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| Titel |
Modeling impacts of management alternatives on soil carbon storage of farmland in Northwest China |
| VerfasserIn |
F. Zhang, C. Li, Z. Wang, H. Wu |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 3, no. 4 ; Nr. 3, no. 4 (2006-10-24), S.451-466 |
| Datensatznummer |
250001158
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| Publikation (Nr.) |
 copernicus.org/bg-3-451-2006.pdf |
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| Zusammenfassung |
| Long-term losses of soil organic carbon (SOC) have been observed in many
agriculture lands in Northwest China, one of the regions with the longest
cultivation history in the world. The decline of SOC contents not only
impaired the soil fertility but also increased the amount of carbon dioxide
(CO2) emitted from terrestrial ecosystems into the atmosphere. However,
quantifying the SOC losses at regional scale has long been remaining
unsolved. A process-based model,
Denitrification-Decomposition or DNDC,
was adopted in the study to quantify impacts of farming management practices
on SOC dynamics for a selected region, Shaanxi Province. The selected
domain, with 3 million hectares of cropland across different climatic and
farming management regimes, is representative for the major agricultural
areas in Northwest China. The DNDC model was tested against long-term SOC
dynamics observed at five agricultural sites in China. The agreement between
the observed and modeled results indicate that DNDC was capable of capturing
patterns and magnitudes of SOC changes across the climate zones, soil types,
and management regimes in China. To quantify SOC dynamics for Shaanxi, we
constructed a GIS database to hold all of the DNDC-required input
information (e.g., weather, soil properties, crop acreage, and farming
practices) for all the farmland in the studied domain. Sensitivity tests
indicated the spatial heterogeneity of soil properties, especially initial
SOC content, was the major source of uncertainty for the modeled SOC
dynamics at regional scale. The Most Sensitive Factor (MSF) method was
employed in the study to quantify the uncertainties produced from the
upscaling process. The results from the regional simulations for Shaanxi
indicated that (1) the overall 3 million hectares of farmland in the
province was a source of atmospheric CO2 with 0.5 Tg C yr−1 lost
in 2000 under the current farming management conditions, (2) an increase in
the rate of crop residue incorporation from 15% to 50% or 90%
converted the farmland from the C source to a C sink with 0.7 or 2.1 Tg C
yr−1 sequestered, respectively, and (3) applying farmyard manure at a
rate of 500 kg C ha−1 also converted the cropland into a weak C sink
with 0.2 Tg C sequestered in the farmland in Shaanxi. In the studied
domain, crop residue and farmyard manure used to be the major sources of
soil nutrients during the centuries-long cultivation history but were
gradually abandoned since 1950s when synthetic fertilizers became available.
The results from this modeling study suggest that recovery of the
traditional farming practices (i.e., residue incorporation and manure
amendment) be a feasible approach to substantially improve the soil C status
in the farmland of Shaanxi. The values of C gain or loss from this study for
Shaanxi could vary if the modeled domain shifts to other provinces in
Northwest China although the general conclusion may remain. |
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