The LIFS data (Fig. 2) showed an up to 47% increase in thehumification degree (HFIL) along the depth profile for all treatmentsconsidered. Statistically significant differences were observed(p<0.05) for all cover crop and weed control methodsconsidered, with lower HFIL in surface layers (0–10 cm) than atlower depths. According to González-Pérez et al. (2007), whenplant residues accumulate in the topsoil in high quantity theincidence of less humified (aromatic/condensed) structures isexpected, due to decreased microbial capacity to metabolize thisfresh input and to possible incidence of unprocessed plantmaterial. Thus, the data observed may reflect a higher incidenceof labile structures in surface layers, compared to deeper layers,regardless of cover crop or weed control method used. At leastthreemajor factors ofOMstabilization have been proposed, but therelative contribution of each factor to C protection in soils isunknown (Six et al., 2002): (1) physical stabilization due toestablishment of physical barriers between microbes and enzymesand their substrates as aggregates form (Six et al., 2004); (2)chemical stabilization, referring to the intermolecular interactionsbetween organic and inorganic substances that decrease theavailability of the organic substrate due to complexation offunctional groups and changes in conformationand (3) recalcitrance, referring to the preservation ofOM caused by structures inherently stable against biochemicaldecay such as condensed and lignin-derived aromatic carbons,melanoidins, some tannins or aliphatic compounds (Poirier et al.,2003). Hence, our results may also reflect a higher incidence ofmore physically and chemically protected structures in deeperlayers, related to the humification process, also suggesting a morecondensed/aromatic character for the organic matter. Whenanalyzing each set of cover crop and weed control methods ateach given depth increment, we observed no statistically significantdifferences among treatments (p > 0.05).
การแปล กรุณารอสักครู่..