## 4 Discussion
By assuming a CT-Wa, CT-Wh2 and CT-M3 distribution at a dose of 300 L year\({}^{-1}\) for a medium period of 10 years, the total heavy metals applied to the soil are extremely low and well below the maximum annual quantities allowed by Legislative Decree No. 99, 27/01/1992 concerning the disposal on land of sewage sludge (application of 5 t ha\({}^{-1}\) year\({}^{-1}\) of sewage sludge--on a dry matter basis) [41] (Table 9). Although total heavy metal contents in the experimental CTs were low, an increase of their bioavailable forms (ionic and chelated forms, presence in microorganisms) should be taken into account. In addition, the distribution on soil of acid or/and chelating products by CTs, could increase the bioavailability of heavy metals, especially in the case of several annual distribution cycles and of medium-long term treatments. Here, CTs exhibited a broad-spectrum of suppressive properties against the tested plant pathogens, interestingly, only when, independently from the concentration, they are used as raw. This means that pathogen containment was mainly due to the microbial components, probably responsible of antagonistic functions [42]. Actually, plate counts retrieved microbial populations, such as _Pseudomonas_ spp. and _Bacillus_ spp., associated to \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Element** & **CT-Wa** & **CT-Wh2** & **CT-M3** & **Maximum Annual Amounts Allowed by the** \\ \hline  & & **g ha\({}^{-1}\)** & & **Italian Law** \\ \hline Fe & 5.6 & 10.1 & 7.3 & - \\ Cu & 0.6 & 3.5 & 0.6 & 5000 \\ Zn & 1.0 & 1.3 & 1.4 & 12,500 \\ Mn & 0.5 & 5.7 & 0.8 & - \\ Cr & 0.7 & 0.1 & 0.1 & - \\ Cd & 0.0 & 0.0 & 0.0 & 100 \\ Ni & 0.1 & 0.2 & 0.3 & 1500 \\ Pb & 0.1 & 0.2 & 0.2 & 3750 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Total heavy metals applicable to the soil in the medium period (10 years) by means of CT-Wa, CT-Wh2 and CT-M3 (300 L year\({}^{-1}\)). Comparison with the maximum annua1 amounts allowed by the Italian law (Legislative Decree, No. 99, 27/01/1992) through the application of 5 t ha\({}^{-1}\) year\({}^{-1}\) of sewage sludge—on a dry matter basis. the biological control of plant pathogens [43; 44]. As expected, additives modulated both the structure and composition of CT communities: molasses stimulated microbial shifts more than whey, likely due to sugar content. Nevertheless, the kind of additive did not univocally affect _Rhizoctonia_ disease control efficacy, likely due to the high suppressive levels just showed by the non-amended tea. Interestingly, additive used at the higher dosage, reduced the suppressivity performances of the formulate suggesting strong effects on the microbial community composition. A literature survey showed how additives might have a role in suppressive functionalities and have a potential to help the definition of the systematic production of CTs suitable for plant disease management [5]. [PERSON] et al. [45] pointed up as an aerated CT added with molasses sourced from oil palm, was able to suppress _Grammothele lineata_ on the Malaysian plant _Melicope ptelefolia_. CTs have a great potential to suppress both air and soil-borne pathogens [46], as also indicated here by the in vitro and in vivo experiments. In a previous assay, where CTs significantly reduced disease symptoms of _Alternaria alternata_, _Botrytis cinerea_ and _Pyrenochaeta lycopersici_ on tomato, suggesting a suitability of the extracting solution for suppressive CTs production [42]. CTs may explicate the biocontrol action against plant diseases through the typical antagonistic mechanisms operated by the resident microflora, including antibiosis, competition for the space and/or for the nutrients, hyperparasitis and induction of systemic resistance in the plants. Microbial biodiversity in the compost is crucial for the suppressive properties [47] that can be transferred into CT.