## 3 Results and Discussion
### Effect of EM and OMW Treatments on Plants Growth
The increased growth observed in _Tanacetum basamita_ treated plants, can be attributed to the biostimulants influence and the effect is evident in both the rooting system and the aerial biomass development. In literature, several studies reported on horticultural and ornamental plants, the positive influence of microorganism activity (EM) on plant growth parameters [36; 37; 38; 39]. In Figure 3 the plants at T0 and T3 are shown, with details of leaves and roots. The positive application of EM and OMW resulted also, in an increases in values of leaves number (LN) and leaf area (LA) (Table A4; Figures 3 and 4A,B). The average number of leaves in plants treated with OMW and EM (181.6) enhanced by 78.5% with respect to the Control; the highest values were observed applying the minor biostimulant concentrations, O1 (205 leaves) and in E1 (185.8 leaves) (Figure 4A; Table A4). Control plants registered a mean leaf area of 39.1 cm\({}^{2}\) while treatments determined an increase of leaf area ranging from about 72.0 cm\({}^{2}\) in E1 to 42.1 cm\({}^{2}\) in O1 (Figure 4B; Table A4). Figure 2: Dynamic of the RGR in plant parts of _Tanacetum basamita_. Error bars represent the standard deviation (SD). Different letters above each column indicate significant differences among the treatments ([PERSON]’s test \(p\) < 0.05). Figure 3: Plants and roots grown at different concentrations of Effective Microorganisms and Olive. Mill Wastewater, at time T0 and T3 (final time). Comparing the Control with the treatments the pairwise analysis (Table A3) showed that the maximum value of EF for LN was \(-8.03\) (Control\(\Leftrightarrow\)O1) and the minimum was \(-5.95\) for Control\(\Leftrightarrow\)E2, however, the latter value highlights a strong response to treatment. Among the treatments, the maximum value was observed for E2\(\Leftrightarrow\)O1 (EF = \(-3.54\)) and the minimum was for E1\(\Leftrightarrow\)O2 with EF = \(0.99\) (Table A3). Instead for LA, the comparison between Control and treatment exhibited the maximum value in Control\(\Leftrightarrow\)E1 (EF = \(-4.4\)) and the minimum difference in Control\(\Leftrightarrow\)O1 (EF = \(-0.51\)) (Table A3). In treatment plants, maximum differences were observed in E1\(\Leftrightarrow\)O1 and the minimum in E1\(\Leftrightarrow\)O2, EF = \(3.84\), and EF = \(0.69\) respectively (Table A3). Regarding these results, O1 treatment recorded a leaf area value similar to the Control, but the best result was in leaves number (205). This result is not conflicting, [PERSON] et al. (2014) had already observed an inverse relationship between leaf area and leaf number in _Tanacetum balsamita_ plants treated with different concentrations of N, and they considered this result to be not limiting to plant growth. The estimation of leaf number and leaf area is decisive for plant growth and development being the leaf an essential plant structure that allows gas exchange and the transformation of light energy into chemical energy useful for cellular functions ([PERSON] et al., 2017). The effects of EM and OMW treatments on growth indices SLA (Specific Leaf Area), LAR (Leaf Area Ratio), and LWR (Leaf Weight Ratio), are reported in Table A1 and Figure 4C-E. SLA is a measure of leaf thickness, correlated with the number and/or size of leaf photosynthetic  
Figure 4: Box plots representing the variation in leaf parameters at the end of the experiment, for: **(A)** leaves number, **(B)** leaf area, **(C)** Specific Leaf Area, **(D)** Leaf Weight Ratio and **(E)** Leaf Area Ratio, of _Tanacetum balsamita_ plants in response to the application of EM and OMW biostimulants at two different concentrations. The central line displays the median, the bottom and top of the box are the first and third quartiles. Different letters indicate significant differences (\(p<0.05\)) using the Tukey’s test. mesophyll cells [41]. SLA index showed similar values for E2, O1, and O2 treatments and Control, while E1 treatment reported the highest value (715.2 cm\({}^{2}\) g\({}^{-1}\); Figure 4C).