| Variables | Symbols | Levels | |||
| (−) | (0) | (+) | Control | ||
| NaNO3 | X1 | 0 | 0.04 g∙L−1 | 0.08 g∙L−1 | 0.17 g∙L−1 |
| KH2PO4 and Na2HPO4 | X2 | 0 | 0.01 g∙L−1 | 0.02 g∙L−1 | 0.04 g∙L−1 |
| NaCl | X3 | 0 | 5.0 g∙L−1 | 10.0 g∙L−1 | 0 |