We suppose that the decrease in total organic C in the compost
mixtures observed mainly in the coarse fractions (Fig. 3) during the
first year (between T5 and T12) was due to degradation mechanisms
linked to biological activity. We did not, in fact, measure the migration
of organic matter in the deep layer, nor losses due to leaching. In the
coarse fractions (N1 mm) and intermediary (0.2 to 1 mm) particles,
the quantity of organic matter decreases either by physical fragmentation
or by mineralisation. In the fine fractions (b0.2 mm), organic
matter accumulates faster than it breaks down.
During its decomposition, organic matter becomes increasingly
stable (Chefetz et al., 2002) and, therefore, more resistant to degradation
as a result of its biochemical nature (Dignac et al., 2006). The organic