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SOIL BIOLOGY & BIOCHEMISTRY

Residue Carbon Stabilization in Soil Aggregates of No-Till and Tillage Management of Dryland Cropping Systems

^a Natural Resource Ecology Lab. and Dep. of Soil and Crop Sciences, Colorado State Univ., Fort Collins, CO 80523
^b Dep. of Natural Resources, Univ. of New Hampshire, Durham, NH 03824
^c Dep. of Earth and Atmospheric Science, Purdue Univ., West Lafayette, IN 47907
^d Dep. of Plant Sciences, Univ. of California, Davis, CA 95616

^* Corresponding author (golchin{at}nrel.colostate.edu).

Tillage events have an important influence on residue incorporation into soil profiles and soil aggregate disruption, and ultimately influence the net C gain or loss in soils. Thus, our objective was to evaluate tillage-induced influences on aggregate structure, residue-derived C stabilization, and the subsequent efficiency of C stabilization in aggregates of no-till (NT) and tillage management (TM) practices at different depth increments of the soil profile. Uniformly ¹³C-labeled wheat residues were added to incubation cores representing soils under NT and TM during a year-long in situ incubation at a dryland agriculture experiment site. Residue was added directly onto the surface of NT cores, while residues were incorporated into the 0- to 5-, 5- to 15-, and 15- to 30-cm depth increments of the TM cores. We found that residue additions did not have a significant effect (P > 0.05) on aggregate dynamics in either NT or TM, but NT management did result in the greatest stabilization of residue-derived C (11.2 ± 2.4 g residue C kg^–1 soil kg^–1 residue C added, P < 0.05) in the macroaggregate (>250-µm) fraction of the 0- to 15-cm increment. Residue-derived C stabilization was significantly greater (P < 0.05) in the 0- to 30-cm increment than in the 0- to 15-cm increment of the TM management cores. Overall, our results indicate that, within a plow depth of 15 cm, limiting the tillage-induced disruption of aggregates has a stronger influence on the efficiency of C stabilization than residue incorporation into the profile via tillage. When residues are distributed to a 30-cm depth, however, the negative impact of aggregate disruption through tillage appears counterbalanced, with similar efficiencies of C stabilization between the NT and TM practices, possibly due to slower decomposition of residues deeper in the profile.

Abbreviations: cPOM, coarse particulate organic matter • minM, silt plus clay within macroaggregates • mM, microaggregate-sized fraction within macroaggregates • NT, no-till • SOC, soil organic carbon • SOM, soil organic matter • TM, tillage management