# Malaysian Virgin Soil Extracts as Natural Growth Enhancer for Targeted Green Microalgae Species
## 3 Results and Discussion
### Effects of Soil Extracts on the Growth of Microalgae
The addition of soil extracts was indeed instrumental in increasing the biomass of microalgae as evidenced by the findings reported by [PERSON] [37]. The supplementation of 7% soil extracts assisted the production of higher biomass with the specific growth rate of 0.82 d\({}^{-1}\) of _Nannochloropsis_ sp. after 16 d of the incubation period. Likewise, the production of _Cosmarium subtumidium_ increased in terms of growth rate, cell number (biomass of 2629 cells per mL), and doubling time when the cultivation medium was augmented with soil extracts [38]. Accordingly, the rise in the concentration of soil extracts has affected the growth in the number of cells. Although the soil extracts obtained from the autoclave treatment method at 121 \({}^{\circ}\)C twice yielded the highest nutrient recovery, the soil extracts resulting from this method of treatment did not support the highest specific growth rate of any of the microalgae species which may be due to some species dependence and variability [19]. In addition, the presence of higher microalgae populations may limit nutrient availability and this hinders \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Modified Soil Extract**} & \multicolumn{3}{c}{**Specific Growth Rate (SGR), \(\mu\) (d\({}^{-1}\))**} \\ \cline{2-4}  & _Nannochloropsis_ & _Nannochloropsis_ & _Chlorella_ \\  & _ocenica_ & _oculata_ & _sorokiniana_ \\ \hline Control medium & 0.032 \({}^{\circ}\)\(\pm\) 0.001 & 0.020 \({}^{\circ}\)\(\pm\) 0.001 & 0.038 \({}^{\circ}\)\(\pm\) 0.001 \\ Medium + 105 \({}^{\circ}\)C once & 0.038 \({}^{\circ}\)\(\pm\) 0.005 & 0.071 \({}^{\circ}\)\(\pm\) 0.001 & 0.067 \({}^{\circ}\)\(\pm\) 0.002 \\ Medium + 105 \({}^{\circ}\)C twice & 0.059 \({}^{\circ}\)\(\pm\) 0.003 & 0.105 \({}^{\circ}\)\(\pm\) 0.001 & 0.073 \({}^{\circ}\)\(\pm\) 0.002 \\ Medium + 121 \({}^{\circ}\)C once & 0.069 \({}^{\circ}\)\(\pm\) 0.003 & 0.069 \({}^{\circ}\)\(\pm\) 0.003 & 0.080 \({}^{\circ}\)\(\pm\) 0.001 \\ Medium + 121 \({}^{\circ}\)C twice & 0.032 \({}^{\circ}\)\(\pm\) 0.005 & 0.087 \({}^{\circ}\)\(\pm\) 0.007 & 0.076 \({}^{\circ}\)\(\pm\) 0.004 \\ Medium + 24 h & 0.037 \({}^{\circ}\)\(\pm\) 0.003 & 0.114 \({}^{\circ}\)\(\pm\) 0.007 & 0.048 \({}^{\circ}\)\(\pm\) 0.005 \\ \hline \hline \end{tabular} Note: The values displayed are the average for replicates of three with standard deviation. *\({}^{\circ}\) The overall mean of the same column with distinct superscripts changes significantly (\(p\) < 0.05) using ANOVA and Tukey post-hoc.  
\end{table} 
Table 4: Specific growth rate, \(\mu\) of _Nannochloropsis ocenica_, _Nannochloropsis oculata_, and _Chlorella sorokiniana_ in different modified soil extract medium. the increase in total biomass concentrations over time [36]. The 96-well plate culturing method employed in the present study may contribute to certain growth inadequacies due to low volume (microwells) and eventual high concentration of the microalgae biomass on day 9 [31]. The division rate (_k_) displayed the same trend as the specific growth rate (\(\mu\), d\({}^{-1}\)), whereby a significant difference was seen when a different modified soil extract medium was used (_p_ < 0.05) as shown in Table 5. The greatest division rate of _Nannochloropsis oculata_ was achieved with a modified soil extract medium (24 h natural extraction) amounting to 0.165 \({}^{\text{a}}\)\(\pm\) 0.007. Modified soil extract medium from the autoclave treatment method at 121 \({}^{\circ}\)C once on the other hand contributed to the highest division rate of 0.099 \({}^{\text{a}}\)\(\pm\) 0.003 and 0.116 \({}^{\text{a}}\)\(\pm\) 0.001 for _Nannochloropsis ocanica_ and _Chlorella sorokiniana_, respectively.