World Congress of Soil Science Logo 18th World Congress of Soil Science
July 9-15, 2006 - Philadelphia, Pennsylvania, USA
International Union of Soil Sciences

Monday, 10 July 2006 - Friday, 14 July 2006
162-18

This presentation is part of 162: 4.1A Organic Farming – Advantages and Disadvantages for Soils, Water Quality and Sustainability - Poster

Effects of Organic Farming on the Labile Carbon Pool in Soils.

Katia Liburdi, Dept Agrobiology and Agrochemistry, Univ of Tuscia, via S. Camillo de Lellis, Viterbo, 01100, Italy, Karsten Kalbitz, Univ of Bayreuth, Dept of Soil Ecology, Dr.-Hans-Frisch-Str. 1-3, Bayreuth, D-95440, Germany, Sara Marinari, Dept Agrobiology and Agrochemistry, Univ of Tuscia, via S. Camillo de Lellis, Viterbo, 01100, Italy, and Stefano Grego, Dept Agrobiology and Agrochemistry, University of Tuscia, via S. Camillo de Lellis, Viterbo, 01100, Italy.

Water-extractable organic matter (WEOM) is involved in many soil processes although it represents only a small part of soil organic matter. Land use and management practices affect soil properties, and thereby are likely to influence the WEOM pool. In many studies organic management resulted in an immediate and significant increases of water-extractable organic C (WEOC) because of the direct addition of water soluble organic matter and the stimulated microbial activity after the frequent use of animal manure and mechanical weed control. The objective of this study was to evaluate the impact of organic and conventional managements on the amount and composition of WEOM. We wanted to know whether water extractable organic matter could be considered as a reliable parameter for labile organic matter in soils.

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.


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