## 3 Results and Discussion
### Evaluation of the Total Antioxidant Capacity (TAC) of Hydroalcoholic Extracts  
Based on the considerations outlined in Section 2, it was decided that the three assays FRAP, ABTS, and DPPH be applied to the eight extracts obtained from the corresponding samples of the three species under study. Each of the 24 extracts was analyzed in triplicate. The main insight from the analysis is that each plant species studied has an optimal set of cultivation conditions that can maximize the total antioxidant capacity of its hydroalcoholic extract. In Table S1, the results from ANOVA test were shown to assess the statistically significant differences among the parameters studied. \begin{table}
\begin{tabular}{c c c} \hline
**DFS** & **BBCH Code** & **Description** \\ \hline
0 & 0 & Germination—Dry seeds \\
7 & 9 & Germination—Emergence of cotyledons break through soil surface \\ \hline
21 & 16 & Leaf development—Six true leaf \\ \hline
34 & 30 & Steam elongation- Start of steam elongation \\
42 & 33 & Steam elongation—Three visible nodes \\
67 & 39 & Steam elongation—nine or more visible nodes \\ \hline
76 & 43 & 30\% of maximum biomass reached \\
90 & 47 & 70\% of maximum biomass reached \\
97 & 49 & 90\% of maximum biomass reached \\
105 & 53 & Inflorescence emergence—Flower buds enlarged; petals visible \\ \hline
110 & 60 & Flowering—Beginning of anthesis: First open flower \\
116 & 62 & Flowering—20\% of flowers open \\ \hline \end{tabular}
\end{table} 
Table 4: BBCH phenological scale of _Trifolium pratense_ with days following sowing (DFS). For _Silybum marianum_ (SM), the hydroalcoholic extract with the highest total antioxidant capacity was obtained under conditions that included the presence of PGPR, no fertilization with P\({}_{2}\)O\({}_{5}\) and K\({}_{2}\)O, and full irrigation at field capacity (conditions SM101: FRAP = 39.39 \(\pm\) 1.59 mg TE/g extract; DPPH = 31.50 \(\pm\) 0.80 mg TE/g extract; ABTS = 45.55 \(\pm\) 0.91 mg TE/g extract, Table 5). In contrast, the extract with the lowest total antioxidant capacity was obtained from plants grown under similar conditions but with irrigation at 40% relative soil moisture (conditions SM100: FRAP = 16.07 \(\pm\) 1.28 mg TE/g extract; DPPH = 9.34 \(\pm\) 0.38 mg TE/g extract; ABTS = 34.55 \(\pm\) 1.62 mg TE/g extract, Table 5). Notably, the generally higher values observed in the ABTS assay compared to the DPPH  
Figure 3: Phenological phases duration expressed in days (d) following sowing (DFS) and corresponding GDD amount requirements. assay suggest that both polar and non-polar compounds contribute to the total antioxidant capacity of the hydroalcoholic extract, acting through both the single electron transfer and hydrogen atom transfer mechanisms. The significant contribution of compounds operating via the single electron transfer mechanism is further supported by the relatively high values obtained in the FRAP assay (Figure 4). Somewhat converging information regarding the optimization of the total antioxidant capacity of extracts from _Achillea millefolium_ (AM) was obtained using the three spectrophotometric assays (Figure 4). Specifically, it appears that the antioxidant power of hydroalcoholic extracts of this species can be mostly enhanced in the presence of PGPR, with fertilization using P\({}_{2}\)O\({}_{5}\) and K\({}_{2}\)O, and under full irrigation at field capacity. For only the DPPH assay, the best combination was the absence of PGPR, the presence of fertilization, and a restricted irrigation regime at 40% of field capacity (condition AM111: FRAP = 107.31 \(\pm\) 3.66 mg TE/g extract; ABTS = 64.74 \(\pm\) 7.80 mg TE/g extract; AM010: DPPH = 30.02 \(\pm\) 1.41 mg TE/g extract, Table 5). Moreover, findings indicate that the antioxidant capacity of the extract is predominantly driven by polar compounds, which exhibit their reducing power through a single electron transfer mechanism, as indicated by the exceptionally high values obtained with the FRAP assay.