Fig. 6.5 Coefficient of endogenous mineralization (CEM) of soils sampled from the Napoli (Na) and Torino (To) experimental sites. The values are mean ± SE. TRA conventional tillage, COM-2 compost amendment, MIN minimum tillage. CAT: conventional tillage with addition of biomi-metic catalyst, No-CAT: conventional tillage without catalyst. Different letters indicate significant differences among treatments (ANOVA-Holm-Sidak test; p < 0.05) within site and year their interaction. CEM was always lower in COM-2 than in TRA and MIN for both Napoli and Torino field sites.
The general reduction of AFM, microbial biomass and respiration, for both bulk soil and rhizo soil subjected to COM-2 may be explained by the protection that the humified mature compost exerts on bio labile components of soil. This makes them less bio accessible and thus more resistant to microbial degradation (Spaccini et al. 2002; Piccolo et al. 2004).
Another effect of COM-2 was the increase in soil moisture, compared to TRA and MIN. According to Carter (2007), compost amendment improves soil porosity and consequently favors an increase in soil moisture. For both Napoli and Torino sites, water content in bulk soil for the 2008 experimental year was generally larger than for 2007 (Fig. 6.4), whereas the rhizo soil at Napoli had lower water content than the rhizo soil at Torino. More specifically, soil water content tended to be the highest in compost-amended plots at both sites and in both years.
In addition, no difference was found in microbial biomass in soils subjected to TRA and MIN, with the exception of Torino rhizo soil. This result may indicate that the 3-year treatment period is too short to produce a significant improvement in soil biological quality. In fact, various studies (Joergensen and Castillo 2001; Balota et al. 2003; Franchini et al. 2005; Wright et al. 2008; Helgason et al. 2009) indicate that the effects of different agricultural management on soil microbial communities become evident after longer periods (at least 10 years). Nevertheless, AFM and microbial biomass of rhizo soil in MIN were larger in 2008 than in TRA for the Napoli and Torino sites, respectively.
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