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| Titel |
Contrasting effects of deep ploughing of croplands and forests on SOC stocks and SOC bioavailability |
| VerfasserIn |
Viridiana Alcántara, Axel Don, Lars Vesterdal, Reinhard Well, Rolf Nieder |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250128430
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| Publikation (Nr.) |
 EGU/EGU2016-8418.pdf |
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| Zusammenfassung |
| Subsoils are essential within the global C cycle since they have a high soil organic carbon
(SOC) storage capacity due to a high SOC saturation deficit. However, measures for
enhancing SOC stocks commonly focus on topsoils. We assessed the long-term stability
of topsoil SOC buried in cropland and forest subsoils by deep ploughing. Deep
ploughing was promoted until the 1970s for breaking up hardpan and improving soil
structure to optimize crop growth conditions. In forests deep ploughing is performed
as a site preparation measure for afforestation of sandy soil aiming at increasing
water availability in deeper layers and decreasing weed competition by burial of
seeds.
An effect of deep ploughing was the translocation of topsoil SOC into subsoils, with a
concomitant mixing of SOC-poor subsoil material into the “new” topsoil horizon. Deep
ploughed croplands and forests represent unique long-term “in-situ incubations” of SOC-rich
material in subsoils in order to assess the effect of soil depth on SOC turnover. In this study,
we sampled soil from five loamy and five sandy cropland sites as well as from five sandy
forest sites, which were ploughed to 55-127 cm depth 25 to 53 years ago. Adjacent, equally
managed but conventionally ploughed or not ploughed (forests) subplots were sampled as
reference.
On average 45 years after the deep ploughing operation, at the cropland sites, the deep
ploughed soils contained 42±13 Mg ha−1 more SOC than the reference subplots down
to 100 cm depth. On the contrary, at the forest sites, the SOC stocks of the deep
ploughed soils contained 18±9 Mg ha−1 less SOC compared to the reference soils
on average 38 years deep ploughing. These contrasting results can be explained,
on the one hand, by the slower SOC accumulation in the newly formed topsoils
of the deep ploughed forest soil (on average 48% lower SOC stocks in topsoil)
compared to the croplands (on average 15% lower SOC stocks in topsoil). On the other
hand, the buried topsoils at the forest sites exhibited similar bioavailability of SOC
(measured as net C mineralization rates from short-term in-vitro incubations) as
compared to the reference topsoils. In contrast, at the sandy cropland sites, net C
mineralization rates were significantly lower (67%) in the buried topsoil material
compared to the reference topsoil. Buried SOC in the sandy soils is thus highly
stable.
Together with these results, we will present data on SOC fractions and discuss their
implications for our view on stability of buried SOC in croplands and forests. Our results
show that deep ploughing contributes to SOC sequestration by enlarging the storage space for
SOC-rich material but only under the preconditions that i) burial is accompanied by decrease
in SOC bioavailability and ii) SOC accumulates considerably in the newly formed topsoil. |
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