST on Day 7 after watering.) In (B), statistical differences were compared with residue-added CO2 emissions including the control, and are expressed by a or b at each date separately; ns indicates no statistical differences among treatments. There are no data at Day 18 because there was no significant relationship between 
13C of CO2 and 1/41 µmol m–3–CO2. The error bar shows the standard error. Estimates of soil-derived CO2 were calculated using the equation Qs = Qt – Qc, where where Qs = CO2 derived from soil, Qt = total amount of CO2 emitted, and Qc = CO2 derived from residue. Thus, statistical differences are not shown.
