FTIR Spectroscopy and Optical Density Characterization of Humic Substances Extracted from Reclaimed Alkali Soils under Different Tillage and Management Practices

Abstract

In the present investigation, different tillage and management practices interventions were assessed to note the changes in the composition of humic substances using Fourier transform infrared (FTIR) techniques, optical density (E4/E6) measurement and elemental composition of humic acid. One uncultivated and four reclaimed alkali surface (0-0.15 m) soil samples after adoption of four years different tillage and management practices were collected from Central Soil Salinity Research Institute, Karnal. Optical density (E4/E6) of fulvic acid was higher than that of humic acid. This was due to the more condensed and more matured nature of humic acid than fulvic acid. The trend of E4/E6 ratio was farmers practices in rice-fallow-wheat cropping system with puddled rice and conventional tillage wheat without crop residue addition (FP in R-F-W) > integrated crop and resource management in rice-wheat-mungbean cropping system (ICRM in R-W-M)> futuristic and diversified (CA) based system of maize-wheat-mungbean cropping system (FDCA in M-W-M) >UnK> Conservation agriculture (CA) based system in rice-wheat-mungbean cropping system (CA in R-W-M). The highest stability was recorded in CA in R-W-M and the lowest in FP in R-F-W. Elemental composition of extracted humic acid revealed that carbon content in humic acid varied from 47.53% in uncultivated soils to 51.32% in ICRM in R-W-M. The nitrogen content in humic acid varied from 4.38% in FDCA in M-W-M to 4.89% in CA in R-W-M. Soils having the lowest C/N value was observed 10.03 in CA in R-W-M and the highest C/N ratio of value 11.72 was recorded in FDCA in M-W-M. Wave no.  (cm-1) & proposed functional group of extracted humic acid revealed that FTIR peak at 1507-1508 cm-1 in CA in R-W-M, aromatic -C=C- peak was absent in FDCA in M-W-M and in FP in R-F-W it was replaced by aliphatic C-H stretch.