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Short-Term Fates of Carbon-13-Depleted Cowpea Shoots in No-Till and Standard Tillage Soils

^a Dep. of Land, Air, and Water Resources, Univ. of California, Davis, CA 95616
^b School of Biological Sciences, Monash Univ., Clayton, 3800, Victoria, Australia
^c Dep. of Nematology, Univ. of California, Davis, CA 95616

View larger version (21K): [in this window] [in a new window]   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.

View larger version (15K): [in this window] [in a new window]   Fig. 2. Microbial biomass C (MBC) at three sampling times at (A) 0- to 5-cm depth and (B) 5- to 15-cm depth; 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 an intermediate position between the plant row and the bed center. Statistical differences were expressed with s and t at 10 d, and x and y at 31 d; NS means no statistical difference among treatments at a sampling time. The error bars show the standard error.

View larger version (17K): [in this window] [in a new window]   Fig. 3. Microbial biomass C (MBC) derived from cowpea residue at 10 and 31 d; NT = no-till, ST = standard tillage, +Res = residue added, Row = cores taken from plant row, Ctr = cores taken from the bed center, Int = cores taken from an intermediate position between the plant row and the bed center. Statistical differences are expressed with a or b and h or i at 0- to 5- and 5- to 15-cm depths, respectively, at 10 d, and with s or t and x or y, respectively, at 31 d. The error bars show the standard error.

View larger version (12K): [in this window] [in a new window]   Fig. 4. Amount of C derived from cowpea residue in nematode biomass C at 31 d; NT = no-till, ST = standard tillage, +Res = residue added, Row = cores taken from plant row, Ctr = cores taken from the bed center, Int = cores taken from an intermediate position between the plant row and the bed center. Statistical differences are expressed with a or b and s or t at 0- to 5- and 5- to 15-cm depths, respectively. The error bars show the standard error.

View larger version (17K): [in this window] [in a new window]   Fig. 5. Nematode biomass C at 31 d; 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 an intermediate position between the plant row and the bed center. There were no statistical differences at 0- to 5-cm depth. Statistical differences are expressed with s and t at 5- to 15-cm depth. The error bars show the standard error.