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control after 30 yrs (+ 6%). This behaviour further confirms the positive role of the humic
fraction in C sequestration and storage. The quality of this humic fraction was also affected
by the different agricultural practices, so that when the soil did not receive any amendment,
the aromatic and carboxylic C decreased, whereas the aliphatic C increased as an effect of the
crop rotation. With the amendments, in contrast, the aromatic C generally increased, but with
CR this increase was mainly due to preservation of undecomposed lignin components derived
from the crop-residues added to the soil, whereas with CM, this kind of C was the result of a
new synthesis of HS. The presence of a high amount of carboxylic groups, highly substituted
aromatic and alkyl-C components further supports this idea. The study of the effects of
different agricultural practices on SOC dynamics in the long run is very important in order to
achieve a sustainable agriculture. This research provided additional evidence of the important
role played by amendment practices on soil HA formation and on the ability of HS to
sequester C.
A
CKNOWLEDGEMENTS
This research was supported with funds provided by i) the “Ispettorato Centrale delle
Repressioni Frodi” of the Italian Ministry of Agricultural and Forestry Politics, ii) University
of Bologna (ex quota 60% - 2006) Thanks are due, in particular, to Prof. G. Toderi and Dr. G.
Giordani for supplying the samples
R
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