Mineralization of carbon-14-labeled plant residues in conventional tillage and no-till systems

Tillage systems are known to influence the quantity and quality of soil organic C (SOC); however, it is unclear if tillage also changes the soil catabolic capacity (the ability to decompose C substrates). This study compared soils from two contrasting tillage systems, no-till (NT) vs. conventional tillage (CT), with respect to their ability to catabolize a common 14C-labeled substrate. Intact core samples from the 0- to 5-cm soil depth under CT and the 0- to 5- and 10- to 15-cm depths under NT were collected after 14 yr of winter wheat (Triticum aestivum L.)-corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation. Soil cores received a common substrate ( 14C-labeled wheat residues) either surface applied or incorporated into the soil. Decomposition of the 14C-labeled residues, soil mineral N concentration, and soil microbial biomass 14C (MB 14C) were monitored for 86 d at 25°C. Respiration of 12CO2 from native SOC was greater at 0 to 5 cm under NT than CT but did not vary with depth under NT; there was no significant effect of tillage system or depth under NT or residue placement on respiration of residue 14CO2. Incorporation of 14C residues increased MB14C compared with surface application, indicating a greater efficiency of C utilization. For the soils and residues used in this experiment, there was no evidence of an effect of tillage system on soil catabolic capacity, and differences in soil microbial activity between tillage systems were attributed only to differences in the quantity and quality of C substrates. © Soil Science Society of America.