Table 2.
Models performance of winter wheat yield based on different variable at different growth stages.
| Variable | Modeling method | Days after lower temperature stress | Calibration set | Validation set | ||||
|---|---|---|---|---|---|---|---|---|
| R2 | RMSEC | RPD | R2 | RMSEP | RPD | |||
| Full spectrum | PCR | 5d | 0.774 | 956.924 | 2.104 | 0.596 | 1938.589 | 1.260 |
| 10d | 0.743 | 1020.769 | 1.972 | 0.306 | 1445.399 | 0.496 | ||
| 20d | 0.777 | 951.373 | 2.116 | 0.718 | 1083.506 | 0.684 | ||
| 25d | 0.879 | 700.921 | 2.872 | 0.854 | 625.700 | 2.364 | ||
| 35d | 0.815 | 866.436 | 2.324 | 0.742 | 833.556 | 1.700 | ||
| 50d | 0.828 | 835.569 | 2.409 | 0.769 | 967.149 | 1.766 | ||
| NDVI | MLR | 5d | 0.619 | 1144.250 | 1.274 | 0.527 | 1904.611 | 0.545 |
| 10d | 0.662 | 1077.768 | 1.399 | 0.539 | 1961.395 | 0.747 | ||
| 20d | 0.734 | 955.582 | 1.661 | 0.670 | 1298.490 | 0.577 | ||
| 25d | 0.791 | 847.378 | 1.945 | 0.731 | 1565.103 | 0.235 | ||
| 35d | 0.691 | 1030.807 | 1.494 | 0.760 | 933.235 | 1.585 | ||
| 50d | 0.577 | 1204.692 | 1.169 | 0.682 | 2884.032 | 1.003 | ||
| Spectral characteristic variable | SPA-MLR | 5d | 0.814 | 1115.045 | 2.199 | 0.549 | 1894.386 | 1.039 |
| 10d | 0.869 | 765.267 | 2.751 | 0.725 | 1003.529 | 1.293 | ||
| 20d | 0.874 | 807.254 | 2.779 | 0.745 | 1047.131 | 0.840 | ||
| 25d | 0.887 | 716.985 | 2.719 | 0.841 | 835.060 | 2.087 | ||
| 35d | 0.787 | 1073.952 | 2.099 | 0.823 | 768.487 | 1.487 | ||
| 50d | 0.714 | 1408.501 | 1.670 | 0.676 | 1041.161 | 1.647 | ||