Fig. 1. Comparison of before and after atmospheric correction

Fig. 2. Soil reflectance curves at 121 sampling points

Fig. 3. Flowchart of RF-DE-AHP method for extracting soil nutrient characteristic bands

Fig. 4. Schematic diagram of BP inversion model for soil nutrient contents

Fig. 5. Mutual information between soil available potassium and spectral data by RF algorithm

Fig. 6. Spectral band weight distribution of soil available potassium by using differential evolution algorithm

Fig. 7. Weight sorting for soil available potassium by the analytic hierarchy process

Fig. 8. RF-DE-AHP method prediction results. (a) Training set; (b) validation set

Fig. 9. Mathematical transformation method prediction results. (a) Training set; (b) validation set

Fig. 10. RF-DE method prediction results. (a) Training set; (b) validation set

Fig. 11. Evaluation results of the available potassium prediction models. (a) Training set; (b) validation set