# Popular Biochar as an Alternative Substrate for Curly Endive Cultivated in a Soilless System
## 3 Results
### PCA Analysis  
The findings of the principal component analysis (PCA) displayed four main components (PCs) with eigenvalues higher than 1.00 (Table 6), accounting for 62.58%, 21.59%, 9.19% and 4.14% of the total variance, respectively. \begin{table}
\begin{tabular}{c c c c c} \hline
**Variable** & **PC1** & **PC2** & **PC3** & **PC4** \\ \hline pH & **0.922** & \(-\)0.307 & \(-\)0.201 & 0.077 \\ EC & **0.851** & \(-\)0.444 & \(-\)0.247 & 0.053 \\ N\({}_{\text{substrate}}\) * (N-s) & **-0.957** & \(-\)0.049 & 0.087 & 0.168 \\ P\({}_{\text{substrate}}\) * (P-s) & **-0.981** & 0.130 & 0.026 & 0.087 \\ K\({}_{\text{substrate}}\) * (K-s) & **0.963** & \(-\)0.086 & \(-\)0.225 & \(-\)0.002 \\ C\({}_{\text{substrate}}\) * (Ca-s) & **-0.991** & 0.124 & \(-\)0.001 & 0.027 \\ Mg\({}_{\text{substrate}}\) * (Mg-s) & **-0.954** & 0.027 & 0.055 & 0.237 \\ Na\({}_{\text{substrate}}\) * (Na-s) & **-0.932** & 0.345 & 0.077 & \(-\)0.008 \\ Total porosity (TP) & 0.210 & 0.434 & **-0.863** & 0.038 \\ Particle density (PD) & **0.937** & \(-\)0.243 & \(-\)0.038 & 0.130 \\ Bulk density (BD) & **0.896** & \(-\)0.425 & \(-\)0.099 & 0.047 \\ Head fresh weight (HFW) & 0.592 & **0.745** & 0.013 & 0.303 \\ Head height (HH) & **0.745** & **0.655** & 0.045 & 0.071 \\ Stem diameter (SD) & **0.659** & **0.711** & 0.025 & 0.122 \\ Number of leaves (NL) & **0.790** & 0.571 & 0.002 & 0.207 \\ Head dry matter content (HDMC) & **0.831** & 0.446 & \(-\)0.107 & 0.038 \\ Root dry matter content (RDMC) & **0.692** & **0.703** & 0.075 & 0.080 \\ SSC & 0.352 & 0.366 & **0.846** & 0.115 \\ TA & 0.458 & **-0.678** & 0.245 & 0.490 \\ Ascorbic acid (AA) & **0.763** & 0.404 & 0.488 & \(-\)0.090 \\ Total Phenolic (TPC) & **0.837** & \(-\)0.377 & 0.377 & 0.030 \\ N\({}_{\text{leaves}}\) ** (N-l) & **-0.929** & 0.064 & 0.233 & 0.224 \\ P\({}_{\text{leaves}}\) ** (P-l) & 0.034 & **-0.958** & 0.047 & 0.105 \\ Kleaves ** (K-l) & **0.947** & \(-\)0.242 & \(-\)0.187 & 0.036 \\ Calieves ** (Ca-l) & **-0.726** & 0.584 & \(-\)0.324 & \(-\)0.005 \\ Mgleaves ** (Mg-l) & **-0.604** & \(-\)0.062 & \(-\)0.305 & **0.683** \\ Eigenvalue & 16.270 & 5.613 & 2.389 & 1.077 \\ Variance \% & 62.576 & 21.589 & 9.189 & 4.140 \\ Cumulative \% & 62.576 & 84.165 & 93.354 & 97.494 \\ \hline \end{tabular} Values in bold within the same factor indicate the variable with the largest correlation. * N\({}_{\text{substrate}}\), substrate nitrogen content; P\({}_{\text{substrate}}\), substrate phosphorus content; K\({}_{\text{substrate}}\), substrate potassium content; Ca\({}_{\text{substrate}}\), substrate calcium content; Mg\({}_{\text{substrate}}\), substrate magnesium content; Na\({}_{\text{substrate}}\), substrate sodium content. ** N\({}_{\text{levaves}}\), leaves nitrogen content; P\({}_{\text{levaves}}\), leaves pleasphorus content; K\({}_{\text{levaves}}\), leaves potassium content; Ca\({}_{\text{levaves}}\), leaves calcium content; Mgleaves **(Na-l) & 0.604 & 0.488 & 0.090 \\ \hline \end{tabular}
\end{table} 
Table 6: Loadings scores for principal components PC1, PC2, PC3 and PC4. This evidenced that the twenty-six variables could be articulated as a linear arrangement of four PCs, elucidating 97.50% of the total variance. PC1 was mainly positively correlated to pH, EC, K\({}_{\rm substrate}\), particle density, bulk density, head height, stem diameter, number of leaves, head dry matter content, root dry matter content, ascorbic acid, total phenolic, K\({}_{\rm leaves}\) and mainly negatively correlated to N\({}_{\rm substrate}\), P\({}_{\rm substrate}\), Ca\({}_{\rm substrate}\), Mg\({}_{\rm substrate}\), Na\({}_{\rm substrate}\), N\({}_{\rm leaves}\), Ca\({}_{\rm leaves}\) and Mg\({}_{\rm leaves}\); PC2 was mainly positively related to head fresh weight, head height, stem diameter, root dry matter content, and negatively related to P\({}_{\rm leaves}\); PC3 was mainly positively correlated to SSC, and negatively related to total porosity; and PC4 was mainly positively related to Mg\({}_{\rm leaves}\) (Table 6).