|18th World Congress of Soil Science
July 9-15, 2006 - Philadelphia, Pennsylvania, USA
In March 2005, soil samples were collected (depth: 0-20 cm) from organically and conventionally managed fields at two sites located in central Italy (“Colle Valle Agrinatura” and “La Selva”), one site located in Switzerland (DOK-trial) and one site located in south of Germany (Scheyern). We analysed the C mineralization of the soils during a 90-days incubation experiment. Before and at the end of this incubation experiment, we measured water extractable organic carbon, recorded fluorescence emission spectra of the water extracts in order to calculate a humification index (HIXem). Furthermore, we measured the biodegradability of WEOM in the extracts before soil incubation.
Organically managed soils contained more water-extractable organic C than conventionally managed soils except for the site “Scheyern”. C mineralization was larger for the treatment with larger contents of WEOC at all sites. That means, the size of the water extractable organic matter pool correlated very well with C mineralization from the soil. Furthermore, a higher C mineralization occurred only in the organically managed soils if they had a larger content of WEOC than the conventionally managed fields.
Table 1: WEOC content of the soils, percentage of WEOC in total organic C (TOC) of the soil and loss of C by CO2 during a 90 day incubation experiment (as % of TOC of the soil; mean and standard error of 6 replicates)
We conclude that the size of WEOM is important in regulating C mineralization from soils. Small differences in the composition of this labile C pool, as indicated by the HIXem and its biodegradability are not reflected in a changed C mineralization from the soil.