## 3 Results and Discussions
### Agronomic Trials by Plant Growth and Lixiviation Tests
\begin{tabular}{l} **Nonlinear Draw** \\ **Oos** \\ **Missing search** \\ **pool (a)** \\ \end{tabular}  &
\begin{tabular}{l} **Connected Attributed** \\  
According to many authors [26; 46; 47], even growing plants with microalgae biomass wasn't better than those grown with synthetic fertilizers or digestate, the use of microalgal biomass for fertilizing purposes presents some important advantages. Microalgal biomass can be considered as a slow-released fertilizer since the application of dried biomass to soils would not result in emissions nitrous oxide and ammonia volatilization, as is the case of digestates [7; 46]. Microalgae biomass presents other advantages over synthetic fertilizers because it is not as pollutant as synthetic fertilizers and microalgae cultivation contributes to the upgrading of the liquid digestate phases without losing fertilizers properties. In parallel, to assess the benefits of using microalgae fertilizers against synthetic fertilizers or liquid digestate as a way to reduce nutrients leaching, the effect of the three fertilization methods (at 170 kg N/ha) was studied using nutrients leaching columns to understand the N (NH4\({}^{+}\), NO2\({}^{-}\) and NO3\({}^{-}\)) leaching once applied the fertilizers in soil. This study was intended to represent a worst-case scenario with extremely heavy rainfall just after adding the different fertilizers. During the 25 days of experiment, similar leachate volumes were recovered from all soil columns (around 18 mL per leaching event). As shown in Figure 5, the soil amended with synthetic fertilizer presented a major loss of N. Interestingly, with microalgae fertilization, only 7% of N was leached, compared to 50% in the case of synthetic fertilizer and 24% for the liquid digestate. The results showed that microalgal biomass retains N better and release it slowly. This slow-releasing nature can be explained because N is in the organic form in microalgal biomass that need to be mineralized to be leached in the mineral form [26]. [PERSON] et al. (2018) also performed leaching nutrients during seven days in columns without plant growth on industrial fertilizers and several digestates on various soils (i.e., loam, sand, slit) [33]. Industrial fertilizers lead to similar nutrients leaching than the present study with 19%-41% of N leached according to the soil origin, with lower leaching observed in silt soil. For all the digestates investigated the nutrient leaching ranged from 17% to 52% which is in agreement with the present results [33]. Nonetheless, such results have to be considered as preliminary assay and should be repeated in pilot lysimeter simulating simultaneous plant growth or just after the harvest period as the N dynamic and loses will not be the same. Furthermore, nutrient leaching potential following application of fertilizers depends on several others factors such as fertilization strategies (e.g., time and methods of application), soil texture (e.g., sand, silt, loam soils), topography, precipitations and cropping systems [9]. Figure 5: Cumulative leached amount of NH4\({}^{+}\)-N, NO3\({}^{-}\)-N, NO2\({}^{-}\)-N (kg N/ha) in soil treated with synthetic fertilizer (SE), liquid digestate (SD) and microalgae biomass (SM). For each condition, the lixiviation due to the control (soil alone) have been subtracted.