## 3 Results and Discussions
### Agronomic Trials by Plant Growth and Lixiviation Tests  
The results of Germination Index (GI) (Figure 4a and Table 4) showed that in the trials with soil (without any treatment) GI reached 100% whereas values of 96, 79 and 92% were obtained for pots amended with synthetic fertilizer, digestate and microalgae biomass respectively. However, according to the ANOVA test, no statistically significant differences were obtained. The slight drop in GI for the digestate samples can be explain by some soluble compounds (VFAs, ammonium, trace elements) that might inhibit the germination [3; 44; 45] In general rules, from literature data, no negative effect on germination were observed from digestate at high dilution rate, while high concentrations showed germination inhibition [3; 44]. Then, the impact of the three fertilizers (i.e., synthetic fertilizers, liquid digestate, microalgae added at 170 kg N/ha) is shown in Figure 4a. Plant dried biomass was 24.8 \(\pm\) 0.8, 25.1 \(\pm\) 2.5 and 25.6 \(\pm\) 1.2 g TS/100 plants for respectively synthetic fertilizers, liquid digestate and microalgae showing similar efficiency between microalgae and synthetic fertilizers for same N supply. In other words, microalgae bio-fertilizer enhanced tomato growth by 32% in terms of total plant dried biomass compared to the control (i.e., soil without any fertilizer). Similarly, synthetic fertilizers and liquid digestate lead to 27% and 29% enhancement of the plant dried biomass in comparison to the soil control. Such results demonstrate that microalgae were as effective for growth tomatoes as other fertilizer sources during the first vegetative growth stage (ANOVA \(p\)\(<\) 0.05). Similarly, in the case of leaves number (Figure 4b), 45, 43 and 32% more leaves were found in plants amended with synthetic fertilizer, digestate and microalgae biomass, respectively in comparison with the control tests (soil without fertilization) which it is also an indication of the plant health. Finally, in terms of pigments content (i.e., chlorophyll and carotenoids) (Figure 4c), adding microalgae biomass improved the pigments contents compared to the control trials (without fertilization) but the enhancement was lower compared to the synthetic fertilizer and liquid digestate application. This is probably due to a reduction in the absorption of nutrients needed for chlorophyll production by the plants, especially mineral nitrogen. Contrary to synthetic fertilizers and liquid digestate, nitrogen is available in microalgae in the form of organic nitrogen and should be mineralized before to be used by plants. Likewise, [PERSON] et al. (2005) found that only around 3% of the biomass N was available as mineral N at the time of application and approximately 33% of algal N was converted to plant-available N within 21 days [26]. \begin{table}
\begin{tabular}{c c} \hline
**Parameters** & **Values (\(\pm\) S.D)** \\ \hline
**C (\% TS)** & 30.62 \(\pm\) 0.22 \\ \hline
**H (\% TS)** & 4.04 \(\pm\) 0.03 \\ \hline
**N (\% TS)** & 3.27 \(\pm\) 0.26 \\ \hline
**S (\% TS)** & 0.85 \(\pm\) 0.02 \\ \hline
**K(\% TS)** & 0.55 \(\pm\) 0.02 \\ \hline
**P(\% TS)** & 0.90 \(\pm\) 0.2 \\ \hline
**Ca (\% TS)** & 0.45 \(\pm\) 0.02 \\ \hline
**Mg(\% TS)** & 0.25 \(\pm\) 0.08 \\ \hline \end{tabular}
\end{table} 
Table 3: Main chemical properties of the microalgae cultivated and harvested in this study. The elemental composition of the tomato plants grown in different conditions is given in Table 4. Similar C content were found for all the conditions. The most noticeable results were observed for nitrogen in the plants cultivated in soil alone (control) and microalgae fertilizers, where N content was lower than those found in the composition of tomato plants cultivated in the synthetic fertilizers and liquid digestate. The benefits of using liquid digestate or microalgae to enhance growth plant tests have been previously demonstrated to be as efficient as synthetic fertilizers [26; 30].