Discussion of Results

We have used both bibliographic and original data from the MESCOSAGR project to compare the effects of C sequestration methods on selected biochemical indicators of soil quality, such as enzymatic activities and PLFAs. We found (Tables 7.1-7.6) that much information is available in literature in response to soil treatments such as addition of humified composted matter and different tillage systems, but it has never been summarized and critically evaluated. In the case of the carbon sequestration method based on the catalyst-assisted in situ photo-polymerization of SOM, there are no information yet available on the soil biological responses, and, thus, our results are original, together with those also reported in Chap. 6.

According to literature, some trends were identified for the responses of enzymatic activities to compost addition (Table 7.2), and were even more definite for the responses to tillage (Table 7.3). Based on reports regarding 12 enzymatic activities, these were in most cases induced after addition of different types of compost and manure, at different rates and in different soil types. In some specific cases, no significant differences or inhibitions were found, usually because of presence of contaminants or other compounds, or by the application of too small rates. In response to tillage treatments, the enzymatic activities reported were even clearer in showing a general trend of larger values in no tilled plots (Table 7.3). However, a number of other works indicated that soil organic amendment or reduced tillage had no effects on most enzymatic activities or even resulted in their inhibition. Other soil parameters or management practices (e.g., pest control strategies) were also accounted to play a role on soil biological responses (Omar and Abdel-Sater 2001).

For the MESCOSAGR project, the effects of soil compost amendment and tillage practices were followed on four selected enzymatic activities (p-glucosidase, phosphatase, urease and invertase). The soil treatments were found to hardly have an influence on these enzymes. Specifically, it was found that only the minimum tillage treatment had an effect on urease, p-glucosidase and invertase, and only in the Piacenza site. Neither compost additions nor the biomimetic catalyst spread resulted in significant changes of the four enzymatic activities.

The determination of PLFA values in soil provides indications on the content and changes of different microbial groups (Table 7.3). The soil PLFA patterns were generally altered by compost additions in soil or changes in tillage practices. These alterations lacked, however, a consistent direction, as some microbial groups were found to be either enhanced or reduced, or not affected at all. This variability in literature data was confirmed by results obtained at the third year of experimentation within the MESCOSAGR field trials. These findings showed that some micro-bial groups (Gram-positive, fungi, actinomycetes) changed according to field site and/or soil treatments, while other showed almost constant levels across sites.

A comparison of the third-year values with those obtained after the first experimentation year (data not shown here) suggests that the content of enzymatic activities and PLFAs in MESCOSAGR soils increased after 3 years of treatments, but not in all cases. Specifically, it was found an increase in Piacenza for invertase and urease for the MIN treatment, while enzymatic activities were relatively constant in the other sites, if not even progressively reduced in some cases. Analyses of PLFAs data showed some changes in the global pattern with time, though the trends reported in Table 7.7 and in Figs. 7.6-7.8 were quite constant. These outcomes confirm the variability of these parameters in time, and the importance of carrying out experimentation for some consecutive years in order to identify and confirm specific trends.

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