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 Q_s = Q_t – Q_c, where where Q_s = CO₂ derived from soil, Q_t = total amount of CO₂ emitted, and Q_c = CO₂ derived from residue. Thus, statistical differences are not shown.