Spectral Reflectance Properties of Vertisols and Associated Soils of Nagpur District in Maharashtra

Abstract

Morphological, physical, chemical and spectral reflectance properties of soils of Nagpur district, Maharashtra were studied to understand the relationship between soil spectral reflectance and physical and chemical properties of soil. A total of 290 soil samples (both surface and sub-surface and profiles) were collected from 143 sites representing different physiographic units. The soils varied distinctly in Munsell colour hue and the soil texture ranged from sandy loam to clay with smectite as the dominant clay minerals. The soil pH varied from 4.9 to 9.2 and organic carbon (OC) content ranged from 1.0 to 24.4 g kg-1. The soil exchange complex was dominated by calcium (Ca) followed by magnesium (Mg), sodium (Na) and potassium (K). In general, most of the soils were rich in available iron (Fe), manganese (Mn) and copper (Cu) but deficient in zinc (Zn). Reflectance spectra of the soils showed prominent absorption features around 1400, 1900 and 2200 nm wavelength region. The soils with colour hue of 7.5YR, 5YR and 2.5YR showed a broad absorption features around 550 in visible and 950 nm in NIR region due to the presence Fe-oxides. Derivative soil reflectance data were calibrated with different soil attributes using step-wise multiple linear regression technique to develop spectral models for prediction of soil attributes. The developed spectral models showed relatively good prediction of sand (r2 = 0.74; RPD=1.86), clay (r2 = 0.73; RPD=1.85), pH (r2 = 0.72; RPD=1.87), OC (r2 = 0.70; RPD=1.82), exch Ca (r2 = 0.61; RPD=1.48), CEC (r2 = 0.70; RPD=2.16), CaCO3 (r2 = 0.62; RPD=1.54), Fe2O3 (r2 = 0.53; RPD=1.43), DTPA-Fe (r2 = 0.79; RPD=2.11) and DTPA-Cu (r2 = 0.77; RPD=1.96) in the validation datasets indicating that reliable prediction of these properties from soil reflectance data.