## 4 Discussion  
In this study a quality commercial compost, suitable for use in organic agriculture as an amendment, was used to obtain CTs brewed with the addition of whey and molasses. These two by-products of the food transforming chain were used as additives, at different concentrations, to provide feeding sources for CT microbial populations. The chosen additives showed different chemical characteristics (i.e., molasses had higher pH values, N and heavy metal concentrations than the whey, which had greater TOC content), which supposedly affected the quality of the produced CTs, together with  
Figure 4: Phytotoxicity assays on seeds of _Solanum Lyopersicum_ L. (tomato), _Cucumis sativus_ L. (cucumber) and _Lepidium sativum_ L. (cross) treated with the different CTs (1:3 \(v\bar{v}\), CT: water) sampled after 24 (**a**) and 48 h (**b**) from the start of the extraction process. Lowercase letters indicate statistically significant differences (\(p\leq 0.05\)) within the same sampling time. the applied doses and the duration of the extraction process. In particular, a 48 h-extraction duration was chosen with an intermediate sampling at 24 h, with the aim to cover the optimal brew time range and to observe maximum microbial activity in CTs [17]. The combination of the different starting feedstock (compost and additives) influenced pH and EC of CTs during the extraction process. This in accordance with what found by [PERSON] et al. [30] after 2-day incubation of four types of aerated CTs. The low pH values showed by the whey CTs, especially after 24 h, could have an acidifying and potentially toxic effect on crops and increase the availability for absorption of heavy metals into the soil. Furthermore, the low pH of the whey CTs could accelerate irrigation system corrosion in fertigation applications. Conversely, a gradual increase of pH was shown by the CTs made using molasses, evidently due to its alkaline pH values. As reported by [PERSON] [31], pH can strongly affect development of the microbial population. Acid pH measured in whey CTs probably favored growth of the fungal populations with respect to the bacterial groups. [PERSON] et al. [32] assessed the biostimulating properties of a fermented whey putatively associated to lactic acid, peptides, and free amino acids, with the further effect to lead microbial changes towards biocontrol active populations. EC values in the experimental CTs, ranging from 4.45 to 8.20 mS cm\({}^{-1}\) (Table 4), were well over the maximum threshold indicated for an irrigation water acceptable and usable without restriction [33], suggesting the need of the CT's dilution. [PERSON] et al. [30] recorded significantly increased EC values of aerated CTs sampled after 1-day incubation, resulting in phytotoxic effects on cress seed germination, a species known to be highly sensitive to salt stress. In the current work, cress GI was negatively correlated to CTs electrical conductivity in both sampling points. An inverse behavior was observed on tomato seeds, which showed increased germination when treated with the CTs sampled after 48 h. This finding suggests further investigations on such a germination response. With respect to the CTs dilutions, it seems that the best compost-to-water ratio for agronomical utilization was 1:4 for all the CTs produced. Such ratio assured EC values ranging from 1 to 2 mS cm\({}^{-1}\), which can be suitable for crop fertigation. The suitability of CTs for soil treatment can be evaluated by means of both salt amounts and salt quality (especially the ratio among cations, Na\({}^{+}\), Ca\({}^{2+}\), Mg\({}^{2+}\), in solution). SAR indicates sodium activity in CTs and how it can participate in the exchange process, which occurs in the soil in antagonism with calcium and magnesium. SAR showed by the CTs in comparison falls within the usual range in irrigation water [33].