5. Conclusion
The study was conducted in the Indo-Gangetic plain region to evaluate the performance of reflectance spectroscopy in the Vis-Nir and MIR regions for estimation of electrical conductivity which is known to affect crop productivity and soil quality. The procedure adopted for testing EC was one that is commonly used in the soil testing laboratories of India and results suggested wide variation of electrical conductivity in the study region. Spectral regions in 460-500 and 1890-1906 nm in the Vis-NIR region and 4200-4310, 5275-5280, 6660-6670, 7305-7310 and 8290-8300 nm in the MIR region were identified as sensitive for estimation of EC. The PLSR model outperformed other models in calibration and validation in the Vis-NIR range and the PLSR model in calibration and RF model in validation was better in the MIR range (followed by PLSR). Among the Vis-NIR and MIR regions, on the basis of higher RPD values, the data fitted better in the Vis-NIR region and would be the region of choice for predicting EC in the study area. Thus reflectance spectroscopy in the Vis-NIR range with PLSR algorithm is very well suited to replace conventional method of estimating electrical conductivity in the intensively cultivated Indo-Gangetic plain regions of India.