Mineralization of Carbon-14-Labeled Plant Residues in Conventional Tillage and No-Till Systems
2013
Sharifi, Mehdi | Zebarth, Bernie J. | Burton, David L. | Drury, Craig F. | Grant, Cynthia A.
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 (MB¹⁴C) 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.
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