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| Titel |
Soil C saturation does not seem to influence short-term decomposition of maize residues |
| VerfasserIn |
Vincent Poirier, Denis Angers, Philippe Rochette, Joann Whalen |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250038241
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| Zusammenfassung |
| Accumulation of organic C in agricultural soil has the potential to mitigate the increasing
CO2 content of the atmosphere, but as a soil reaches C saturation, its ability to retain
additional organic C might be limited. As such, the amount of clay and silt particles and the
initial organic C content of the soil are believed to influence the decomposition of plant
residues and their stabilization as soil organic C (SOC). A soil with SOC content far
below its theoretical C storage potential (C saturation limit), i.e. a soil having a
high C saturation deficit, would have much capacity to sequester additional C. The
objective of this study was to evaluate, under controlled condition, the effects of soil C
saturation deficit and level of C input on corn residue decomposition in topsoil and
subsoil of a cultivated heavy clay soil from the St. Lawrence lowlands, Eastern
Canada. Comparison of this topsoil and subsoil, which had similar texture (941 g clay
+ silt kg-1 soil) and mineralogy (> 40% illite + chlorite in the clay fraction) but
contrasting SOC contents, should allow for a clear evaluation of the effect of C saturation
deficit on residue decomposition. We incubated topsoil (31.3 g C kg-1 soil) and
subsoil (4.5 g C kg-1 soil) samples with 13C-15N-labelled corn residues at rates
of 0, 2.5, 5, 10, 20, and 40 g C kg-1 soil under laboratory conditions for 51 d.
Temperature, soil moisture content and mineral N concentrations were adjusted to
optimal levels for microbial activity. Whole soil SOC content increased linearly
with increasing residue inputs and both soils responded similarly to increasing C
additions. Such linear accumulation reflects non-saturation behaviour of the whole soil
SOC pool during the short term incubation. The amounts of residue-C stabilized
were not statistically different between the two soils for each residue addition rate,
despite the much greater C saturation deficit in the subsoil than in the topsoil. Even
when the residue C input greatly exceeded the amount that would be added to soils
under field conditions (e.g., > 20 g C kg-1), whole soil SOC (27.2 g C kg-1 soil) in
the subsoil did not reach the theoretical C storage capacity limit. However, the
expected C storage capacity was greatly surpassed in the topsoil (50.0 g C kg-1 soil)
with the same amount of residue-C added. Results presented here do not support
the hypothesis that whole soil C accumulation is limited with respect to residue
C inputs, at least in the short-term. Residue-induced cumulative C-CO2 lost was
positively correlated with the amount of C added and was greater in topsoil than subsoil
within each C input rate. The linear increase in total respiration with application
rates implies that for the 51 d of incubation, no limitation or levelling off of soil
decomposition activity occurred in the topsoil or the subsoil. Despite differences in C
mineralization, similar amounts of residue-C were stabilized in both soils. This suggests that
the increased C mineralization observed in the topsoil could be attributable to the
mineralization of native SOC and thus that a priming effect could have occurred
in our study. However, if a priming effect occurred in the topsoil, its magnitude
was small when compared to the high levels of SOC measured at the end of the
experiment. Soil C saturation deficit did not influence residue-C stabilization in this
study and the linear accumulation of residue-C tends to show that whole soil SOC
accumulation is not limited with respect to C inputs in the short term in this heavy clay
soil. |
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