Spectral Reflectance Characteristics of Na-carbonate Irrigated Arid Secondary Sodic Soils

Abstract

In the arid region of Rajasthan, India, saline ground water containing elevated residual Na-carbonate (RSC) is frequently used for raising winter crops. Relationships between spectral reflectance characteristics of RSC water irrigated sodic soils under differential management with their physicochemical and crust characteristics have been investigated. Studies have been carried out at four sites irrigated with saline/high RSC water (EC 4.0 to 10.1 dS m -1 , Na adsorption ratio (SAR) 21.8-45, adjusted SAR 45.8-98.1 and RSC nil to 19 mmol c L -1 ) for more than 10 years. Some of the parcels have received gypsum for amelioration and have received differential management. The spectral values were higher at Site 2 (32.3-42.1%) followed by Site 1 (18.2-23.2%), and Site 3 and Site 4 (11.1-20.5%). Higher reflectance values were obtained at 800 nm and 1,000 nm wavelengths, followed by 460 nm, and the lowest at 620 nm. At Site 1 and Site 2 low penetration values (0.05-4.24 kg cm -2 ) were associated with higher soil water content. At Site 3 and Site 4 large penetration resistance (29.06-46 kg cm -2 ) was attributed to low water content. The multiple regression analysis involving eight soil parameters could predict spectral reflectance to the extent of 99.7% of total variance. The spectral reflectance shows a negative relationship with soil water status, and positive relationships with soil salinity and pH value. For the remote sensing of soil salinity and sodicity in the area, the fallow season of May and June is suggested.