| Parameter | Coefficient | Std. Error | Z | P > z |
| SOM | 0.25 | 0.17 | 1.53 | 0.127 |
| pH | −0.89 | 0.45 | −1.98 | 0.047** |
| Na | −0.27 | 0.07 | −3.73 | 0.000** |
| Ws | −1.17 | 0.45 | −2.61 | 0.009** |
| Cl | 0.24 | 0.17 | 1.39 | 0.166 |
| tt | −0.19 | 0.09 | −2.08 | 0.037** |
| Intercept | 8.75 | 1.26 | 6.92 | 0.000** |
| R-sq (overall) = 0.2009 | ||||
| Wald chi square (6) = 43.22 Prob > chi square = 0.0000 | ||||
| Rho = 0.132 | ||||
| Hausman test: chi square (6) = 3.71 Prob > chi square = 0.7165 | ||||