## 4 Discussion  
### Media Phytotoxicity and Substrate Properties  
Prior to incorporating biochar into any soilless substrate, simple germination tests could be used to test the phytotoxicity of biochar, and a phytotoxicity assessment is essential for successful soilless amendment [30]. The soilless petri dish bioassay (also known as the germination test) is a rapid and simple preliminary test recommended by [PERSON] to test potential biochar toxicity [35]. In this study, the extracts of SBB, HB, their mixes with PM, PM, P, 70%PM:30%P and the commercial propagation mix all showed no phytotoxicity, which is consistent with [PERSON]'s findings [36]. Biochar may or may not have phytotoxic effects on plants depending on the original feedstock and process conditions [30]. For instance, the biochar from hardwood, corn and switchgrass under different process conditions had no effect on germination rate [29], while biochar from olive mill waste was phytotoxic [37]. In this study, the germination rates of all basil seeds in the aqueous extracts of biochar-amended mixes were higher than those in DI water, which indicated no phytotoxicity for the biochar used in this study. This is similar to what had been found in [PERSON]'s work [29]. However, \begin{table}
\begin{tabular}{l l l l l} \hline \hline
**Mixes \({}^{\text{z}}\)** & **Stalk DW(g)** & **Leaf DW(g)** & **Flower DW (g)** & **Total DW (g)** \\ \hline SBB:PM:P(10:60:30) & \(1.8\pm 0.2^{**}\) & \(4.3\pm 0.4^{**}\) & \(0.4\pm 0.1^{**}\) & \(6.4\pm 0.7^{***}\) \\ SBB:PM:P(30:40:30) & \(3.3\pm 0.2^{**}\) & \(6.2\pm 0.2^{*}\) & \(1.1\pm 0.2^{**}\) & \(10.5\pm 0.5^{***}\) \\ SBB:PM:P(50:20:30) & \(3.1\pm 0.2^{**}\) & \(6.0\pm 0.4^{**}\) & \(0.8\pm 0.2^{**}\) & \(9.9\pm 0.5^{***}\) \\ SBB:PM:P(70:0:30) & \(3.3\pm 0.1^{**}\) & \(5.9\pm 0.2\) & \(1.0\pm 0.1^{**}\) & \(10.2\pm 0.2^{***}\) \\ SBB:PM:P(100:0.0) & \(3.9\pm 0.08^{**}\) & \(6.9\pm 0.3\) & \(1.7\pm 0.3\) & \(12.5\pm 0.3^{*}\) \\ HB:PM(10:90) & \(3.6\pm 0.1^{**}\) & \(6.4\pm 0.1\) & \(1.2\pm 0.2^{*}\) & \(11.3\pm 0.3^{**}\) \\ HB:PM(30:70) & \(4.3\pm 0.1\) & \(7.3\pm 0.3\) & \(2.0\pm 0.2\) & \(13.5\pm 0.4\) \\ HB:PM(50:50) & \(4.4\pm 0.1\) & \(7.3\pm 0.2\) & \(1.9\pm 0.4\) & \(13.6\pm 0.6\) \\ HB:PM(70:30) & \(4.1\pm 0.3\) & \(6.4\pm 0.6\) & \(1.5\pm 0.5\) & \(11.9\pm 0.7^{**}\) \\ Control & \(4.8\pm 0.2\) & \(7.7\pm 0.3\) & \(2.5\pm 0.2\) & \(14.9\pm 0.6\) \\ \hline \hline \end{tabular} Note.: \({}^{*}\)SBB = sugarcane bagasse biochar; HB = mixed hardwood biochar; P = perlite; PM = peat moss; Control = commercial growing substrate. Numbers in parentheses indicate the ratio of different components, by vol.  
\end{table} 
Table 5: Biomass of basil plants transplanted from biochar-amended mixes after four weeks. (*, ** indicate a significant difference from the control using [PERSON]’s test at \(p\leq 0.05\) and \(p\leq 0.01\), respectively). Figure 7: The growth index **(a)** and SPAD **(b)** of basil plants transplanted from biochar-amended mixes after four weeks. SBB = sugarcane bagasse biochar; HB = mixed hardwood bioTA C51 = commercial growing substrate. SBB (10%, 30%, 50%, 70% and 100%; by vol.) incorporated with 30% perlite with the rest being peat moss; HB (10%, 30%, 50% and 70%; by vol.) incorporated with peat moss. (*, ** indicate a significant difference from the control using [PERSON]’s test at \(p\leq 0.05\) and \(p\leq 0.01\), respectively). biochar-amended mixes having no effects on seedling germination rates does not necessarily mean they had no inhibition on shoot growth because plant's shoot growth can be inhibited by polycyclic aromatic hydrocarbons present in aqueous extracts [29], or by the poor physical-chemical properties of the mixes [2]. The seedlings grown in SBB-amended mixes had significantly lower DW than the control, which may be due to their low AS [38]. Even though the effects of biochar on substrate properties also varies depending on original feedstock and process conditions [22; 30], some biochar types have been proven to improve the physical properties of the growing media [39].