RELATIONSHIP BETWEEN SOIL WATER CONTENT AND CARBON-DIOXIDE EMISSION IN
DIFFERENT SOIL MANAGEMENT SYSTEMS
Eszter Toth, Sandor Koos
Research Institute for Soil Science and Agricultural Chemistry of HAS,
Herman O. Str. 15, Budapest, 1022, Hungary; e-mail: teszter@rissac.hu
The terrestrial ecosystems are the biggest carbon reservoirs on the earth. Soils, as part of these
ecosystems, play a very important role in the global carbon cycle. It was proved, that a considerable
part of the atmospheric carbon pool came from the terrestrial ecosystems, especially from soils (Lal, R
et al. 1998). Globally, the agricultural originated carbon getting into the atmosphere is estimated at
2.5x1015g. This loss has an effect not only on the global warming, but plays an important role in the
long-term quality of soils (Bloodworth and Uri, 2002).
Land use, land use changes and forestry are some of the most important factors controlling or
affecting the carbon cycle and have a great impact on the exchange of CO2 between terrestrial
ecological systems and the atmosphere. Soil carbon sequestration could be increased by applying
appropriate land use and agricultural practices resulting in reduced loss of soil organic carbon and
increased humification rate (Nemeth, 2004). Consequently, the balance must be found between the
highly disturbed and the non-tillage cropping systems applied in agriculture to ensure the least
possible carbon losses from soils (Nemeth et al., 1998). This requires proper information on the effects
of various soil management systems on soil carbon cycle elements, especially on soil carbon dioxide
emission.
Regardless to its importance, there are no harmonised and standardised methods to measure the
carbon dioxide emission from soils. Measurements performed at different sites or at the same site but
different circumstances are difficult to compare due to strong dependency of the results on soil water
content, soil temperature, soil organic matter content and bulk density. Hence, development of soil
carbon-dioxide emission measurement methods and their application for samples taken from different
soil management systems still call for further attention.
Soil carbon-dioxide emission measurements have been carried out in RISSAC since 2003. In the
beginning of the investigation, soil carbon-dioxide fluxes were measured only in situ in a long-term
fertilization- and tillage experiment in order to investigate the effect of various soil management
practices on soil carbon sequestration. Field measurements, however, are expensive and time
consuming. Additionally, several problems can occur during their execution. Our works were often
obstructed by the weather or surface (e.g. pounding water) conditions as well as field works carried
out. Moreover, in CO2 emission calculations it was extremely difficult to account for changes in air and
topsoil temperature observed during the incubation, and to separate the effect of different soil
management practises from that of air temperature and soil water content.
To avoid the above-mention holdbacks, in 2008 carbon-dioxide measurements were started in
RISSAC under laboratory conditions. The measurements were carried out on undisturbed soil samples
in a climatic room with a constant air temperature of 21oC. 10-centimeter-high undisturbed soil
samples were taken in 20-centimeter-high PVC tubes. 28 samples were collected from three different
tillage treatments: ploughing, direct drilling and disking combined with deep loosening. In the
laboratory, different amounts of water (0, 50 ml, 100 ml, 150 ml) were added to the samples (that
correspond to rainfall of 0, 6.38, 12.76 and 19.14 mm), so soil carbon fluxes could be measured at four
different soil water content levels in seven replicates. Air samples were taken from above the
incubated soil samples once a week after three-hour-long incubation during three months. The
samples were analysed using a gas chromatograph. The circumstances of the experiment were set on
such a way so that the effect of air temperature and changes in soil water content on carbon-dioxide
emission could be eliminated.
This paper introduces the soil carbon dioxide emission measurement method, developed in RISSAC
and discusses the measurement results, obtained from different management systems.
Keywords: soil carbon-dioxide fluxes, soil water content