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| Titel |
Conversion of cropland to grassland: increasing or decreasing soil organic carbon? |
| VerfasserIn |
Christof Ammann, Jens Leifeld, Pierluigi Calanca, Albrecht Neftel, Jürg Fuhrer |
| 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 |
250041386
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| Zusammenfassung |
| Conversion of cropland to permanent grassland is often expected to sequester atmospheric
CO2 by increasing soil organic carbon (SOC) stocks. We investigated this possibility under
realistic management conditions on the field scale. We compared the development of the
carbon (C) balance and SOC stocks of intensively (high nitrogen input and frequent
cutting) and extensively (no nitrogen input, infrequent cutting) managed grassland
after conversion from an arable rotation. The study was carried out at a site in the
northern lowlands of Switzerland with a temperate climate and a soil classified as
Eutri-Stagnic Cambisol. As a first approach, C balance was assessed by measuring
C fluxes in and out of the ecosystem including net CO2 exchange by eddy flux
measurements, as well as C import by organic fertilizer and C export by harvest. In a second
approach, SOC stocks (0-45 cm depth) were quantified at the beginning (2001)
and at the end (2006) of a 5-year observational period. An equivalent soil mass of
500 kg m-2 was sampled. Results showed very similar SOC stocks in 2001 of
13-14 kg C m-2 for the intensive and extensive field. Over the 5-year period, the
observed mean annual increase for the intensive field was small and not significant,
whereas for the extensive field a significant decrease of 0.22 kg C m-2 yr-1 was
found. The other approach (flux budget) also indicated a generally positive carbon
balance (C accumulation) for the intensive field and a negative balance (C loss) for
the extensive field, with substantial inter-annual variations in relation to growing
season length and soil moisture. Both, stock and flux measurements, revealed a
consistent difference between the C balance of the two management types (about
0.25 kg C m-2 yr-1), which also appeared in simulations with the mechanistic
grassland model PROGRASS. However, absolute values for the C balance differed
between the two experimental approaches. The flux measurements indicated higher
gains to the intensive management, whereas the stock approach suggested larger
losses due to extensive management. It can be concluded that without continuous
nitrogen input, the conversion from arable rotation to permanent grassland may cause
a considerable loss of SOC due to increased soil organic matter decomposition. |
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